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In the development of "psychology," the study of the mental life and activities of animals and men, three phases can be conveniently distinguishedthe presystematic, the systematic but prescientific, and the scientific. The presystematic, by far the longest of the three phases, is that in which men observed and reflected on human ways and embodied their reflections in aphorisms, anecdotes, and fables. Presystematic thinking is important since it has been passed down through the ages and is continually augmented by that amalgam of wisdom, superstition, and dogma that those who claim no professional competence like to describe as the fruits of their experience. The presystematic psychology of contemporary primitive groups has been recorded by anthropologists, but little is known of the corresponding ideas of the precursors of the systematic psychology of the European tradition. The doctrines of the pre-Socratic philosophers are transitional.

Systematic Philosophy of Mind

mind, body, and nature

Systematic psychology began with Aristotle's De Anima, which was of outstanding importance at an early stage because it provided a solid, biologically based conceptual scheme. This involved, first, an elucidation of the concept of soul (ψύχη ) and such related concepts as mind (νου̑ς ), which were regarded as the differentiating properties of the phenomena to be studied. Aristotle's scheme laid down the lines along which the relationship between various manifestations of soul and mind were conceived until the seventeenth century.

Second, life and mind, being closely connected with the functioning of the body, must be conceived of in a way that does justice to the peculiar intimacy of this relationship. Aristotle paid close attention to this relationship.

Third, there is the problem of how the relationship between psychological phenomena and other phenomena of the natural world is to be conceived. Are psychological concepts and categories of explanation reducible to others? Aristotle, again, was particularly interested in this question because of the attempts of some of his contemporaries and predecessors to show that human behavior fell under the concept of motion, which had a wide applicability in the natural world.

In the exposition of the systematic period of psychology these problems will be employed not simply as a framework for expounding the main lines of Aristotle's system of psychology but also as a framework for picking out the main features of the most important theoretical systems since Aristotle laid the foundation of psychology.

plato and aristotle

Aristotle (384322 BCE) insisted on the widest possible definition of soul, thus returning to the pre-Platonic view that soul is virtually the principal of all life. The natural expression for a living thing was μψυχον σω̑μα "body with a soul." Aristotle started from the linguistic point that some bodies are so described whereas others are not and asked by what criterion this distinction was made. His answer was that it is life but that there are different levels of life. Intellect, sensation, nutrition, motion, are all forms of being alive. What they have in common, however, is a self-originating tendency to persist toward an end.

This marked both a return to and a great improvement on pre-Platonic views of soul. In early Greek thought soul was thought of simply as that which keeps a man alive and which leaves his body when he dies. It was connected with breathing. Spirit (θύμος ), on the other hand, was thought of as the generator of movement; it was connected with the movement of the limbs and with emotional states. It was thought of as quite distinct both from soul and from mind, which was regarded as the source of images and ideas. The notion of the soul as a whole of which spirit and mind were attributes emerged only gradually.

Plato (427?347) tried to combine the concept of the soul as a whole with a stress on the preeminence of mind, which he inherited from Anaxagoras. His account, therefore, of the soul as a whole was constantly confused by the special status that he accorded to mind. In the Republic he spoke of the soul as having three partsreason or mind, spirit, and desire (πιθνμία ). But he also thought that reason was the defining property of an immaterial substance that survived bodily death whereas spirit and desire passed away with the body. Similarly, in the cognitive sphere he regarded sensation and imagination as inferior to reason and as intimately connected with the body. This represented a fusion of the Orphic belief in the survival of the soul with an exaltation of mathematical reasoning as the only way of obtaining certain knowledge, which Plato took from the Pythagoreans. He thought that in mathematics the soul grasps forms that are eternal and nondeceptive. As like can be known only by like, the soul, in its rational aspect, must also be eternal. Plato's conviction was reinforced by such considerations as those that he adduced in the Meno, in which the grasp of mathematical truths was exhibited in an untutored slave. According to Plato, this indicated that the slave was being made to remember what he had known previous to his embodiment. Thus, Plato's preoccupation with epistemology led him to make a sharp cleavage between the rational and irrational parts of the soul.

Aristotle approached the matter from a biological rather than an epistemological standpoint. Reason, spirit, and desire represented different levels of being alive. To be alive is to possess a self-originating tendency toward an end. This is exhibited at the lowest level in nutrition and reproduction. Thus, plants have a low-grade soul. Animals have sensation, locomotion, and desire superimposed upon nutrition and reproduction. Human beings, in addition, have reason, or mind, by means of which a rule or plan is imposed upon desire. By mind is meant self-direction in accordance with a rational formula.

Aristotle maintained that the lower level of soul is a necessary condition for the higher and that the possession of a higher type of soul also changes the way in which the lower functions. Because humans are rational, they feed, reproduce, perceive, and act in a manner that differs from that of animals.

Soul and body

Plato's view of the special status of reason was plausible at a time when almost nothing was known about the functioning of the brain and nervous system, for abstract thought seems to proceed with little dependence on bodily organs. Furthermore, the identity of a subject of experience through time does not seem to depend entirely on bodily continuity. There is thus a case for Plato's concept of the rational soul as some kind of active agency that inhabits the body for a brief period.

Plato thought that the rational soul inhabits the head because the head is round (the most perfect shape and, hence, an appropriate place for the seat of reason) and the part of the body nearest the heavens. It makes contact with the brain, which was conceived of as a kind of marrow encased in the skull. The irrational soul makes contact with the marrow of the spinal cord in its bony sheath. The better part of the irrational soul, spirit, inhabits the heart and functions in such manifestations of life as energy, courage, and ambition; the worse part, desire, functions below the diaphragm, in appetite, nutrition, and reproduction. The rational and irrational parts affect each other through the liver, which acts as a sort of mirror of thought.

In sleep the soul is shut up, and its motions subside. A few agitations remain, however, and produce dreams. Usually dreams are the expressions of desires that are suppressedan interesting anticipation of Sigmund Freud's theory of dreams. The good man controls his desires sensibly and so is not unduly disturbed by them in sleep. In the Republic Plato also suggested that in sleep the rational soul, if not troubled by irrational desires, can attain truths not otherwise revealed.

Plato thought of sensation as a transmission of motions. The human body receives an impression from without and responds with an inner motion. Some parts of the bodyfor instance, the hair and the nailsare subject to shock but do not respond with inner movements. Sense organs, however, are good conductors of motion. Thus, hearing, for instance, is the end product of a kind of shock. By means of air in the cavities of the body a blow is transmitted through the ears to the blood and brain and then to the soul. Knowledge does not consist just in sensation but in the activity of the soul in relation to what is thus transmitted. This transmission is complicated by the intervention of memory, imagination, feeling, and association, all of which act as intermediaries between reason and sensation.

Aristotle believed that there was a very intimate connection between soul and body that was a particular case of the more general relationship between form and matter. The soul is "the first actuality of a natural body furnished with organs." He used other examples to illustrate this relationship. If the eye were an animal, he said, eyesight would be its soul, this being the form or capacity of the eye. To speak of soul is to speak of a capacity or propensity to function in a certain way that depends on a certain bodily structure, or it is to speak of the actual exercise of such a capacity or propensity, which is the second kind of actuality. Thus, anger, for instance, can be the appetite of returning pain for pain or the boiling of the blood around the heart, depending on whether the dialectician or the physical scientist is considering it; there is always a biological and a psychological account to be given.

The soul, Aristotle argued, is the cause of the body in three ways. It is its efficient cause in that reference to some concept, such as desire, is required to explain movement. It is the formal cause in that behavior is explained as the exercise of a capacity or tendency. It is the final cause in that reference must be made to "the reason for the sake of which" movements of the body take place. If the behavior is explained by recourse to the rational soul, then plans and rules are imposed on desire. In choice, for instance, means are worked out and adapted to attain an end.

Generally speaking, Aristotle held that soul and body are a particular case of the more general correlatives, form and matter. When he spoke of theoretical reason rather than practical reason, he suggested that the distinction between matter and form is again exemplified in that reason is both passive and active. But he hinted at another sort of doctrine when he also claimed that active reason comes from without and is divine. It is like a helmsman in a ship. This looks like a concession to the Platonic view of mind.

The details of Aristotle's physiology were carefully related to his idea of the levels of soul. The primary function of the nutritive soul is the absorption of nourishment, but its end is to generate another being like itself. The unity of the species is thus preserved though individual members perish. The stomach was thought of as an oven where animal heat cooks the food and blood in the heart. The heart is the seat of life, sensation, motion, and heat.

Sensation is a discriminative power from which the higher cognitive functions develop. There is the organ, the power to receive sensible forms, and the sense, regarded as constituted of both matter and form. In sensation the sense organ is assimilated to its objectfor example, the eye becomes colored. But whereas in nutrition both matter and form of external objects are absorbed, in sensation only form without matter is taken in, like wax taking the imprint of a seal ring. Each sense is sensitive to one or more qualities ranging between extremes. Too little would not register; too much would destroy the organ. This was an application of Aristotle's doctrine of the mean that he developed in relation to moral conduct.

The particular senses are all developments of touch, depending on the intervention of a more refined medium. Taste, for instance, apprehends the savory properties of bodies through the intermediary of moisture; smell, the odorous properties conveyed through the air. In the transmission of sensations to the heart and in the vitality that flows from the heart, the "connatural spirits" play an important role. They were thought of as a kind of inner air quite distinct from the outer air that we breathe. Closely associated with the blood, they acted as a universal internal medium for the transmission of sensation. Besides the specific senses there is sensus communis, which is not a sixth sense but a generic power of sensation as such which provides unity for the sensitive soul in its particular manifestations. The ear does not see; however, the man who hears also sees, and some qualities are presented through more than one sensefor example, roundness by sight and touch. By sensus communis we also perceive the common sensibles of figure, motion, rest, magnitude, and also what Aristotle called the accidental sensibles, which are the principles of association of ideassimilarity, contiguity, and the like. We also perceive that we perceive through sensus communis.

Imagination is a by-product of sensation. Forms provided by sensation are manipulated in the absence of physical objects. Memory is a combination of imagination and sensus communis. There is an image of something plus an awareness of its pastness. Recollection is rather different, for it involves the exciting of an image and the release of a whole chain of images joined by habit according to the principles of association. Imagination also provides a link between knowledge and action, for desire presupposes the imagination of an end to be attained. It may be deliberative, if influenced by reason, or merely sensitive. Desire is thus dependent on sensation and thought. In this way Aristotle was able to maintain his three levels of soul by making desire appear at two levels, depending on whether it is rational or irrational.

Psychological and mechanical concepts

Aristotle believed not only that there were certain very general concepts, such as form, matter, and change, which could be applied to everything; he also extended teleological categories of explanationhis ill-fated final causesto all nature. Nature, he thought, was composed of natural kinds that could be classified by genus and differentia, which all had a natural place, and which all tended toward the realization of their essence. "Nature, like mind, always does whatever it does for the sake of something, which something is its end." Such modes of explanation proved singularly unfruitful when extended to the physical world. But because they were taken from the realm of life, where Aristotle, a marine biologist and the son of a doctor, was particularly acute, they fitted very well, in a general sort of way, that realm of phenomena in which they had their natural home. Aristotle was often accused by later mechanists of being anthropomorphic, but there is not much wrong with being anthropomorphic about men. Indeed, those who later attempted to explain human behavior in mechanical terms applicable to the physical world may well have made the obverse mistake to Aristotle's.

Aristotle himself, in criticizing the mechanists of his day, gave some very interesting arguments to show why the soul, which is the source of movement, cannot itself be moved. Plato had steadfastly claimed that the soul was the source of motion. In a famous passage in the Phaedo (98b99d) he made clear his objection to extending mechanical explanations to cover human conduct. Plato admitted that some kind of physical account could be given of the movements that led up to Socrates' sitting in his prison cell, awaiting his death. But he scorned the suggestion that this account would be a satisfactory explanation of the situation, for an explanation must include some reference to Socrates' reasons for being there. Plato did not, however, develop elaborate arguments against mechanical theories.

Aristotle, on the other hand, wrote his De Anima as part of his systematic attempt to classify the different sciences on the basis of the subject matter with which they were concerned. He was therefore very much concerned both with demarcating the field of application of various families of concepts and with sketching the ways in which they were related to each other. Movement (κίνησις ) was only a particular type of change. He was most anxious to deny that it was either the only or the fundamental type.

Aristotle argued, first, that a logical mistake is made if the soul as a formal cause is thought of as moved in the physical sense. How can a capacity or tendency be conceived of as moving or being moved? Nor can the actualizations of soul in particular cases be properly conceived of as movements, for in practical thought the processes have unity because they go on for the sake of some end. Their particular type of unity cannot be assimilated to such physical unities as the parts of a spatial magnitude; it is more like the unity of a series of numbers. Reference to an end is a conceptual device for picking out how a series of movements are to be thought of as constituting one action; such an end is not itself an extra movement. In the case, too, of some processes of theoretical thought, such as inferring, "thinking has more resemblance to a coming to rest or arrest than to a movement." The end is, as it were, built into the meaning of the term. "Inferring," "concluding," and even "perceiving" are terms that intimate the attainment of ends or standards that are intrinsic to the processes themselves.

Concept of consciousness

Arguments of the Aristotelian type have been revived in recent times by such philosophers as Gilbert Ryle, who have defended a predominantly Aristotelian concept of mind in opposition to a Platonic or mechanical concept. Such a concept of mind is in keeping with the biological orientation of psychology that followed the impact of Charles Darwin. However, it sprang out of the post-Wittgenstein reaction against privacy as the hallmark of the mental, which had characterized most psychological theories since the time of René Descartes (15961650).

It is difficult for modern Western scholars to grasp that the Greeks really had no concept of consciousness in that they did not class together phenomena as varied as problem solving, remembering, imagining, perceiving, feeling pain, dreaming, and acting on the grounds that all these are manifestations of being aware or being conscious. Historically, this emphasis on private experience presupposed the development of individualism as a social movement. The Greeks of the city-states lived in a public world of public feats and public concerns. Their word δίωτης, from which we derive the word idiot, was a term of disdain for a man who concerned himself only with private matters. Socrates, with his stress on individual self-knowledge and the care of the individual soul, was a moral innovator. With the conquests of Philip and Alexander the Great and the breakup of the small autonomous Greek states, this moral innovation became systematized in the codes of the Stoics and Epicureans. The ideal of individual self-sufficiency developed as a substitute for the much-lauded self-sufficiency of the city-states. Man, it was claimed, was a citizen of the world who should either discipline himself and purify his individual soul (Stoics) or slip through life unobtrusively by cutting down the possible sources of misery (Epicureans). This led to an increase of interest in the will and the emotions and to an emphasis on individual experience.

This turning inward was institutionalized by Christianity, with its stress on personal salvation and the purity of soul. Introspection vied with revelation as a source of knowledge. St. Augustine paved the way for Descartes's first certainty, cogito ergo sum. With Descartes the Platonic view of the soul and of knowledge was reinterpreted in the light of the rise of the mathematical sciences, but there was a differencethe stress on the certainty of our knowledge of our own mental states. Mind was no longer simply associated with reason; it was something to which we have private access and whose rational activity it is self-contradictory to doubt. This stress on privacy as a hallmark of the mental was a far cry from Aristotle's view of soul as characterized by a self-originating tendency to pursue an end. A brief mention, however, should be made of some of the intervening systems, though from the point of view of psychological theory, nothing of any great importance happened after the death of Aristotle in 322 BCE until the seventeenth century, when new systems were inspired by the rise of the physical sciences.

stoics and epicureans

The Stoics and Epicureans provided an interesting contrast in respect to their views about the relation between soul and the rest of nature. Both attempted a monistic view, but whereas the Stoics reverted to Plato and tried to extend the concept of soul so that it permeated all nature, the Epicureans reverted to Democritus and extended a mechanical atomistic account of nature to include life and mind.


The Stoics thought of everything in the universe as being either active or passive; hence, there was no opposition between dead matter and soul. The ultimate substance is fire, which has different forms at different levels of being, ranging from cohesion at the inorganic level, through growth at the plant level, to life of a rational or irrational type at the animal and human level. Fire is thus the all-pervading principle of activity as well as the reason or regulator of change in the universe. Mental activity as found in men is a concentrated form of the universal reason, creatures being vehicles for the operation of this universal regulation. Hence the Stoic injunction to live according to nature, for in simple instinctive tendencies reason is often manifest in an incorrupted form.

The Stoics believed that the soul of man is a very subtle form of the all-pervasive fire, for the corporeal can be affected only by what is corporeal. The soul is affected by the body; therefore, the soul, too, must be corporeal. It combines heat, mobility, and a high degree of rarefaction. Indeed, it was more or less identified with the "connatural spirits" of Aristotle that course through the body closely associated with the blood, which are transmitted in generation, and which are similar in nature to the warm outer air, which is also essential to life. The breast is the seat of the soul.

Perhaps the most interesting and important contribution of the Stoics to psychology was their application of the Aristotelian categories of activity and passivity, which they thought to be the defining attributes of what is real, to the mind. Mental activity, they held, is characterized by assent (σνγκατάθεσις ), which can be exhibited in perception and memory, as well as in practical and intellectual judgment. This may be justified or erroneous, but truth is natural and error unnatural. When error of a perceptual, intellectual, or practical kind occurs, the explanation is to be sought in the theory of emotions or mental disturbances. Basic to this Stoic account was the notion of impulse, which covered both appetite and aversion and which operates obscurely at the level of sensation as well as at the rational level, when it is transformed into the adoption of ends for action. Emotions are thus unsuccessful attempts at full rational choice. The early Stoics left such failures unexplained; the later Stoics assigned the cause to circumstances and, therefore, to things that are beyond our power. From this came their characteristic emphasis on the assertion of will over adversity, of rational choice over irrational promptings.


The main interest of Epicurean psychology was its anticipation of mechanical theories of the seventeenth and subsequent centuries. Everything, Epicurus (341270 BCE) believed, was constructed from atoms and, therefore, everything, including minds, could be explained in terms of the mechanical laws governing atoms. The soul differs from other atoms in that it is lighter and more mobile; heat is fundamental to its nature, but it is not identical with fire. It permeates the body like a subtle air and gives it life.

Sensations are effects produced in sense organs by effluxes from objects, differences in sensations being explained in terms of differences in external movements and in the configurations of the underlying atoms. Similarly, ideas are caused by atoms striking the subtle matter of the thinking soul. Incoming impressions set up other motions in the mind, making possible judgment, which is a motion of the mind superimposed upon an impression. Error occurs when impressions are accompanied by irrelevant motions of the mind. The motions of the mind can be linked together to form complex ideas by principles of association. Reason is simply the use of general ideas brought about by the fusion of images into composite pictures.

It is difficult to see how notions such as error and truth could be generated by such descriptions of mere movements of atoms. Indeed, Epicurus did nothing to meet Aristotle's acute criticisms of mechanical descriptions of thought. He did something, however, to meet the charge of fatalism in his notorious doctrine of the swerve of the atom, which was a consequence of the self-motion postulated for all atoms. The power of the mind to incline this way or that constitutes its freedom. People are poised between pain, which is one sort of motion, and pleasure, which is an excessive reaction to pain. Between these two extremes there is an equilibrium, which is more permanently satisfying and which reason can guide men to attain. This he called freedom from disturbance (ταράξια ), which is inseparable from the use of reason.

theological psychology

The psychology of the Greeks had always been, in varying degrees, subservient to epistemological and ethical concerns. The account of reason, for instance, or the role ascribed to the passions was a graphic way of presenting solutions to problems about knowledge and conduct. But there was also the Greek passion for speculation about the ultimate nature of things, about the One in the many, and about the status of mind in the universe and its relation to the body. With the coming of Christianity, which brought with it the biblical account of the creation of the world, this radical metaphysical speculation abated, and the body was seen largely as something that had to be considered as a potent source of temptation. Psychological theory became almost entirely an offshoot of epistemology and ethics, for the supreme purpose of life for thinking men became the knowledge of God and the quest for salvation.

The religious preoccupations of such writers as Plotinus, Clement, and Augustine introduced, of course, a different emphasis into epistemology and ethics. This was manifest before the coming of Christianity in the work of Philo Judaeus (fl. 20 BCE40 CE), who thought that real knowledge was a possession only of minds that had been so purified that they received divine illumination. Philo was the first systematic thinker to fuse the religious fervor of the Hebrew tradition with a selection from the conceptual schemes of Plato, Aristotle, and the Stoics. Knowledge of God and a divinely sanctioned code of conduct had somehow to be fitted into the speculative schemes of the Greeks. Because neither God nor his purposes are manifest to the senses, increasing importance was attached to inner experience as a way of knowing. Philo even wrote a treatise titled On Dreams Sent from God.

This shift of emphasis from the outer world to the inner world is clearly seen in the Neoplatonism of Plotinus (c. 204270). Plato, like all the Greeks, was supremely interested in action, politics, and the external world. His theory of Forms was, in the main, explanatoryhis version of the search of the Greek cosmologists for the One in the many. Even the supreme Form, the Form of the Good, was both the source of the intelligibility of the world and the supreme ideal of action. Plotinus, on the other hand, saw mystical contemplation and absorption in the One as an end in itself. Psychology therefore became harnessed to the exploration and mapping of inner experience. As G. S. Brett remarks in his History of Psychology : "In Plotinus, for the first time in its history, psychology becomes the science of the phenomena of consciousness, conceived as self-consciousness" (R. S. Peters, ed., rev. ed., p. 206).

With the adoption of Christianity as the official religion of the Roman Empire a place had to be found for revelation as well as for knowledge found in inner experience. Augustine (354430) managed to combine these two sources of knowledge. Insofar as there was no revealed doctrine on a matter, he dealt with it within the framework of Platonism penetrated by Christian mysticism. For instance, the growing knowledge of the self and of God was fitted into a Christianized version of Plato's doctrine of reminiscence. Questions about the body, on the other hand, were dealt with by an appeal to the Scriptures. So, too, was the origin of the soul, for it was transmitted into the body when God breathed upon Adam. The lasting influence, however, of Augustine's Confessions was the importance attached to introspection and private experience. No man can escape from his own experience; he can obtain knowledge, insofar as he does not rely on revelation, only by working backward to the presuppositions of his experience as a thinking being. In this approach to the mind Augustine anticipated Descartes.

A corrective to this extreme subjectivity was provided by the rediscovery of Aristotle and the meticulous transmission of his texts by Islamic theologians. The adaptation of Aristotle in the service of Christian theology reached its climax in the work of St. Thomas Aquinas (1224?1274). But using Aristotle as a substructure to support Christian theology was not entirely straightforward. To start with, there was the problem about the status of reason, one of the most debated topics during the Middle Ages. Aristotle's account of the Active Intellect suffered from notorious obscurities, and there was the worry about its relation to revelation as well. Furthermore, the Islamic school, culminating in Averroes, had tended to favor a mildly pantheistic interpretation of Aristotle's doctrine of Active Intellect. Averroes held that the reasons of individuals are but fleeting manifestations of universal reason. Thomas rejected this interpretation, completely following his teacher Albert the Great (c. 1193/12061280).

Thomas defined intellect as the faculty of comprehension that each individual possesses as an intelligent being. Nevertheless, reason was still regarded, as by Plato and Aristotle, as the mark of man's difference from animals and as, in some sense, superhuman. It is qualitatively distinct from sensation and any other processes that are intimately connected with the body.

Apart from this query about the status of reason, which was itself a legacy from Aristotle, Thomas tried to stick to the Aristotelian view of the soul as the form of the body. He deliberately rejected the more Platonic theory that a man is a soul using a body. It was not just respect for the authority of Aristotle that influenced Thomas. The fact was that Christianity was committed to the belief in the resurrection of the body. The intimacy of the connection between soul and body postulated by Aristotle was a better foundation for this doctrine than the more Platonic view occasioning that contempt for the body that culminated in the Albigensian heresy that the body had been created by the devil. Thomas followed Aristotle closely in his account of sensation, sensus communis, memory, and imagination. What was lacking was Aristotle's stress on striving toward an end as the defining characteristic of soul. The intuitive certainties of self-consciousness explored by Augustine remained the foundation both of psychology and of epistemology.

Scholasticism has now become a byword for sustained attention to minor questions within a system whose foundations in revelation were not questioned. There is point in such criticisms. Nevertheless, the Schoolmen preserved and spread a tradition of disciplined discussion that is the lifeblood of science and philosophy. Furthermore, in psychology they handed down not only the general outlines of Aristotle's conceptual scheme but also the details of his psychological system.

The great natural philosophers were nurtured in this Aristotelian tradition even though they eventually overthrew it. At Padua, for instance, where Galileo Galilei was trained, there was a flourishing branch of the Averroistic type of Aristotelianism. Descartes was trained by the Schoolmen at La Flèche, and his Passions of the Soul bears witness to these early influences. Even Thomas Hobbes, one of the archenemies of Aristotelian essences, relied on Aristotle's Rhetoric for the details of his psychology. He merely poured a traditional content into a mechanical mold that he adapted from Galileo, Pierre Gassendi, and the ancient atomists. The Schoolmen provided the thinkers of the seventeenth century with something solid and disciplined to revolt against. And, as with most rebels, these thinkers were really revolting against a mass of assumptions that were deeply embedded in their own consciousness. Indeed, in a certain sense their revolt was only a return to other elements in their intellectual heritagethe precipitates left by the Pythagoreans, Plato, and the atomists.


Descartes's view of the mind was a return to Plato, enriched by the introspective musings of Augustine and made more precise by developments in the natural sciences.

Nature and mind

The natural sciences had made leaps forward not because of a vast accumulation of new facts, though one of the features of the Renaissance had been man's turning his gaze out toward the natural world; it was, rather, because of the amazing success that had attended the application of geometry to the phenomena of the natural world.

The success of geometric thinking about nature tended to corroborate what Plato had said about the status of reason as contrasted with the senses; it also convinced the new natural philosophers like Johannes Kepler, Galileo, and Descartes that the real qualities of the natural world were those which could be treated geometrically. Matter was homogeneous, as the atomists had said. Qualitative distinctions, which had been exalted by Aristotle into irreducible natural kinds, were appearances of the varying motions and configurations of the underlying bodies. The Aristotelian doctrine of form and matter was banished; so were the final causes that he had postulated in nature.

How, then, was mind to be conceived, once the Aristotelian doctrine of form and matter had been discredited? There were two obvious possibilities. One was to adopt Epicurus's view that soul and mind were configurations of light and mobile atoms. The other was to revert to the Platonic view that mind is an altogether different type of substance that inhabits the body. Descartes adopted the second course, partly because he shared Plato's view about the wonder of reason and its difference from sensation and bodily processes and partly, no doubt, because of his Christian convictions about God, freedom, and immortality.


Descartes's departure from Aristotle was much more radical in his account of the soul than in his account of the mind. Whereas Aristotle had described the soul, even in its most primitive manifestations, in teleological terms, Descartes attempted to describe all its lower functions, which were connected with the body, mechanically. His account of mind was not dissimilar in its main outlines from Aristotle's account of reason, which was the most Platonic part of his doctrine, for both accounts held that mind comes from without, furnishes the ultimate principles of thought, and may be considered apart from the body. Indeed, Descartes stated emphatically that the mind can think without a body.

For his account of mind Descartes looked into himself in the manner of Augustine, but he rejected that reliance on faith which was epitomized by the protestation Credo quia absurdum ("I believe because it is absurd"). Nothing that was not clearly and distinctly present to the mind was to be included in a judgment. Everything must be doubtedeven mathematical truthsuntil a belief can be found that applies to what exists and that it would be self-contradictory to deny. Descartes's cogito ergo sum his more precise rendering of Augustine's intuitive certainty about his existence as a thinking beingwas the result.

Descartes explored the rest of what was intimated in this first certainty and tried to spin out of it all sorts of other truthsfor example, the existence of God and of an external world. The details of his attempted demonstration do not concern us here. They effectively established, in Descartes's view, the existence of thinking substances that were innately so constituted that they would come to form clear and distinct ideas of extension, figure, motion, and other simple natures. Ideas are all mental; as images they are presented through bodily processes, images being apparently corporeal.

Minds were thought to be passive in cognition. When a mind is thinking clearly and distinctly, its ideas correspond to the real qualities of objects. But minds are also active in volition. At the intellectual level their activity consists only in assent to the necessary connection between ideas, and volition is one of the most potent sources of error, for there is often assent when ideas are not clear and distinct. Volition is also the cause of action and is operative in attention, recollection, and fantasy.

Body-mind relation

Descartes's account of the body-mind relation was not dictated solely by Platonized Christian piety. It was equally the product of his knowledge of science and his convictions about scientific method. First, Descartes was convinced that the body is a machine and that animals' behavior could be explained mechanically, animals having no souls. He was acquainted with the discoveries of William Harvey that showed the circulation of the blood to be a mechanical process. Furthermore, mechanical models were a feature of the age. Decorative fountains were constructed with model men that were moved hydraulically and even uttered sounds like words. Descartes thought that the body contained tubes like water pipes along which the animal spirits (the up-to-date rendering of Aristotle's "connatural spirits") coursed. Because many movements of the body can be executed without conscious intentions, Descartes assumed that these could be explained in the same way as the movements of the hydraulic men. He has thus been credited with the discovery of reflex actions. He thought that all animal behavior could be explained in this way.

Second, Descartes believed in the principle of conservation of energy. The quantity of motion imparted to and conserved in a system being constant, there could be no extra source of energy deriving from volition. Thus, the relationship between body and mind had to be conceived in a way that was consistent with this principle.

Third, Descartes held that scientific explanation consisted of making deductions from relations grasped between clear and distinct ideas. Clear and distinct ideas were available of the simple natures of body (for example, extension, figure, motion) and of mind (thinking, willing) but not of the relation between them. Descartes held fast to the obvious fact that body and mind interact (for when I will, it is my arm that moves; I feel pain when my body falls and not when a stone falls). But we have only a confused idea of this interaction. His account of the relationship between them was therefore only a likely story with which he was not really satisfied. It only narrowed down the point at which the crucial philosophical difficulties occurred.

Descartes knew that muscles operate in opposing pairs and that nerves are necessary for sensation and movement. He pictured nerves as tubes along which animal spirits flow. Changes in the motion of these animal spirits cause them to open some pores in the brain rather than others. When this happens, the spirits are deflected into muscles that move the body by being distended laterally and, thus, shortened. At the level of instinct and habit this process is purely mechanical. At the level of conscious intention, however, something more had to be postulated, the impact of mind on body at the crucial switching point of the spirits, the pineal gland.

Descartes supposed that in sensation motion was transmitted from the stimulus object through a medium to the sense organ and thence along the spirits in the nerves to the pineal gland in the center of the brain, where an impression was made like that of a seal on wax. This was a material image that stimulated the soul to produce a corresponding idea. Descartes gave a similar account of passions in the narrow sense of emotions and organically initiated disturbances, which have their source in the agitation of the spirits. By passions in a general sense, Descartes meant all things that happen to minds, including sensations, lower forms of memory, feelings, emotions, and other disturbances of reason. These he contrasted with the mind's activity. All such incoming stimuli generally give rise to an act of will. Willing again makes contact with the body at the pineal gland, and a chain of events is started in the body terminating with the movement of the muscles, which produces voluntary action.

The soul is like a pilot in a ship in that it can effect the direction but not the amount of bodily movement. Thus, Aristotle's image of active reason could be reconciled with the principle of the conservation of energy. Descartes's hypothesis that interaction between body and mind occurred at the pineal gland did nothing to dispel the philosophical perplexity about how this interaction could be conceived, and then the pineal gland later was shown to be nothing more than an obsolescent eye. Descartes was attached to this idea because the pineal gland was the only part of the brain that was not duplicated in both halves of the brain. He was convinced that the soul, being unitary, could not affect the body at two points. His hypothesis enabled him to keep his mechanistic account of the body intact.

For a long time it has been fashionable to deride Descartes's rather disastrous form of dualism and even to suggest that he created the body-mind problem. This is a piece of intellectual insularity. Descartes was perhaps the first thinker to formulate the problem at all clearly. It would be possible to deny his basic assumption that body and mind are qualitatively distinct substances and still to claim that apart from this metaphysical extravagance his statement of the problem brought out at least two cardinal points that are involved in it. First, he obviously saw the logical incongruity of explaining mental processes, such as geometric reasoning and deliberating before action, in mechanical terms. There is a logical gap between the types of explanation used, as Aristotle had pointed out in his criticisms of the mechanists who held that the soul was moved. Descartes, in his account of the transactions that were alleged to take place at the pineal gland, must have thought that motion at this point is somehow identical or correlated with the mental activity involved in producing an idea or making an act of will. His hypothesis did much to draw attention to this logical disparity between the two types of description.

Second, Descartes's account did much to establish privacy, rather than Aristotle's criterion of purpose with plans and rules superimposed at the level of the rational soul, as the main hallmark of the mental. As has been indicated, Descartes's theory in this respect marked the culmination of a trend that can be traced back through Augustine and Plotinus to Philo. To attribute mind to something is not just to say that men act in accordance with rules and that their movements persist toward ends. It is to say that they act like this because of their knowledge of rules and because they are conscious of ends. Consciousness is crucial for picking out the obvious respect in which men differ from cunningly contrived machines. Descartes must be credited with the clearheadedness to have stood firm on this cardinal point.


Benedict de Spinoza's system was a consequence of pushing Descartes's assumptions to their logical conclusions.

Nature and mind

Descartes had accepted the traditional notion of substance as that which is a cause of itself, can be conceived through itself, and needs only itself in order to exist. Spinoza (16321677) argued that if this is the definition of substance and if there is such a substance, there can be only one such substance, which can be called either nature or God. Nature, so conceived, must have infinite attributes, but we know only two of them, thought and extension. God is therefore "the place of the world and the whole system of thinking." Everything is a mode or modification of God. Thus, nothing can be adequately explained unless its occurrence can be deduced from principles applying to the system as a whole.

Explanation is deductive in character and accords with mechanical principles. Unlike Descartes, Spinoza envisaged a science of psychology in which mental as well as physical phenomena could be deduced from quantitatively expressed laws. Emotions, he argued, must obey laws just as lines, planes, and bodies do. Human beings, as part of nature, must exhibit the general characteristics of all modifications of God or nature. They must be determined within a system; they must have a mental and a physical aspect; and they must exhibit conatus, or the striving to persist within their own being. These characteristics must now be considered in turn.

In stating that human behavior was determined within a system, Spinoza wished to oppose what he considered to be two basic illusions that human beings had with respect to themselves. The first of these was the illusion of free will. People are convinced that they have free will, he argued, because they are conscious of their actions but ignorant of their causes; thus, they conclude that they are uncaused. If stones were conscious, they, too, would believe in free will. Yet human behavior can be explained just as can the movements of stones. In both cases the explanation will consist in deducing what occurs from the laws of the system of which they both are part, ultimately the system of nature as a whole. The human body is a system of simpler elements maintained in an equilibrium, but this system is part of a broader system, not a self-contained isolable system. Adequate explanation is seeing events as part of the whole system of nature; in this system there are no final causes. Nature just is, like a vast, timeless machine.

Body and mind

How then was the body-mind relation to be conceived? Spinoza was one of the first to point to the difficulties in Descartes's pineal gland hypothesis. Spinoza's solution was to suggest that interaction does not take place for the very good reason that body and mind are correlated attributes of the same underlying substance, not distinct substances. Indeed, Spinoza says that the mind is the idea of the body. This is obvious enough at the level of immediate confused ideas that are of bodily states. But the changes in a man's body are part of a larger system, which includes the properties of the food absorbed in nutrition. A wider knowledge of the events in a man's stomach is possible for a physiologist who can understand the laws governing them. He would see these events as part of an ever widening network of events which constitute nature. The man's feeling of stomachache, on the other hand, would be confused, fragmentary, and inadequate, an idea of an effect cut loose from its causes.

This illustrates the difference between what Spinoza called the first and second grades of knowledge. The materials of the first grade are the confused ideas of bodily states that we call feelings and sensations. These ideas are connected only by principles of association. This is the level of sense perception and imagery, of uncritical beliefs founded on animal instinct, association, and hearsay. The second grade of knowledge is rational insight. At this level rational connections are grasped as general notions develop that connect an ever widening system of events. The more abstract and general thought becomes, the nearer it approaches the thought of the Cartesian physicist and, ultimately, God's thought. There is also a third grade of knowledge, called scientia intuitiva by Spinoza, which is more mystical. It is a return from the abstract laws of the scientist to a grasp of the particular as illuminated by such laws. The role of the body, as that which is correlated with mind and of which mind is an idea, seemed to recede when Spinoza passed to reason, or the second grade of knowledge. Mind as the idea of the body becomes at this point almost as difficult a notion as Descartes's notion of mental activity somehow mirroring movement in the brain, for thinking is not of or about body or brain states any more than it is a form of movement which is similar to or identical with brain states.

Conative aspect of mind

Spinoza's account of mental phenomena was much less intellectualistic than that of Descartes. Indeed, in certain respects he reverted to Aristotle's emphasis on teleology and self-maintenance. Spinoza held that the most important characteristic of every modification of nature was its conatus, its striving to persist in its own essence. In man, as in every other natural modification, there is an inherent tendency to react to all changes in a way that maintains its characteristic unity and equilibrium. A person differs from animals in being self-conscious in this endeavor.

Spinoza employed this homeostatic postulate to rewrite Descartes's account of the passions as presented in Les passions de l'âme. Descartes had paid particular attention to the causal influence of animal spirits and had left rather vague the part played by the cognitive grasp of the situation, though he generally put forward an ideomotor theory. Spinoza evinced little interest in the physiology of the matter. Instead, he developed a theory of motivation by harnessing Descartes's passions to his own homeostatic principle. He postulated that whenever a body is acted on by another body, its vitality may be increased, may be diminished, or may remain constant. The awareness of these occurrences is the mental aspect of the psychophysical states which are called emotions. There are thus three primary emotions corresponding to increase, diminution, or maintenance of bodily vitality. These are joy (laetitia ), grief (tristitia ), and desire (cupiditas ). As a result of experience people tend to keep before them what will increase their vitality and remove what will decrease it. "Love" is thus defined as "joy accompanied by the idea of an external cause."

Spinoza drew a sharp distinction between the passive emotions which characterize the first grade of knowledge and the active ones which mark the second and third grades. People are passive when the cause of changes in them lies outside them. In this state of human bondage the emotions that accompany confused, fragmentary ideas are thrust on people; they tend to be sporadic, inordinate, unpredictable, and obsessive. Individuals are subject to panic, jealousy, and overmastering loves and hates. When a man passes to the second grade of knowledge, however, his vitality is increased, and there is a distinctive form of joy that goes with the use of reason. The explanation of human conduct is now to be sought within him, in his clear understanding of the world and of his relation to it. By understanding himself, including his own emotions and history, as part of the system of nature, a man can attain a kind of freedom, which depends upon his acceptance of his own nature. He is then capable of rational self-love and rational benevolence and can attain glimmerings of the greatest good which he can possess"the knowledge of the union which the mind has with the rest of nature." The attainment of this state brings its own delight.

In making suggestions for attaining this state of blessedness, Spinoza in many respects anticipated later psychoanalytic techniques, as well as the general psychoanalytic aim of replacing subservience to irrational promptings by rational control based on self-knowledge. He thought, for instance, that many irrational reactions could be traced back to an early reaction to an object to which the present object had become associated by irrelevant similarities. Scientific understanding of this might help to dissociate the emotion from the irrelevant stimulus. He was not so naive, however, as to suppose that mere intellectual understanding could free an individual from the obsessiveness of emotion. It takes an emotion to master an emotion. And Spinoza thought that seeing things "under the aspect of eternity" had a specific emotional accompaniment. Hence, the psychological shrewdness as well as the ethical profundity of his remark, "Blessedness is not the reward of right living; it is the right living itself. Nor do we delight in blessedness because we restrain our desires. On the contrary it is because we delight in it that we restrain them."


Hobbes (15881679) already subscribed to the deductive model of geometry when he visited Galileo in 1636. He returned replete with concepts and laws that were to form the foundation of his psychology. For the idea had dawned on him, perhaps suggested by Galileo, of applying the new natural philosophy to human behavior. Of course, Epicurus had long ago sketched a mechanical theory of mind, but it was very general. Galileo had worked out the details of a new theory of motion. Could not still further consequences be deduced from the law of inertia? Harvey had deduced the theory of the circulation of the blood from mechanical postulates. Could not Hobbes apply the details of this new theory of motion to psychology and politics?

Body and mind

Hobbes did not really see any particular problem about the relationship between body and mind because for him everything was body. Even God must have a body if he exists, for "substance incorporeal" is a contradiction in terms.

Thus, "conceptions and apparitions are nothing really but motions in some internal substance of the head." Sensation is "some internal motion in the sentient," and pleasure is "nothing really but motion about the heart."

In truth, Hobbes was not much worried by such philosophical niceties as whether, according to his theory, mental phenomena like thinking were being postulated as identical with or merely causally dependent on motions in the head. He was much more interested in working out a mechanical explanation of these phenomena. This is what makes his psychology of absorbing interest. It represents just about the first attempt in the history of psychology to put forward in any detail something that begins to look like a scientific theory.

Mechanical theory of mind

According to Hobbes, in sensation the sense organs were agitated by external motions without which there could be no discrimination and, hence, no sensation. The selectivity of perception was explained by suggesting that while a sense organ retains motion from one object it cannot react to another; similarly, in attention the motion from the root of the nerves persists "contumaciously" and makes the sense organ impervious to the registering of other motions. Imagination was explained by a strict deduction from the law of inertia: "When a body is once in motion, it moveth, unless something else hinder it, eternally; so also it happeneth in that motion, which is made in the internal parts of man, then, when he sees, dreams, etc. Imagination therefore is nothing but decaying sense." This decay is not a decay in motion, which would be contrary to the law of inertia. It comes about because the sense organs are moved by other objects. This explains why dreams are so vivid, for in sleep there are no competing motions from the outside world. Thus, the longer the time that elapses after sensing an object, the weaker the imagination. Memory is imagination with a sense of pastness added to it.

This was an exciting and an ingenious theory. The difficulty about it is that the type of distinction implied in the explicanda cannot really be deduced from the mechanical postulates of the theory, for the differences between perceiving, imagining, and remembering are basically epistemological ones implying standards and criteria different from those that might be attributed to mere movements. Hobbes never faced the basic difficulties that Aristotle first formulated in his opposition to the theory that the soul was itself moved. Nevertheless, Hobbes did produce something that looked like a scientific theory. Its conceptual difficulties attend all psychological theories that attempt to translate epistemological distinctions into differences of process.

Mechanical theory of action

In the theory of action Hobbes attempted to get rid of final causes and to substitute efficient causes for them. To do this, he had to introduce the concept of endeavor, which was very different from Spinoza's conatus. He used the term endeavor to designate infinitely small motions, which he postulated as occurring in the medium between the object and the sense organ, between the sense organ and the brain, and heart. His theory of motivation was that external objects transmit motions by a medium to the sense organs and from there to the brain and to the heart; this results not only in the production of images but also in some alteration or diversion of vital motions round the heart. When these incoming motions help the circulation of vital motions, it appears to us as pleasure, and the body is guided to preserve the motions by staying in the presence of the stimulating object; and conversely with pain. Appetite and aversion are thus the first endeavors of animal motion. They are succeeded by the flow of animal spirits into some receptacle near the "original" of the nerves which brings about a swelling and relaxation of the muscles causing contraction and extension of the limbs, which is animal motion.

Hobbes thought this mechanical account of action was quite consistent with ascribing a central role to consciousness, for in Hobbes's view all action was voluntary in the very strong sense that it is preceded by the thought of an end to be attained. He also claimed that the only way to develop a science of human nature was to look into ourselves and analyze what we find there. Hobbes found two basic motions of the mind, "the one arising from the concupiscible part, which desires to appropriate to itself the use of those things in which all others have a joint interest; the other proceeding from the rational that teaches every man to fly a contra-natural dissolution, as the greatest mischief that can arrive to nature." Everything we do is derived from the desire for power or the fear of death. Conflict between manifestations of these basic motions of the mind leads to deliberation. In this "alternate succession of appetite and fear" the one that emerges triumphant is called "will." "Will therefore is the last appetite in deliberation." Free will is an illusion, for the outcome of such conflicts can be explained mechanically.

Theory of passions

On top of this mechanical ground plan Hobbes superimposed an account of the passions taken largely from Aristotle's Rhetoric. They are to be distinguished by reference to the objects of appetite and aversion as well as by our opinion of attaining such objects. Ambition, for instance, is desire for office; hope is appetite with an opinion of attaining. Individual differences are due, in the main, to differences in the mobility and agility of the animal spirits. Dullness, for instance, derives from "a grossness and difficulty of the motion of the spirits about the heart." Hobbes even had a theory of laughter, which he thought to be the expression of sudden glory caused by something new and unexpected in which we somehow discover ourselves superior to others.

Hobbes assigned a special place in his theory of the passions to curiosity, which, together with the ability to name things and hence to reason deductively, distinguishes humans from animals.

Hobbes's account of the passions was unusual in that it was so positive. For him passions were not, as for the Stoics, imperfect reasonings; they were a particular case of motion in the natural world on which his account of human nature was erected. Nevertheless, when he dealt with what was distinctive of man, his reason, Hobbes parted company with both naturalism and mechanical theory. The type of reason, called prudence, which enables man to satisfy his desires more efficiently, on the basis of experience, must be sharply distinguished from the reason by means of which men are able to arrive at the universal truths of geometry and philosophy.

Scope of mechanical theory

This is not the place to enter into the tortuous details of Hobbes's nominalist theory of meaning or his conventionist theory of truth. It is important to note, however, that in dealing with these specifically human facets of behavior, just as in his treatment of the foundations of civil society, Hobbes defended a position that stressed above all the role of artifice and convention. He even put forward a kind of contract theory of definition to parallel his social contract theory of government. These accounts were underpinned by a very crude causal theory of signs as well as by a mechanical theory of human nature. But no clear connection was ever made between the conventionist and naturalistic elements. David Hume later tried to make such a connection by suggesting that reason was a wonderful and unintelligible instinct in human nature. Hobbes, however, more or less ignored his own mechanical theory when he dealt with geometry, law, logic, and other such artificial creations of human reason.

Thus, although Hobbes was the first thinker to develop in any detail a mechanical theory of mind, he also, more or less unwittingly, exhibited the glaring difficulties in such an undertaking. Indeed, the things in which he was most interested, apart from politics, were precisely those things which it is very difficult to accommodate within a mechanical theory.


Gottfried Wilhelm Leibniz (16461716) understood much better than Hobbes the new natural philosophy; indeed, his discovery of the infinitesimal calculus contributed considerably to it. However, he resisted its mechanistic implications. Descartes had viewed nature, the animal world, and bodies as machines but had stopped short at mind; Hobbes had mechanized mind as well. Leibniz went to the other extreme and mentalized nature. In many respects he reverted to Aristotle.

Nature and mind

The Monadology was a brilliant synthesis of Aristotelian logic taken seriously and a variety of trends in the natural sciences. The whole Cartesian philosophy presupposed the subject-predicate view of judgment in which every proposition, when reduced to logical form, has a subject and a predicate. Moreover, the predicate was thought to be contained in the subject. The Aristotelians thought that this common structure of language mirrored a world of substances composed of various attributes. Leibniz, like Spinoza, took the definition of substance seriously; he thought that it was the cause of itself, could be conceived by itself, and needed only itself in order to exist. But where Spinoza concluded that if this was the definition of substance, there could be only onenamely, God or natureLeibniz concluded that the world must be composed of countless substances all exhibiting the features picked out in their definition. These monads develop according to an immanent principle that is their force or essence. Everything that will ever happen to them, their predicates, is included in their original notion. The principle of sufficient reason explains the succession of these states in time, the identity of a substance at different times being recognized by "the persistence of the same law of the series." Now I am a substance and know by introspection that I am characterized by appetition and perception. What I know about myself must in general be a paradigm for the basic structure of all substances. But no two substances are alike. In perception they all mirror the universe from a particular point of view. There is no interaction, however. Each monad is windowless and develops because of its own immanent principle, not because of external causal influences. The monads seem to influence one another only because of the preestablished harmony of their immanent development.

This bizarre application of an ancient logical doctrine to the world accorded nicely with various new developments in the sciences. Leibniz naturally regarded it as consistent with his discovery of the infinitesimal calculus, the guiding idea of which was that a succession of states develops according to a law governing the series. The successive states of a monad flow into one another like a series of terms differing infinitesimally, their development being defined by the law of the series. This fitted well with the law of continuity, which held that natura non facit saltus ("nature makes no leaps"). Change is a summation of infinitesimal degrees of change. Furthermore, the recent discovery of the microscope revealed that if a piece of cheese or a seemingly empty pool is examined, each will be found to be teeming with life. Could not all nature, therefore, be alivea vast system of monads at varying levels of development? In embryology, too, the doctrine of preformation was in vogue. The assumption that all the characteristics of an adult animal exist in embryonic form from the moment of generation supported Leibniz's view that from the original notion of the monad all its later states and characteristics could be deduced. His conception of the essence of monads being force or activity was connected, too, with his contribution to the dispute in dynamics about the relationship between force and mass. Leibniz held that his concept of vis viva or activity directed toward the future states of the monad was required by his discovery of the conservation of momentum.

The synthesis of Aristotelian logic and these trends in science made Leibniz utterly opposed to the mechanistic picture of nature and of man in which the real world was a world of bodies in motion having only primary qualities whose changes were to be explained only by reference to efficient causes. What is real, he claimed, is not what is mathematically measurable but our experience of activity and perceiving. Nature, as well as man, is characterized by appetition and perception. Final causes are reconciled with the laws of motion by the principle of sufficient reason, which governs the unfolding of the immanent nature of the monads. The difference between substances is only one of degree of clarity in perception and of self-consciousness in appetition. Bare monads have a minimum of perception and appetition. Their perception is confused, and their appetition is blind. Souls, or conscious monads, have memory, feeling, and attention. Animals, or, rather, the dominant monads of animals, are examples. Rational souls, or spirits, are self-conscious; unlike brutes, which are "empirics" and are aware only of particulars, they can reason and understand necessary truths. Extension is only an appearance, the way in which low-grade monads appear to us; the laws of motion are just appearances of the laws of appetition which depend ultimately on God's choice of what is best. Aristotle and Galileo are reconciled, but Galileo's and Isaac Newton's laws are, at best, laws of appearances.

Concept of mind

Leibniz's concept of mind or soul was articulated in what he said about perception and appetition. He regarded perception as marvelous because it cannot be conceived of as an action of the object on the percipient, for the monads are windowless. Perception is better regarded as the expression of a plurality in a unity. One thing may be said to express another when there is a constant and regular relation between what can be said about the one and about the other. It is thus that a projection in perspective expresses its original. The monads are perspectives of the universe from different points of view. Expression is thus the genus of which perception, animal feeling, and intellectual knowledge are species.

Leibniz combined this highly metaphysical account of perception with some shrewd objections to John Locke's tabula rasa theory of the mind. He held that the senses provide us only with instances and by themselves cannot provide the sort of universal knowledge that we have in science. The mind is active and categorizes experience by means of which it interprets the testimony of the senses. The proper analogy for the mind is not a tabula rasa but a block of veined marble. In this doctrine Leibniz harked back to Aristotle's active reason and laid the foundation for Immanuel Kant's categories. Locke, he argued, had in fact tacitly admitted this in postulating mental operations that are known by reflection.

Leibniz maintained that Locke was wrong in saying that the mind does not always think. We have an infinite number of perceptions of which we are not aware. Habituation and wandering attention, as well as the smallness of the perceptions, explain our failure to notice them. Our attention is often drawn to a sound that has just occurred and that we would not otherwise have consciously noticed, although we registered it. "These insensible perceptions are also the signs of personal identity and its constituents; the individual is characterized by traces of his previous states which these perceptions preserve by connecting them with his present state." They are also the means of recollection. They explain decisions that seem arbitrary to us, like turning to the left rather than to the right; they explain frequent feelings of uneasiness which are not intense enough to be felt as pain. These insensible perceptions, he argued, are "as much use in pneumatics as is the insensible corpuscle in physics." Both are beyond the reach of our senses, and there are as good grounds for believing in one as in the other. Since "nature makes no leaps," these insensible perceptions must accord with the law of continuity. "All this brings us to the conclusion that observable perceptions come by degrees from those which are too small to be observed."

Although Leibniz confused some rather different things in this doctrinefor example, unconscious perceptions, minute perceptions that summate like the noise of waves in the roar of the sea, and confused perceptionshe prepared the ground for the concept of unconscious mental processes which was to prove so important in nineteenth-century thought, and he anticipated later investigations of subliminal perception and "determining tendencies." This shows how a highly speculative theory can lead to the emphasis on facets of experience which may be very important but which have previously been disregarded.

Leibniz's emphasis on appetition as the other main characteristic of monads was a welcome change from the intellectualism of Descartes and Locke. However, Leibniz made no detailed empirical derivations from this notion to match the derivations made from his concept of perception. It had more affinities with Spinoza's "conatus" than with Hobbes's "endeavor," although it was really the Aristotelian conception of the formal and final cause brought up to date and made compatible with dynamic theory. His concept can best be elucidated by quoting him; he calls his concept by the Aristotelian term "entelechy," which is "a power mediating between the simple faculty of acting and the definite or effected act. It contains and includes effort. It is self-determined to action, not requiring to be aided, but only requiring not to be inhibited. The illustration of a weight which stretches the cord it is attached to, or of a bent bow, may elucidate the notion."

Soul and body

Leibniz believed that every living creature is composed of a vast number of special organic structures each developing in its own characteristic way; they are all so coordinated and mutually complementary, however, that together they act as an individual. The unity is the soul or the dominant monad; the multiplicity is the body or assemblage of bare monads. The monads of the body all have their own activity, and they are represented or mirrored in the perceptions of the dominant monad or mind. The mind has no power to interfere with or penetrate the forces that it seems to direct. The activities of the monads of the body subserve the dominant activity of the mind as the players of an orchestra, each playing independent parts, subserve the performance of the symphony, and the symphony is the resultant harmony, which has been preestablished. The manifold activities of the bare monads thus combine to bring about the end of the dominant monad. The body depends on the mind in the sense that the reason of what happens in the body is to be found in the mind (compare to Aristotle's view of soul and body).

Thus, Leibniz reverted to a view of mind and nature which was basically Aristotelian, but he transformed the Aristotelian entelechy by giving it the basic hallmarks of Cartesian mindthinking and willing as experienced from within. Furthermore, he pressed the emphasis on privacy much further than Descartes by claiming that the monads are windowless and that everything that will ever happen to them is contained in their original notion.

There was, however, another radically different concept of mind which developed out of Descartes's stress on privacy and incorrigibility as the hallmarks of mental states. This was that of British empiricism, which culminated in Hume and the associationists.


The contribution of Hume (17111776) to psychology was not very extensive in its details because his theorizing about the mind, like that of George Berkeley and Locke, was mainly a way of doing epistemology. And there were special reasons, deriving from his epistemological position, for his eschewing speculation about the relationship between mind and body and the general status of mind in nature. Nevertheless, his general concept of mind was of considerable historical importance. It was the first thoroughgoing attempt to eliminate spiritual substance altogether, and it was the first theory to make reason subservient to the passions and to extol the importance of instinct and habit. It was also the first attempt to develop a Newtonian theory of mind and to erect the principles of the association of ideas into scientific postulatesan undertaking which considerably influenced David Hartley and hence the course of associationist psychology.

Hume's predecessors

John Locke (16321704) took from Descartes the assumption that we are confronted with our own ideas, not with things, and that some kind of certainty is both desirable and attainable. He rejected, however, Descartes's doctrine of innate ideas and adopted a Baconian version of empiricism. He postulated simple ideas of sense that made their imprint on the passive tabula rasa of the mind. Once ideas got into the mind, Locke's theory more or less followed Descartes's, for he believed that the active spiritual substance within intuits relations between ideas, the relations which form the foundations of knowledge. Locke, however, did not stick consistently to his "way of ideas." For example, he asserted, like Descartes, that we have intuitive knowledge about our own existence as selves and "sensitive" knowledge of things existing independently of our perceptions of them. They are material substances that support "powers" to produce in us ideas of primary qualities, which are real properties of the things in question, and secondary qualities which are not real.

George Berkeley (16851753) stuck more consistently to the way of ideas and eliminated material substance, of which we have and could have no idea because it is a logical absurdity; the representative theory of perception; and the distinction between primary and secondary qualities. He claimed, however, that we have "notions," rather than ideas, of ourselves as active agents and of other minds, including God. We also have a notion of our own causal activity. Berkeley relied on this notion to distinguish ideas of sense from ideas of imagination, for having eliminated the concept of a thing independent of our perceptions, Berkeley had to have a criterion for distinguishing what are commonly called things from the mere coexistence of qualities; imaginary objects, for instance, appear to us as clusters of coexisting qualities. Thus, he claimed that when we see objects, it is God talking the divine sense language and producing ideas in our minds; when we imagine objects, we are doing the producing ourselves and have a notion of our own agency in so doing. Berkeley's stress on the activity of the mind contrasted strongly with Locke's tabula rasa.

Hume simply stuck rigorously to the way of ideas and eliminated Berkeley's "notions." There was no simple idea of material substance, of ourselves and others as spiritual substances, of God, or of causal agency. All that was left, therefore, as genuine components of the mind were ideas themselves and certain links between them. Hume likened the mind to a theater "where several perceptions successively make their appearances, pass, repass, glide away," and to a political organization in which the members come and go but the principles of organizationthe principles of the association of ideaspersist.

Hume's contributions

Hume was the first to attempt an explicit distinction between images, which he called impressions, and what we would now call sensationshe called them ideas. He regarded them as two sorts of perceptions. Impressions could not be distinguished from ideas in a Lockian way by their relation to an external object. For Hume, following the way of ideas, disclaimed any possibility of knowledge of a world of objects existing independently of our perceptions. And, because he ruled out notions, Berkeley's appeal to awareness of our causal agency in producing ideas of imagination was not open to him. Of course, like Berkeley, Hume agreed that what we call things exhibit a certain constancy and coherence; they resemble past clusters of qualities. We assume independent existence in order to connect past with present perceptions. But, he argued, we can no more demonstrate the existence of a world independent of us than we can demonstrate that pleasure is preferable to pain.

There are, however, subjective criteria for making the distinction between images and sensations, which is all that remains once belief in a world of independent objects has been ruled out. These are the criteria of vividness and order. Hume suggested that ideas could be picked out because they were faint copies of previous impressions. In other words, impressions are both more vivid than ideas and prior to them. But he gave counterexamples to both these criteriathose of vivid ideas in fever or madness and of forming an idea of a color that had never previously been presented as an impression. In the case of fever or madness Hume suggested that the imagination transfers the vividness of an impression to an idea. Similarly, our belief in an external world is a work of the imagination.

Hume's recourse to the imagination was of cardinal importance in his account of the mind because it linked his theory of knowledge with his rehabilitation of feeling. It has often been remarked that one of the main features of Hume's philosophy was a reversal of the roles hitherto ascribed to reason and feeling. He brought over into epistemology his ethical theory, which he adapted from Francis Hutcheson's theory of moral sense, that moral judgments are based on feeling. "Reason is, and ought always to be, the slave of the passions." This moral sense was the product of biological properties inherent in the species; it had its counterpart in our judgments of matters of fact and existence. Reasoning is "nothing but a wonderful and unintelligible instinct in our souls." Our belief in the reality of causal connections or in the existence of an external world or that the future will resemble the past are instinctive and indemonstrable. "Nature, by an absolute and uncontrollable necessity, has determined us to judge as well as to breathe and feel." The categories used by scientists in their theories, such as continuity and causality, are largely products of the imagination.

Hume stressed facets of human nature that had been largely neglected since Aristotle. He postulated an original fabric of human nature consisting of various propensities not unlike that of later instinct theorists. He also extolled the place of habit in conduct, not simply in explaining such developed forms of behavior as obedience to government but also in explaining the origin of some indemonstrable beliefs. For instance, he held that the idea of causal connection could be analyzed into the elements of priority in time of event A to event B and constant conjunction of event A with event B, together with a conviction of the necessity that B must follow A. As there was no impression of this necessity given in experience, Hume attributed our belief in it to habit or a "determination of the mind" brought about by experience of such constant conjunction and the force of the imagination.

The passions

Appropriately enough, the details of Hume's psychology consisted mainly of an elaborate and highly complex theory of the passions, stated in Book 2 of his Treatise of Human Nature. One of Hume's tasks was to rehabilitate the passions, the natural feelings of decent people, from the Puritans' distrust and the rationalists' disregard. He also had to demolish sophisticated theories, deriving from Hobbes, in which all passions were regarded as forms of self-love. Whereas Bishop Butler attacked psychological hedonism in order to establish the supremacy of conscience, Hume refuted the hypothesis of self-love in order to make way for his rival hypothesis of innate benevolence and sympathy.

He also regarded the sensations of pleasure and pain as part of the original fabric. In a passion one of these sensations is accompanied by an affection. The direct affections include desire and aversion, joy and grief, hope and fear. The difference between these depends on the character of the expectation of good or evil. Desire is for present good, joy for assured good in the future, and hope for probable though remote good in the future. Hume thought that through experience these affections, together with the sensation of pleasure or pain associated with them, can become associated with an object. This generates such indirect passions as pride and humility, when the object is ourselves, or love and hate, when the object is other people. Benevolence and malevolence, however, are not derived from love and hate. Hume classed them as direct and instinctive.

Sympathy occupied a role in Hume's theory of passions somewhat similar to imagination in his theory of belief. The idea of another person's feeling is said to be associated with the idea of oneself, and the required liveliness is thus imparted to the otherwise neutral conception of another person's joy or sorrow.

The idea of the self played an important part in Hume's intricate account of the passions. Like the idea of causality, it presented a serious problem for analysis, for we believe strongly in the reality of both of them. Yet, Hume argued, there was no simple impression of sense from which these ideas derived. Introspection revealed only "some particular perception or other, of heat or cold, light or shade, love or hatred, pain or pleasure." What we call self must therefore be "a bundle of perceptions." Like Locke, Hume then went on to compare the self to an oak, a vegetable, or any type of organism which maintains itself through change by virtue of its relations. Another apt analogy is the self-maintained unity of a political association. But Hume maintained that the unity of this bundle, which makes it a "connected heap," is associative, not real; there are no grounds for ascribing to it the simplicity and permanence which are required for real unity. Perceptions are loose, separate, perishing existences. There can be no real links between them. The problem is to explain how we come to believe that there are.

Hume made the same type of move in relation to the idea of self that he made in the case of causality. He demonstrated that if the way of ideas is followed, there is no ground in experience for believing in the reality of the self; he then embarked upon some speculative psychology to explain how we come to have this belief. He suggested that members of the bundle are related to one another in a specific way in time, the order being preserved by memory. The members have the relations of resemblance and cause and effect between them. But cause and effect is not a real relation; thus, no real unity characterizes the self. We come to believe in it because of the "felt smoothness" with which we pass from one idea to another once the associative links have been established.

Nature and mind

Although Hume's adherence to the way of ideas ruled out wide speculations about the place of mind in nature, there was a highly imaginative idea behind his positivistic system. Hume regarded himself as the Newton of the sciences of humankind. He made frequent references to his pursuit of the experimental method and thought his rigorous interpretation of the way of ideas to be thoroughly consistent with Newton's methodological canons of economy and simplicity in explanation, testability of hypotheses, and refusal to postulate occult causes. Hume stressed that once we have arrived at the original fabric of human nature, it is futile to attempt to satisfy any further our intemperate desire to search for other causes.

But Hume did not emulate Newton merely in his methodology. He also regarded his concepts in the psychological sphere as parallel to Newton's concepts in the physical. His simple impressions were the equivalent of Newtonian atoms, and his principles of association were likened to the "gentle force" of Newton's principles of gravitational attraction. Indeed, Hume regarded imagination and, perhaps, sympathy as cohesive forces. When imagination works according to the associative principles of resemblance, contiguity, and cause and effect, the result is what Hume called the understanding. When it works capriciously, the result is fancy. Of course, the principles of association were as old as Aristotle, though Aristotle's principles were not the same as Hume's. Hobbes, too, had made use of them, though he believed that thought which was guided by desire or which exhibited a plan was more important. However, in Hume's system for the first time they were looked upon as important scientific principles governing the working of the mind. This conception was taken up by Hartley in his theory of vibrations and developed into the associationist school of psychology.

Hume's theory was also important in the history of psychology because it firmly established psychology as the science of the contents of consciousness. Although Descartes's first certainty was rejected in relation to its content, what persisted was the assumption that a man has some incorrigible sort of knowledge about his own mental states. Hume rejected Descartes's search for simple natures, which appear to the mind as clear and distinct ideas, as the foundations of science. Instead, he postulated simple impressions of sense, perishing existences about which we can be certain provided that we make no inferences beyond them. Because Hume, like Locke, consistently confused psychology with epistemology, two parallel traditions developed from his work. On one hand, there was the search in epistemology for sense data which could provide an incorrigible basis for a system of knowledge; on the other hand, there was the development of introspective psychology whose task was envisaged as cataloguing the contents of the mind, analyzing them into simple units, and attempting generalizations about the links between these units which explained the generation of complex ideas and states.

Body and mind

Hume, understandably enough, had little to say about the relationship between mind and body. Body, according to his theory, stood for another bundle of impressions. He did not even connect the idea of self with impressions of bodily states, which might have been an obvious move if he had looked seriously for specific impressions, from which the idea of self is derived. In the Humean tradition William James, for instance, later suggested that the idea of self was intimately connected with impressions of breathing, cephalic movements, and the like. But Hume made no such suggestion. He noted the inexplicability of the fact that "the motion of our body follows upon the command of our will." "Will," he suggested, was another name for the strongest motive (compare to Hobbes's account). But we simply have to accept these de facto connections between events. To speculate further would be to postulate occult causes and thus to sin against both Newtonian methodology and the way of ideas.


It would be very difficult to sketch the contribution of Kant (17241804) to psychology within the framework previously used, partly because he made very little direct and explicit contribution to psychology and partly because his Copernican revolution in philosophy involved a radical reformulation of questions asked under such a framework. Furthermore, though Kant's concept of mind may, in fact, be extremely important insofar as it delimits the sphere of empirical psychology, those who developed empirical psychology in fact paid little heed to the implications of Kant's position. Perhaps that was a pity, for Kant made a sustained effort to separate epistemology from empirical psychology, and until these two are clearly distinguished, there will continue to be confusion in this area, as is demonstrated in the genetic psychology of Jean Piaget. Nevertheless, Kant's influence on psychology was largely negative and indirect; thus, only a short exposition will be given of those parts of his critical philosophy which seem relevant to psychology.

First and foremost, Kant rejected the notion of the empiricists that what is called mind could be explained as the product of ideas arising from experience and systematizing themselves according to laws of association. Kant maintained that the mind must be regarded as a structure regulated by principles of its own activity. These principles could not be arrived at empirically, for they were presupposed by any empirical investigation, including psychology. They could be arrived at only by critical philosophy, which asked the question "What must be presupposed for our experience to be possible?"

Kant was particularly interested in two realms of experienceNewtonian science and the autonomous morality of thinkers of the French Revolution. Kant attempted to reconcile the rationalism of Christian Wolff and Leibniz with the empiricist position of Hume by postulating an active mind whose nature was to impose a structure on experience to make it intelligible. This structure was composed of the categories used by scientists, such as substance, cause and effect, and continuity, which Hume had assigned to the imagination; Kant attributed the structure to reason, which synthesizes the data of sense. The content is provided by the senses, but the form is provided by reason. Thus, what we call nature is in part the work of mind. It is composed ultimately of things-in-themselves, whose real nature must be forever unknowable. We, too, must exist as noumenal selves, as things-in-ourselves. Of course, Hume was right in maintaining that we have no impressions of such selves. At best, we have intimations of such selves behind the appearances in our moral experience as active rational beings.

Human beings have empirical selves insofar as they have bodies and psychic functionsfor example, sensation, imagery, feeling, purposeswhich depend on embodiment. Such selves can be known by inner sense, and their manifestations can be investigated empirically; Kant called such a study anthropology. Kant made his mark on the history of introspective psychology by imposing on these phenomena the tripartite divisionknowing, feeling, and willingworked out in his Critique of Judgment. But he did not note anything particularly novel about the phenomena thus investigated, although he did declare that such investigations could never be properly scientific. He was convinced that science involved quantification and that since the phenomena studied by anthropology could not be subsumed under mathematically expressed laws, psychology could at best be a collection of descriptive material classified under the headings that he suggested. Thus, Kant's extrapolation of Newtonian physics as the paradigm of all sciences had the negative effect of making it incumbent on those who wanted to develop psychology as a science to attempt the quantification of the phenomena to be studied. The result was Gustav Theodor Fechner's psychophysics, Johann Friedrich Herbart's attempt at mathematical laws of consciousness, and countless other premature attempts at quantification.

Another result of Kant's analysis was an increase of interest in the problems connected with the self. The controversy about the existence of a pure self and whether it was a proper object of study occupied most thinkers during the nineteenth century. Of much more importance for psychology, however, was Kant's doctrine that there can be no science of human actions, though its importance has seldom been recognized by those who are committed to empirical psychology. Human actions are the product of human reason, deliberation, and choice, and Kant held that insofar as a man's reason is involved, his behavior is not explicable in terms of the mechanical laws of nature. He acts freely and is determined only by rational laws of his own creation. This was similar to Spinoza's doctrine of freedom and activity. It raises all sorts of problems about the relationship between reason and emotion and between mind and body, problems that Kant did not seriously tackle. His concept of a rational being as a noumenon which was somehow related to a phenomenal embodied self was a metaphysical model that dramatized difficulties connected with the mechanical explanation of thought and rational action which Descartes had used a different model to depict. Kant laid more stress on the concept of will and rational action than did Descartes, but both men picked out a crucial problem for the development of psychology to which no satisfactory answer has yet been given.

Transition from Philosophy to Science

The history of psychology as thus far reviewed is in the main a history of the philosophy of mind, and the issues discussed have been mainly philosophical issues. The rest of the history, however, will be concerned with the slow but progressive disentanglement of psychology as an empirical science from philosophical speculation.

Although it is possible to consider Aristotle's De Anima as the transition from presystematic to systematic psychology, the transition from philosophy to empirical science cannot be pinpointed so precisely. This was not so much a transition as a process of differentiation. Indeed, it began with Aristotle, but it becomes unmistakable in the psychologies of Descartes and Hobbes, both of whom were affected by the impact of Galileo's physics. Both framed hypotheses about the physical and physiological mechanisms of consciousness and behavior that were in principle testable by observation and experiment. From Descartes and Hobbes the main line of development in empirical psychology was through the British empiricists Locke, Berkeley, and Hume.

eighteenth-century british psychology

Locke's new way of ideas laid the foundations for the twin doctrines of sensationism and associationism. The theory was that the mind is composed only of sensations and mental images (mental images being faint copies of sensations), that all complex percepts or ideas are formed through association, and that all trains of thought arise through association. Locke's analysis of mind was not so simple as that. He included ideas of reflection, abstract ideas, and the self, or possessor of sensations and ideas. Berkeley contested the existence of abstract ideas and furthered the development of associationism by giving an associationist explanation of the perception of the third dimension of spaceanother hypothesis that was to become the subject of experimental study. Hume further refined sensationism by eliminating the self on the basis of the negative result of his attempt to observe it by introspection. The next important step was taken by Hartley, who proposed a neural basis of conscious processes. His hypotheses, too, could in principle be tested by observation and experiment. Further refinements and elaborations of associationism are to be found in the works of James Mill, J. S. Mill, Thomas Brown, and Alexander Bain. The associationist doctrines spread to the Continent and as experimental psychology later returned to England and went to the United States.

A second major influence on the advance of psychology toward the status of an empirical science was provided by the biological sciences, notably in the evolutionary doctrine of Darwin. This influence was later to prove one of the causes of the disruption of associationist psychology.


While David Hartley (17051757) was practicing medicine, he made many observations of psychological interest and wrote his major opus, Observations on Man, His Frame, His Duty, and His Expectations (1749). It was a thoroughgoing attempt to provide a neurophysiological basis for the mental processes of sensation, imagery, and association. Influenced by Newton's Opticks, he proposed an explanation of conscious experience and association in terms of vibrations transmitted through nerves, which were conceived of as solid fibers, thus breaking from the earlier conception of nerves as hollow tubes for the conduction of the animal spirits. For every kind of sensation there are different kinds of vibrations or vibrations differently located; corresponding to images or memories, there are vibratiuncles, miniature vibrations that can persist after the larger vibrations have subsided and which form the physical substratum of memory. The associative processes occur by virtue of the fact that if two stimuli occur simultaneously and produce two corresponding vibrations in two regions of the brainsay, vibration A arising from a visual stimulus and vibration B arising from an auditory stimulusthe repetition of only the visual stimulus producing vibration A will arouse vibration B in the absence of the original stimulus that produced B. This is a simple translation into neurophysiological terms of the traditional principle of association of ideas, explaining, for example, the association of thunder with lightning. Hartley further advanced associationist theory by suggesting ways in which some of the several special laws of associationcontiguity in space, contiguity in time, contrast, and similaritycould be reduced to the single law of association by temporal contiguity. He also offered a more detailed account than had yet been given, in terms of association, of the formation of general ideas.


As professor of moral philosophy in Edinburgh, Thomas Brown (17781820) delivered a series of lectures subsequently published under the title Lectures on the Philosophy of the Human Mind. Though not himself an associationist, he made very important contributions to the theory of association, which he preferred to describe as suggestion. Two of his ideas were of especial importance. First, he distinguished between simple suggestion, which is association in the commonly accepted sense, and relative suggestion, which is not in any sense an associative process but is a process that was later to be described by Charles Spearman as the "eduction of relations." Second, Brown formulated the secondary laws of associationthe principles of recency, frequency, duration, liveliness, and so on. These were later to become the subject of innumerable experimental studies.

nineteenth-century british psychology

Brown's philosophy was severely criticized by Sir William Hamilton (17881856) in his Discussions on Philosophy and Literature (1852) and his Lectures on Metaphysics and Logic (posthumously published in 18591860), but Brown was defended with no less force by J. S. Mill in An Examination of Sir William Hamilton's Philosophy (1865). Hamilton, who was professor of logic and metaphysics at Edinburgh from 1836 until his death, had been greatly attracted by German philosophy and contributed to the rise of the British idealistic school of philosophy later to be represented by T. H. Green and F. H. Bradley. This school, deriving its inspiration from the intellectualist and idealist thought of G. W. F. Hegel and other Continental philosophers, had no common ground with the mechanistic empiricist and physiological approach of the British psychologists, but in its criticism contributed to the refinement, as well as the demise, of associationism. It was Bradley who, in attacking the atomistic features in associationism, phrased the dictum "Association marries only Universals." This theme was to be developed in an original way in G. F. Stout's doctrines of noetic synthesis and relative suggestion.

James Mill and John Stuart Mill

Associationism reached its zenith in the work of James Mill (17731836). An economist and historian rather than a philosopher or psychologist, he learned his philosophyhedonistic utilitarianismfrom Hartley. His psychology, however, was a refinement of Hartley's and his analysis of mind was much more acute. The Analysis of the Human Mind appeared in 1829. Mental life was reduced to sensory elements, and the development of complex ideas was explained by the principle of association. Mill gave a clearer account than had Hartley of the way in which the several laws of association could be reduced to the single law of contiguity. He refined previous accounts of emotional experience in terms of sensations. Like Hartley, he attempted to apply the principles of associationism to the explanation of the complex phenomena of conscience and religion.

John Stuart Mill (18061873), his son, was a more subtle and acute philosopher than his father. He was certainly more disposed to take seriously any objection to a theory he wished to defend. In his rational and reasonable way he was inclined to make concessions that resulted in his rejecting the original theory. He sacrificed simple hedonism by conceding that pleasures might differ in quality. He gave up associationism by introducing the concept of mental chemistrythe idea that mental compounds, like chemical compounds, might exhibit properties not deducible from the properties of the elements. This breach in the associationist defenses was to be widened later by doctrines of creative synthesis and Gestalt qualities and the biological concept of emergent evolutionideas all at variance with pure associationist doctrines. J. S. Mill was less concerned with sensationism as a psychological doctrine than with its philosophical counterpart, phenomenalismthe description of material things and the physical world in terms of sense data or "permanent possibilities of sensation."


Though in the associationist tradition, Alexander Bain (18181903) was less interested in the philosophy of mind than in psychology as an empirical science. He was emphatic in his demand that psychology should be cleared of metaphysics. His Manual of Mental and Moral Science (1868) was virtually a textbook of empirical psychology. It was a condensation of his two major works, The Senses and the Intellect (1855; rev. ed., 1894) and The Emotions and the Will (1859). He was thoroughgoing in his insistence on the need for a physiological basis for psychology not merely in general terms but in terms of known physiological facts, about which he made it his business to be well informed. As far as this implied a philosophy of mind, it found expression in his formulation of the principle of psychophysical parallelism. Especially important were his accounts of habit formation and learning. His treatment of habit was in large measure the inspiration behind the eloquent chapter on this topic in William James's Principles of Psychology. E. L. Thorndike and other "learning theorists" owe to Bain the first clear formulation of the law of effect, the principle that responses are ingrained by the reward of pleasure. Even his sillier theories contributed to enlightenment. One of the silliest theories in the history of psychologythat maternal love is based on the pleasurable tactile sensations experienced from contact with a babyforeshadows the subtler theories of Freud concerning erogenous zones in the body and, more remotely, the "releaser mechanisms" of the ethologists. Bain's associationism was not an ideology. It was merely that he had assimilated the dominant features of the current psychological climate of opinion.

Two other developments were to complete the transformation of psychology from a branch of philosophy into an empirical science: (1) the impact of the theory of evolution and (2) the establishment of laboratories for experimental psychology. The theory of evolution had its origin in England in the work of Darwin; the idea of laboratories for experimental psychology came chiefly from the Continent.

evolutionary psychology

Darwin's theory of evolution as set out in his Origin of Species (1859) was a very large theory, but it was a scientific, not a philosophical, theory. It was supported by an enormous body of empirical observations. Theories of evolution date back to antiquity. Charles Darwin's grandfather Erasmus Darwin had adumbrated a Lamarckian theory of evolution. Alfred Russel Wallace anticipated Darwin's theory by a few months. Herbert Spencer (18201903), who had propounded philosophical and psychological theories of evolution for some years before the appearance of the Origin of Species, was accordingly well placed to capitalize on Darwinism in the development of his own ambitious "synthetic philosophy."

Darwin (18091882) himself wrote on distinctively psychological topics. His Descent of Man (1871) discusses the similarities between the mental processes of man and of animals. His work Expression of Emotions in Man and Animals gives an evolutionary interpretation of changes in features and postures and assigns biological utility to these changes. The evolutionary approach stimulated many studies by amateur and professional naturalists. G. J. Romanes (18481894) collected evidence for the continuity of development from the animal to the human mind, and Sir John Lubbock (18341913) was among the first to use laboratory techniques in the study of insects. Laboratory studies like these were to be developed later on a grand scale by such American comparative psychologists as E. L. Thorndike and R. M. Yerkes.


Sir Francis Galton (18221911), the versatile cousin of Charles Darwin, contributed to meteorology, anthropology, anthropometry, and psychology and to the development of statistical and other metric methods in psychology. Among his major interests was the inheritance of mental characteristics, for the study of which he devised ingenious methods. He stressed heredity as a determinant of mental life and behavior. His records of the behavior of twins are reminiscent of the Leibnizian concept of a preestablished harmony. According to his records, twins can behave exactly like two clocks each causally insulated from environmental influences and from each other, behaving similarly and thinking in unison almost entirely in consequence of the similarities of their innate constitution. His major psychological works were Hereditary Genius (1869) and Inquiries into Human Faculty (1883). He set up the first two English psychological laboratoriesthe first at the International Health Exhibition of 1884 and the second in the South Kensington Museum. He pioneered the application of physical and psychometric tests in schools.

Ward and Stout

Philosophical psychology was to feel the impact of the new biological approach. James Ward's revolutionary article on psychology in the ninth edition of the Encyclopaedia Britannica (1886) mounted a devastating attack upon associationism, recasting psychology in terms of a "psychoplasm," or "presentational continuum," which, like bodily tissues, undergoes progressive differentiation and integration. Ward's distinguished pupil Stout wrote Manual of Psychology, a standard text for some three decades, in 1898. This was described as being written from a genetic point of view; thereafter, almost every textbook of psychology had a biological orientation.

empiricism in europe

The empiricist philosophy was introduced into France by littérateurs and essayists like Voltaire and Denis Diderot, not by philosophers or psychologists. Voltaire had lived in England from 1726 to 1729, and so was in a position to introduce British ways of thought in philosophy into the intellectual life of France. Diderot had a clearer understanding of British empirical psychology. He particularly interested himself in the mental life of persons deprived of one sensefor example, sight.

The first of the French empiricist philosophers to contribute to sensationism was Étienne Bonnot de Condillac (17151780). Diderot had been concerned with the mental life of persons deprived of one sense; Condillac started from the imaginary case of a person deprived of all senses except one. He took the case of a statue endowed only with the sense of smell, selecting smell because of its relative simplicity. From this he proceeded to add other senses and to explain in sensationist terms attention, memory, imagination, and reason. He attached no importance to association. He believed that the experience of one sensation after another is ipso facto a comparison of the two and that the occurrence of the unpleasant sensation constitutes the will to terminate the sensation. Condillac's sensationism was perhaps the simplest and most elegant form of the doctrine in the history of psychology. His views are set out in the Traité des sensations (1754).

Claude-Adrien Helvétius (17151771), author of a volume of essays titled De l'esprit (1758), was a minor social and political philosopher who seized upon Locke's empiricism and concept of the tabula rasa to defend an extreme doctrine concerning the equality and perfectibility of men. His basic thesis was that all differences between men are due to differences in experience and education. All error was due to passion or ignorance.

The doctrines that Helvétius derived from Locke were to return to England in the works of William Godwin, especially in his Political Justice (1793). Like Helvétius, Godwin taught that all men are equal at birth and that their subsequent differences were due to experience and education. Voluntary actions originate in opinions, which can be changed by rational persuasion. Vice is error, which can be corrected. In Helvétius and in Godwin the association of empirical philosophy with an intellectualist hedonism is displayed in its most extreme form.

Through Condillac the influence of Locke spread to Italy and Switzerland. In Italy this influence is to be seen in the teachings of several all-but-forgotten writers. In Switzerland, Charles Bonnet (17201793) of Geneva was the outstanding figure in empirical philosophy. His chief work in psychology was the Essai analytique sur les facultés de l'âme (1760). Although he followed Condillac for the most part, Bonnet differed chiefly in the importance he attached to physiological explanations.

german psychology and experimentation

Throughout the seventeenth, eighteenth, and early nineteenth centuries German psychology was dominated by the philosophical doctrines of Leibniz, Kant, and Hegel, each of whom contributed to a rationalist idealism very unfavorable to the development of psychology as a science.


Georg Wilhelm Friedrich Hegel (17701831) has received scant attention in the histories of psychology, understandably so since his form of rationalism is the most extreme antithesis to the empiricist philosophy that had favored the development of psychology as an empirical science. He is, however, not without importance in the history of psychology.

One of Hegel's theses was that it is a mistake to suppose that complex phenomena are explained only by reference to simpler phenomena, that we can, for example, understand religion in its developed form by the study of cults of primitive people or that we can understand man only through the study of lower forms of animal life. In this he challenged what had long been and still is a basic principle of comparative psychology, but Hegel's thesis survives in the view of psychologists who hold that the proper study of humankind is man and that we should begin with civilized man in advanced societies. It lives on in the contention of Freudian psychologists that the evidence for infantile sexuality can be appreciated only in the light of adult sexual behavior.

Equally important for psychology is the Hegelian dialectical progressionthesis, antithesis, synthesis. When this progression is stated as an empirical observation of movements of thought and action, not as a metaphysical principle or a principle of logic, it illuminates many sequences in the history of politics, philosophy, and science. A dialectical progression is illustrated in the fate of Hegel's own philosophy. Its influence in Germany was short-lived. His rationalistic thesis issued in an empiricist antithesis, Wundtian experimental psychology. The dialectical progression is illustrated by the British vogue for Hegelianism among philosophers who found in it an antithesis with which to confront the prevailing empiricist philosophy and psychology. The progression is illustrated by the sequence from Hegel's idealist thesis to the antithesis of dialectical materialism that was to become a central tenet of communist philosophy. Although it provides no comprehensive philosophy of history, the concept of dialectical progression affords a rather more subtle and articulate account of historical movements than conventional, commonsense accounts in terms of "the swing of the pendulum."

Hegel's doctrines were associated with, and conferred philosophical status upon, a widespread romantic and mystical philosophy of nature according to which everything in nature had some spiritual and symbolical significance. The influence of this philosophy of nature persisted far into the nineteenth century and in the biological sciences favored vitalistic, as opposed to mechanistic, accounts of mind, body, and nature. Psychologists divided progressively into two groups. The first comprised the philosophersthat is, those who primarily taught philosophy and whose philosophy of mind contained much metaphysics. The second group consisted of natural scientists whose approach was from mathematics, physics, and the biological sciences. The distinction is not sharp, since romanticism and metaphysics were in the air that every German student, even students of the natural sciences, breathed.

The first steps in the transition from the philosophy of mind to scientific psychology were taken when Kant challenged psychologists to show that their subject could claim scientific status. This challenge was taken up by Herbart, Ernst Heinrich Weber, and Fechner. That it could be an experimental science was argued by Weber, Fechner, Johannes Müller, Hermann von Helmholtz, and others. Wundt finally established it as a science that required a distinctive kind of laboratory.


Johann Friedrich Herbart (17761841) set out to establish a basis for psychology other than that of the prevailing "faculty" psychology associated with Christian Wolff (16791754), a disciple of Leibniz and precursor of Kant who was much less distinguished than either. Herbart tried to show that the laws describing mental process could be put into precise mathematical form. Herbart's first achievement was the grafting of associationism onto a rationalist metaphysical root. The soul was retained, serving the traditional function of giving unity to the mind, but the data of empirical psychology were, as in associationism, sensations and ideas. In Herbart's system ideas were not just passively associated. They interacted by attractions and repulsions in accordance with which they were drawn into or forced out of consciousness. The behavior of ideas in Herbart's psychology resembles that of the "reals" in his pluralistic metaphysics. Two "reals"for instance, A and B differing in quality, tend to disturb each other because of their difference, but each also tends to preserve itself by resisting the disturbing effect of the other. This principle of self-preservation is reminiscent of the Spinozistic doctrine that "everything that is in itself endeavors to persist in its own being" and, when applied in Herbart's psychology, foreshadows the concept of homeostasis that was to be current in psychology a century later.

Herbart's account of the way in which ideas enter consciousness and are expelled from it represents a phase in the history of the theory of the unconscious midway between Leibniz and Freud; his concept of the apperceptive mass, a system of ideas bound together by mutual attraction, was still current when psychoanalytic writers were developing the concept of a mental complex. Herbart's metaphysics and mathematics were to be forgotten, and he did not contribute directly to the development of psychology as an experimental science. His most lasting influence was in the field of educational psychology, chiefly in the application of his theory of apperception to the process of learning.


Rudolf Hermann Lotze (18171881) succeeded Herbart in the chair of philosophy at Göttingen. His most influential work was his Medizinische Psychologie (1852), the first systematic work on physiological psychology and one of the very few written by an author qualified in both physiology and philosophy. Against the then prevailing view he defended the thesis that every mental phenomenon has its physiological counterpart and that the laws which apply to inorganic matter also apply to organic matter. Final causes, vital and mental forces, and the soul itself can act only through mechanical causation. He insisted, however, that physiology alone cannot explain mental phenomena. Lotze is best known in psychology for his doctrine of local signs, a contribution to the theory of space perception.

Weber and Fechner

Experimentation and the use of quantitative methods in psychology were greatly advanced by Ernst Heinrich Weber (17951878) and Gustav Theodor Fechner (18011887), who were colleagues in the University of Leipzig and who both taught Lotze.

Weber taught anatomy and physiology. His early work De Tactu (1834) reported studies demonstrating the difference between muscle sense and touch. These studies were extended to pain, pressure, and temperature, through which emerged the concept of thresholds and the famous law that has come to be called Weber's law. This states that the smallest increment in a stimulus required to produce a difference in the sensation experienced is not an absolute amount but is relative to the magnitude of the stimulus in question. Like most German scientists of his time, Weber was to some degree under the spell of the current metaphysics and the romantic philosophy of nature, but neither of these influenced his experimental studies. His metaphysics and his science were kept apart.

With Fechner the case was different. Fechner's intellectual life was a pilgrimage from physics and chemistry, through physiology and medicine, to metaphysics and mysticism. From an early age he had been preoccupied with the problem of the relation between matter and spirit. He was attracted to a form of panpsychism according to which not only man and the lower animals have consciousness but also the earth and the other planetsindeed, all material things. In this view all souls are parts of the soul of the universe.

Fechner concluded, on the obscurest of grounds, that the mystery of the relation between mind and body would be resolved by ascertaining the quantitative relations between stimuli and sensations. He suggested that Weber's law could be put into a quantitative form. Weber's law thus became the Weber-Fechner law, according to which the relation between stimulus and sensation is expressed in the formula S = k log R where S is the experienced intensity, R is the physical intensity, and k is a constant for the particular sense in question. For the verification of this law Fechner designed what are known as the psychophysical methods. These methods have been used in the most tedious of laboratory exercises to which many generations of students of experimental psychology have since been subjected, and the published results of these exercises are among the most tedious controversies in the history of science. But the possibility of experiment and measurement in psychology was establishedparadoxically, by a metaphysical mystic. The metaphysics and the mysticism were soon forgotten, but the exercises live on.


Friedrich Eduard Beneke (17981854), a contemporary of Herbart, was another philosopher who contributed to the foundation of a science of empirical psychology, which, he claimed, was the basis of all philosophy. Like Herbart, he set out to provide a basis for psychology other than that of a doctrine of faculties, and like Herbart, he stressed the activity of the mind. Among his works on psychology are Lehrbuch der Psychologie (1832) and Die neue Psychologie (1845). Because of his rejection of the prevailing Hegelian philosophy of the Absolute, Beneke was dismissed from his post in the University of Berlin, but after Hegel's death he was reinstated. His best-known contribution to psychological theory was his doctrine of mental, as contrasted with physiological, traces for the explanation of the facts of memory. This doctrine was later to be developed in Great Britain by Stout.


Johannes Müller (18011858) was a contemporary of Beneke at Berlin. He was the first to hold the title of professor of physiology. (Hitherto, the subject had been taught as a branch of medicine.) He had been under the influence of the prevailing philosophy of nature but contributed to the clarification of the concepts of mind, body, and nature by distinguishing the mental principle, which is restricted in its operation to the nervous system, from the vital principle, which is diffused throughout the organism. He was also preoccupied with the opposition between nativistic and empiricist explanations of space perception as represented, respectively, in the doctrines of Kant and Herbart. Müller reformulated the issue in terms that made it possible to submit the question to experimental tests. He also formulated the theory of specific energies in the nervous systemthe hypothesis that the sensory qualities are generated by specific activities of the organs of sense or by specific differentiation in corresponding realities in the brain.


Hermann von Helmholtz (18211894), Müller's distinguished pupil, is acknowledged to be the most outstanding of the physicist-physiologists who have contributed to the development of experimental psychology. In the range of his pioneering studies he has been compared with Francis Galton. His publications were more numerous than Galton's, and his investigations were carried further. He was the first to make a realistic calculation of the speed of nervous impulses, which are important, among other things, in the study of reaction times. He developed Müller's doctrine of specific energies and Thomas Young's three-color theory of vision.

Helmholtz's Handbuch der physiologischen Optik, published in three volumes (18561866), remained an authoritative text for many decades, although it was not translated into English until 19241925. No less outstanding were his contributions to the theory of hearing and the related subjects of phonetics and music. He was essentially a scientist with little interest in philosophy and still less patience with transcendentalism. There is, however, much in his writings of philosophical interestfor example, his puzzling concept of unconscious inference in perceptual judgments. His discussions of the principle of the conservation of energy are important in the history and philosophy of science.


The last phase in the transition of psychology from a branch of philosophy to psychology as an independent empirical science is conveniently dated as beginning in 1879, when Wilhelm Wundt (18321920) established the first psychological laboratory. Wundt's chief claim to a place in the history of philosophy arises from the conceptual system in terms of which he interpreted the experimental data from his own and other laboratories. His philosophy of mind deviated from the simpler forms of atomistic sensationism in that the ultimate elements of mind were, according to him, of two kinds, sensations and feelings. He and his disciples devoted much energy and skill to defining the differences between sensations and feelings and to elucidating his curious tridimensional theory of feeling, but the general program was to analyze experience into its elements, to define the fundamental attributes of these elements, and to formulate the laws in accordance with which these elements are combined. The account leaned heavily on the principle of association but deviated from traditional associationist doctrines in introducing a concept of creative synthesis. This concept was a variant of the concept of apperception and embodied a theory of attention. It had some points in common with J. S. Mill's conception of mental chemistry and in some degree foreshadowed later theories of emergent properties and the doctrine of the Gestalt psychologists that a complex experience is more than the sum of its parts. His most influential work was Grundzüge der physiologischen Psychologie (1873). In later years he published two works that contributed to the incursion of psychology into sociology and anthropology.

Ebbinghaus and Külpe

Among other outstanding experimental psychologists were two of Wundt's pupils, Hermann Ebbinghaus (18501909) and Oswald Külpe (18621915). Wundt's laboratory research had been chiefly concerned with sensation and perception and with relatively simple processes of reaction and association. Ebbinghaus and Külpe extended the experimental method into the study of the higher and more complex functions of memory and the processes of thinking.

In a monumental work, Über das Gedächtnis (1885), Ebbinghaus published the results of what has been described by J. C. Flügel in his A Hundred Years of Psychology as "the most brilliant single investigation that has ever been made in experimental psychology." Ebbinghaus's outstanding achievement was to extend the experimental method to the "higher thought processes." He was the first to establish quantitative laws concerning the process of memorization. In 1894 he succeeded Theodor Lipps, a pupil of Wundt's most widely known for his studies in psychological aesthetics, in the chair of psychology at Breslau. There Ebbinghaus pioneered in the study of intelligence and devised the completion test, which remains an important component of intelligence tests.

Külpe directed the laboratory at Würzburg, which achieved great fame through its investigations of willing and judging. Through the discovery of imageless thoughts these studies contributed both to the breakdown of sensationism and, in consequence of the inconclusive disputes this discovery provoked, to the behaviorist revolt against introspective methods. At Würzburg as at Leipzig confusion arose through the interpretation of experimental data in terms of implicit philosophical concepts and assumptions, and the conclusions drawn have had to wait for review in the light of further clarification of the distinction between empirical psychology and the philosophy of mind.

the shift to the united states

In the age of Wundt, psychology was a Germanic science, and Germany was the heart of the empire. Mainly through Wundt's influence upon those who came to Leipzig from the United States, psychology became an American science with the United States as the new seat of dominance. Among those who studied abroad and then returned to America were Stanley Hall, who established the first American psychological laboratory at Johns Hopkins in 1888; J. McKeen Cattell, who after several years as assistant to Wundt founded the laboratory at Pennsylvania; and Hugo Münsterberg, who, having established a laboratory at Freiburg, was invited by William James to Harvard in 1892. In the same year E. W. Scripture took charge of the laboratory at Yale. By 1897 there were fifteen psychological laboratories in the United States, and by the end of the century there were twenty-six, all based, to begin with, on the laboratory in Leipzig. Most of Wundt's American pupils, however, were soon to deviate from the German pattern and to open up approaches characteristically Americanallergic to philosophical speculation, distrustful of introspective methods, and much concerned with the practical applications of their science. Hall became famous for his studies of adolescence. Cattell, more influenced by Galton than by Wundt, concentrated on the measurement of individual differences. Münsterberg's interest turned to applications of psychology to industry and criminology. The mantle of Wundt fell upon E. B. Titchener, an Englishman from Oxford who after his studies at Leipzig went to the United States to develop experimental psychology at Cornell.

the established order of 1900

Wundtian psychology was one important form of and ingredient in what has been called the established order of 1900, against which many revolts were to be mounted. There were, in fact, at least two established orders, one in Britain, represented by Ward and Stout, and the other in the United States, represented by Titchener. These were very different establishments, but they had in common a foundation in some form of body-mind dualism and the acceptance of the facts of consciousness, observed by introspection, as defining the subject matter of psychology.


James Ward (18431925) presented his own system as a sort of synthesis of the too objective thesis of Aristotle's psychology and the too subjective antithesis of Descartes's psychology. His basic conceptual framework was doubly tripartite. In his analysis of experience he distinguished the three modes of consciousnesscognition, feeling, and conation; his analysis of each kind of experience referred to a self or ego, an act or mental attitude, and a presentation (a mental object, sensation, or idea). The most interesting features of his system are contained in his detailed analysis of the phases of development from simple sensation to perception and from perception to the construction of a memory thread and an ideational tissue. Though qua psychologist Ward can be treated as a dualist, his background metaphysics was a variant of an idealistic monadology of the Leibnizian type.


G. F. Stout (18601944) developed Ward's psychology in an individual way, creating an original and independent system. As a psychologist Stout, like Ward, developed a dualistic psychology, but as a philosopher he developed an original theory of mind, body, and nature.


E. B. Titchener's laboratory at Cornell was the temple of the Wundtian form of the established order, and Titchener (18671927) was its high priest. Here as elsewhere, however, empirical psychology continued to be inextricably entangled with philosophy. Titchener's deviations from sensationist and associationist psychology were less fundamental than he himself believed. He was a dualist, and he confessed to a bias in favor of sensationism. He was reductionist in his treatment of conation. He differed from the classical sensationists in accepting feelings as basic elements; he also differed from them in the treatment of the elements as existences, as contrasted with meanings. He sought to explain complex mental states as arising from the synthesis of elements and thus to display the structure of the mind. Accordingly, he is described as a structural, as opposed to a functional, psychologist. His cardinal tenet, which was to become the major object of attack, was his thoroughgoing proclamation of introspection as the distinctive method of psychology. His two most important works were his Lectures on the Psychology of Feeling and Attention (1908), a detailed exposition of the thesis that "the system of psychology rests upon a threefold foundation: the doctrine of sensation and image, the elementary doctrine of feeling and the doctrine of attention," and the Lectures on the Experimental Psychology of the Thought (1909), an equally thoroughgoing examination of the claims for the discovery of an imageless thought element and a polemic against the doctrine of Franz Brentano and Stout that references to object is the criterion of mind.

revolts and the era of the schools

The established order of the United States and the established order of Britain were to become the objects of attack from four directions: (1) The behaviorist attack directed in the main against dualism, the concept of consciousness, and the reliance upon introspection; (2) the attack of the Gestalt psychologists against all forms of psychological atomism; (3) the psychoanalytic attack against the overemphasis on conscious processes and inadequate recognition of the unconscious mind; and (4) the attack of the hormic psychologists, which was directed against the intellectualism of traditional psychologythat is, the overemphasis on cognitive processes and the relative disregard for conation or purposiveness in the explanation of conscious experience and behavior.

In the four revolts the schools were all fighting on more than one front. Each was attacking traditional psychology, and each engaged in polemics with the other revolting schools. Confusion was increased by the fact that within each school there were conflicting factions and by the general failure to distinguish straight empirical issues from issues of philosophy and of linguistic usage.


The conception of psychology as the study of behavior and as an essentially biological science dates back to Aristotle, but behaviorism as an ideology can be dated precisely. It began in 1914, when J. B. Watson (18781958) published Behavior while a professor at Johns Hopkins University.

This book was a protest and a revolt against dualism, the concept of consciousness, and any use of the introspective method in psychology. Psychology is to be the study of behavior by objective methods. It was a protest in defense of animal psychology, in which statements about the animal mind and the consciousness of animals must be pure guesswork, and it was a protest against the interminable and inconclusive disputes between introspective psychologists about the differentiation of sensations and feelings, the James-Lange theory of emotion, and imageless thought. It was also an attack on the traditional theory of consciousness in which some sort of mental stuff was thought to be the subject matter of psychology.

In Behavior and two other important books, Psychology from the Standpoint of a Behaviorist (1919) and Behaviorism (1924), Watson developed his distinctive account of all the major topics that constitute psychology. Like the structuralists he set out to exhibit complexes in terms of simple elements, complex responses to situations as derived from simple responses, native and acquired. The analysis of behavior was in terms of stimulus and response (an analysis to be elaborated later by E. C. Tolman in terms of intervening variables). Sensation and perception were described as responses to present stimuli and constellations of stimuli, memory and learning as responses to past stimuli and neural traces, feelings and emotions as types of sensorimotor responses, and thinking as subvocal verbal behavior. Introspection itself was redescribed as verbal behavior. In his system Watson included much that was irrelevant to the major principlefor example, a bias toward explanations in terms of environmental influence and a bias against explanations in terms of heredity. He had a special bias against the concept of purpose, though later behaviorists found no difficulty in assimilating purposive behavior as goal-directedness. His laws of conditioning were the old laws of association transformed into generalizations about bonds between simple reflexes instead of between simple ideas.

Watson's writings were naive and often confused, but his behaviorism sailed on the tides of the time. Behaviorism was inevitable. Watson's behaviorism was fortunate in that it was reinforced by the most important philosophical movements of the period, positivism and physicalism. It was also reinforced by the logicians and the methodologists of the inductive school, who maintained that scientific laws state correlations between observables. Watson accordingly assumed that because mind was unobservable, it could not be discussed or referred to in science. When logicians later began to proclaim that scientific systems were hypothetico-deductive, such behaviorists as Tolman and C. L. Hull conceded the importance of unobservables in the form of intervening variables and hypothetical constructs. This return to the methodology of Galileo made any simple form of behaviorism difficult to maintain. Nevertheless, B. F. Skinner stuck to the old inductive concept of scientific method and proclaimed that his findings involved no theory. Behaviorism was further supported by a number of outstanding experimental psychologistsfor example, K. S. Lashley and W. S. Huntersympathetic to Watson's approach.

Lashley was primarily a neurophysiologist who as a behaviorist was more sympathetic to the views of the Gestalt psychologists than to those of Watson. He contributed in an important way to the advance of knowledge concerning the localization of the higher functions in the cortex.

Hunter, a distinguished experimental psychologist, rallied to the support of behaviorism through an odd philosophical argument, based on a very naive form of realism, that consciousness or experience is merely a name applied to what other people call the environment. This argument is reminiscent of a characteristic doctrine of Ward and Stout that the subject matter of psychology comprises "the whole choir of heaven and earth" as it appears to the observer, a view later to be defended by the Gestalt psychologists in terms of the behavioral, as contrasted with the geographical, environmentanother variant of the view that things as they appear are appropriate objects of psychological science.

As professor of psychology at the University of California, E. C. Tolman (18861959) developed an original system of purposive behaviorism that had perhaps much more in common with the psychology of McDougall than it had with the psychology of Watson. Watson was preoccupied with responses to stimuli. Tolman described Watson's behaviorism as molecular, for it was concerned mostly with physiological details; his own he described as molar, for it was concerned with external and integrated behavior and with emergent properties.

Clark L. Hull (18841952), professor at Yale, is known for his inventiveness and originality. His contribution to behaviorism reflects his own interest in methodological studies and the concept of hypothetico-deductive systems. He constructed a miniature system of this type aimed at a rigorous ordering of some of the basic laws of behavior. His deductive dream and his attempt to develop a Galileo-like resolution of behavior into simple externally initiated movements bore a marked similarity to the mechanistic system of Hobbes.

Behaviorism is not strictly an arguable thesis; it is a pronunciamento, a policy statement. The traditional psychologist declares, "I propose to study consciousness by introspection"; the behaviorist says, "I do not; I propose to study behavior by objective methods." The issue is almost as simple as that. There are, however, many arguable issues in particular systems of behaviorism. Reasons can be given for and against policy decisions. There are larger philosophical issues that cannot be evaded.

Roughly three types of behaviorism have emerged: a metaphysical type that says that consciousness does not exist; a methodological type which says that consciousness is not amenable to scientific procedures of investigation; and a radical analytic type, defended chiefly by philosophers, according to which mental facts can all be analyzed in terms of behavior and dispositions to behavior. In Watson's behaviorism and in many others these issues are confused. The behaviorists, no less than Titchener, confused questions of empirical fact with questions of philosophical analysis. It is not possible to know what an emotion is by the introspective observation of emotional states. A prior decision has to be made concerning what to observe, what is to count as an emotion. In the same way it is not possible to know what behavior is by the objective observation of behavior. A prior decision has to be taken about what to observe and about what is to count and what is not to count as an example of behavior. For example, before describing a movement of the body like raising an arm as signaling to a friend or testing the direction of the wind, a person must know what the agent had in mind. This inadequate attention to the question of what constitutes behavior was one of the major weaknesses of behaviorism. Behaviorism is no less riddled by interminable and inconclusive disputes than is introspective psychology. Nevertheless, it has contributed very effectively to the advance of psychology as a biological and an experimental science.

Gestalt psychology

The term Gestalt psychology applies primarily to a school of psychology pioneered by Max Wertheimer (18801943), Kurt Koffka (18861941), and Wolfgang Köhler (b. 1887). Their polemic was directed chiefly against the atomism of traditional psychology and of the established order. They opposed the thesis that perceptual experience is to be explained by a bricks and mortar account of the combining of simple sensations. Their positive thesis was that what is experienced is always organized and consists of wholes which are greater than the sum of their parts. Like all revolutionaries, they exaggerated the difference between their own ideology and traditional doctrine. The fact with which they were concerned had preoccupied philosophers and psychologists from the beginnings of systematic thought. Aristotle's formal cause was a Gestalt concept, and Kant had grappled with the problem in his treatment of the categories; Ward and Stout had grappled with it in their accounts of the development of the perception of space, time, thinghood, and causality, and Mill had seen the problem when he wrote about mental chemistry. Christian von Ehrenfels (18591932), an Austrian philosophical psychologist, introduced the concept of form qualities. There were also contemporary psychologistsfor example, Charles Spearman and Henry J. Wattwho were concerned with the concepts of Gestalt psychology in their own ways.

The outstanding contribution of the Gestalt psychologists was in the number, the variety, and the ingenuity of their experiments. Wertheimer's elegant experiments on the perception of movement were followed by no less elegant experiments by himself, his colleagues, and his disciples on the principles of organization in perceptual experience. In the earlier phases Gestalt psychology was as intellectualist as traditional psychology in its preoccupation with the cognitive experience of the normal adult human mind. Its interest extended, however, to child psychology in the studies by Koffka and to animal psychology in Köhler's studies of insight and learning in apes. Kurt Lewin (18901947) used Gestalt concepts in the study of problems of personality and of human motivation. The Gestalt psychologists were distinguished chiefly by their experimental inquiries, but in their writings there are many pronouncements relevant to the philosophy of mind.

The slogan "The whole is more than the sum of its parts" is a near tautology but a useful tautology. The increasing emphasis placed by Köhler and Lewin on field theory (the theory concerning properties of total fields of activity as contrasted to the properties of isolated units) has also contributed to the philosophy of science in its application to psychology.

The concept of isomorphism (the parallelism between phenomenal experience and neural processes) has given a new slant to the discussion of classical theories concerning the relations of body and mind.

The experimental findings of the Gestalt psychologists have been assimilated into empirical psychology. Its evaluation as a philosophy of nature, life, and mind must take into account not only its historical antecedents but also some less well known but important contemporary theories, such as those, for example, of Spearman and Watt.

Alternatives to Gestalt psychology

Charles Spearman (18631945) made two significant contributions to the development of psychology in the early decades of the twentieth century. The first was through the development of statistical methods in psychology. Building on the studies of Galton and Karl Pearson, he elaborated his two-factor theory for the analysis of human abilities. His second notable contribution was an attempt to formulate principles of cognition, which he believed to be as basic to psychology as Newton's laws had been basic to physics. It was an ambitious plan in which three noegenetic principlesthe apprehension of experience, the eduction of relations, and the eduction of correlateswere set out as necessary and sufficient for the explanation of all the cognitive operations of the human mind. The principles of the eduction of relations had been anticipated by Brown's concept of relative suggestion, but in its detailed elaboration it covered most of the facts of cognitive experience studied by the Gestalt psychologists.

Henry J. Watt (18791925) enters the history of psychology through his experimental studies of judgment and the higher thought process at the Würzburg laboratory. After his return to Britain he spent the rest of his life at the University of Glasgow elaborating a comprehensive theory that was finally presented in his Sensory Basis and Structure of Knowledge (1925). It is a paradoxical fact that atomism, against which Gestalt psychology was directed, should have received its most precise and systematic formulation by a psychologist preoccupied with precisely the facts that Gestalt psychologists were concerned with.

Watt offered an ingenious alternative to Gestalt theory made possible by the sharp distinction he drew between sensationism and associationism, whereas Titchener had treated them as equivalent doctrines. Watt agreed that traditional psychology rested upon two postulates(1) that the elements of mind are sensations and (2) that the compounds are produced by association. He not only accepted the first postulate, but he also refined it with great subtlety. He rejected the second postulate, replacing it with the doctrine that complex cognitive experiences arise through a distinct process of integrationa concept to which he gave a new definition and which he illustrated in great detail. Watt produced an original account of the facts that had previously been interpreted in terms of Mill's mental chemistry, Wundt's creative synthesis, Spearman's noetic principles of eduction, and the principles of Gestalt psychology.

The Gestalt psychologists captured the headlines in the journals of psychology. For a time Spearman had a band of disciples, although Watt's book did not have a second edition. Spearman and Watt had the misfortune of attracting disciples who could neither advance their theory nor excite impassioned critics. Thus, both have been forgotten. Both, however, may be classed among the mute inglorious Miltons of psychology whose works may yet attract the attention of future historians of science.

The philosophy of nature, life, and mind of both Spearman and Watt were, though different from each other, both in the tradition of dualism. That of the Gestalt psychologists was rather differenta dualism of physics and phenomenology. A residual doubt remains. There would appear to be no empirical procedure for deciding between the doctrines of the Gestalt psychologists, of Spearman, and of Watt. The case may again be one in which a choice must be made on grounds of terminological convenience.

Psychoanalysis and derivative schools

The most important revolt against traditional psychology at the turn of the twentieth century was that of Freud and his disciples.

Sigmund Freud created an entirely new psychologypsychoanalysis. This is both a technique of psychotherapy and a body of theory providing a rationale for the technique. The theory developed into an overall account of nature, life, and mind. Freud's philosophy of nature was a conventional nineteenth-century mechanistic materialism predisposing him to an equally conventional preference for physiological explanations of the mind. Thus, it is even more remarkable that his most distinctive and revolutionary doctrines assumed the form of hypotheses to which mechanism and physiology are completely irrelevant.

Central in his system of psychology is the concept of the unconscious. Mind is divided into the conscious, the preconscious, and the unconscious. The conscious is the traditional, familiar, introspectable part of the mindintrospectable thoughts, feelings, and desires. The preconscious consists of all that is out of mind but which can be brought to mind at will or which readily returns to mind in accordance with the accepted laws of association. The unconscious, on the other hand, consists of ideas and wishes, especially wishes, which can be brought into consciousness only by special techniques, of which psychoanalysis is said to be the most fundamental.

Freud's originality did not consist in the discovery of the unconscious, for others before him had hit on this notion, but in postulating that the mind worked in accordance with two different types of lawsthose of the primary processes, which included unconscious processes, and those of the secondary processes of thought. The first were ruled by the pleasure principle, the second by the reality principle. The laws of the primary processes were principles of emotive congruence appropriate to wishes. Freud's great contribution to psychological theory lay in postulating these laws of primary processes to explain such phenomena as hysteria, dreams, parapraxes, and so on which were previously unexplained and among which no one had previously seen any connection.

There are some superficial resemblances between Freud's and Herbart's psychology, but these are only superficial. In Herbart's system the contents of the unconscious were ideas; in Freud's system they were mainly wishes. Herbart was concerned with the movement of ideas between consciousness and Freud's preconscious. He had no clear conception of the unconscious mind in Freud's sense. Herbart's explanation of the movements of ideas were formulated in terms of quasi-mechanical forces, efficient causes, whereas Freud's explanatory principles were, in effect, formulated in terms of a truncated type of teleological concept, the Freudian wish. Similarly, Freud's defense mechanismssublimation, projection, reaction formation, and the likewere quite unmechanical mechanisms. They were goal-directed procedures for protecting the conscious mind against the unwelcome wishes and ideas that had been repressed.

From first to last Freud was concerned with mental conflict, the conflict between opposing motives. At the beginning he emphasized the conflict between primitive instinctive impulses, mainly sexual, and the need to conform to the rules and norms of society. The emphasis later shifted to the conflict between the life and death wishes. At first the world was astounded and shocked by Freud's theories about sex, especially by his account of infantile sexuality. So prominent was sex in his system that a Freudian explanation of any form of behavior came to be generally thought of as an explanation by reference to unconscious sexual desires. His generalized concept of sex was that all pleasure is essentially the pleasure of sexual experience, including the satisfaction of defecation (anal eroticism) and the satisfaction of sucking and feeding (oral eroticism), as well as the satisfaction derived from the genital organs (genital eroticism). This general theory of affective experience makes the thesis of infantile sexuality almost tautological. More significant empirically was the thesis of the universality of the Oedipus complexthe thesis that every male child unconsciously wishes to kill his father and have sexual relations with his mother (female children have an Electra complexthe unconscious wish to replace the mother in her relation to the father). These unconscious desires are obvious sources of the conflicts that issue in neuroses and other forms of aberrant behavior.

In Freud's later writings the emphasis was transferred to the conflict between the life-promoting instincts and the desire for deathEros and Thanatos. When directed outward, the death wish is a source of violence and destruction; when directed inward, it results in suicidal behavior. The concept of the death wish was, however, further generalized. It covered not only the desire to kill and to be destroyed but also the desire to inflict pain and to suffer pain. Thus the odd phenomena of sadism and masochism are explained. As he often did, Freud attempted to reinforce limited hypotheses by highly general theories. The hypothesis of the death wish was based upon the general theory that in all the processes of nature there is a tendency for animated matter to revert to an inorganic state. Slightly less generalized was the theory that all responses to stimuli by an organism were directed to the removal of the stimulus and are thus consummated in unconsciousness, in sleep or death. These speculations were disturbing to his disciples, who felt an obligation to defend them, since these ideas were all but demonstrably mistaken and on the face of it inconsistent with Freud's more basic hedonistic account of human motivation. They were not at all essential to his general theory.

To this phase of Freud's speculations belongs the doctrine that the total personality is organized on three levelsthe id, the ego, and the superego. The id consists of the totality of primitive instinctive impulses, and the ego contains the conscious motives. The concept of the superego is the most interesting and original feature of this hierarchy. Although it was often described as the primitive unconscious conscience, Freud explained it as an introjected image of the parent that continued to issue commands and to administer punishment when those commands were disobeyed. Not a few of Freud's disciples have treated the superego as the source of conscience as traditionally conceived and believe it is the explanation of action that accords with moral principles. This, however, was not Freud's view. He was himself a man of great integrity with very definite ethical principles. These principles were not derived from his own superego but are to be explained in terms of the distinction between the pleasure principle and the reality principle. Action in accordance with the pleasure principle is directed to immediate pleasure regardless of consequences; action in accordance with the reality principle is directed to maximizing pleasure in the long run. This may be little more than a terminological variation on traditional hedonism, but as is often the case, terminological innovation can contribute to enlightenment.

By 1950 Freudian theory was the dominating influence in psychology. Neither the technique of psychoanalysis nor the supporting theory has received scientific validation, but no theory of human motivation and no form of psychotherapy can ignore the theories and practice of Freud. Freud himself protested that psychoanalysis does not attempt to explain everything, but in the human and social sciences there is hardly a question to which Freudian theory is quite irrelevant. The theory of the unconscious has been advanced and the techniques of analysis developed by such distinguished disciples as his daughter Anna Freud, Melanie Klein (a specialist in the analysis of children), and many others in Europe and the United States. Theory and techniques have also been developed by many disciples and eclectics. Two of Freud's disciples who deviated from his theoriesAlfred Adler and Carl Junghave had very considerable influence.

Alfred Adler (18701937) distinguished his system from psychoanalysis by labeling it individual psychology. Before meeting Freud, he had made a special study of the biological phenomena of compensation for defective bodily organs. After his association with Freud he extended his principles to account for all forms of compensation for inferiority, the "inferiority complex." In deviating from Freud, he assigned less importance to unconscious motivation and to sexuality.

Carl Gustav Jung (18751961) labeled his system analytical psychology. He differed from Freud in assigning a less important place to sexual motives and in his account of the unconscious. Jung regarded the libido as an undifferentiated "life force" which became differentiated into a number of instincts or drives. In his long life Jung developed a number of important but highly controversial theories. He elaborated the controversial and obscure concept of the collective unconscious and a theory of archetypal ideas (which has been confused by some with the Platonic concept of archetypes). Less controversial were the results of his experimental studies of word association and his suggestions regarding personality types. His wide-ranging speculations covered alchemy, mythology, and the psychology of religion. Students of religion have found in Jung much of what they found absent or uncongenial in the writings of Freud. The opposition between Freudian and Jungian psychology has provided a modern parallel to the classical distinction between the Aristotelians and the Platonists.

Hormic psychology

In the Wundtian system as interpreted by Titchener the elements of mind were sensations and feelings. Conative experience had been eliminated by reductive analysis. Similarly, the concept of conative behavior had no place in Watsonian behaviorism. The concept of conation was not prominent in early Gestalt theory. Before 1950, however, the concept of conative or goal-directed behavior had been restored as a key concept in most systems of psychology. Tolman, the most sophisticated of the self-proclaimed behaviorists, established a new purposive behaviorism, and Lewin steered Gestalt psychology into the study of volitional processes. Throughout, Freudian theory is permeated by the facts of goal-directedness. The most thoroughgoing exponent of a conative psychology was William McDougall (18711938).

McDougall had a medical education but devoted himself to research in physiology, making several significant discoveries. An important early publication was his brief Physiological Psychology (1905), which contains the germs of his later theories. His most important publication was his Introduction to Social Psychology (1908). This title was unfortunate since the book contains the essentials of his general theory of motivation. Central to this theory was the thesis that there is a limited number of prime movers by whose conative force every train of thought and every bodily activity is initiated and sustained. These prime movers were first described as instincts, but the objections that were raised to his extreme deviation from the traditional biological conception of an instinct led McDougall to redescribe them as propensities.

In his detailed elaboration of these "propensities" McDougall developed an account of instinctive behavior originally suggested by William James. Prior to James instinct had been regarded as a biological mechanism producing rigid and stereotyped forms of behavior that were neither learned nor modified by experience. James drew attention to the cognitive emotional and impulsive components in instinctive action. McDougall developed this idea within the framework of the tripartite analysis of conscious experience that he had learned from Stout. Stressing the extent to which instinctive dispositions are modified both on the cognitive (receptive) side and on the conative (responsive) side, he suggested that the primary instincts are to be defined by reference to the central or affective components, the "primary emotions." He went on to describe the ways in which instinctive dispositions are modified and the ways in which they are organized into more complex motivating dispositions, the sentiments. A sentiment was conceived of as a system of instinctive disposition organized around an idea. Patriotism, for example, is a complex organization of instincts directed to promoting the welfare of a national group. McDougall's account of the structure of human personality was similar to that first set out in the famous sermons of Bishop Butler on human nature (1726). With McDougall, as with Butler, the motivating forces in man are organized in a three-tiered hierarchy. At the base are the primary instincts or propensities. At the second level in Butler's system were certain regulating and controlling principles, such as benevolence and cool self-love, and at the summit was the ultimate controlling principle, which was identified with conscience.

In McDougall's system the basic instincts are organized into and controlled by the sentiments, which function in a similar way to Butler's principles of benevolence and cool self-love. Thus, the parental sentiment is an organization of the maternal instinct together with other instincts, and in McDougall's view it explains all disinterested altruism. The self-regarding sentiment is an organization of the instincts of self-assertion together with others that exercise a similar control over primitive aggressive instincts. It functions in McDougall's theory in a way similar to Butler's cool self-love and Freud's reality principle. At the head of the hierarchy in McDougall's system as the supreme controlling force is a master sentiment that is an elaborated form of the sentiment of self-regard.

Both Butler's and McDougall's accounts of the structure of human personality, of human motivation, and of the basis of volition or self-control have important similarities with, but also important differences from, Freud's hierarchy of id, ego, and superego. Butler's analysis had greater philosophical subtlety than McDougall's, but McDougall's was developed in much greater detail. The central theses were contained in Social Psychology. The details were further elaborated in his later works, such as the Outline of Psychology (1923) and the Outline of Abnormal Psychology (1926). McDougall was himself surprised, as well as gratified, by the outstanding success of his Introduction to Social Psychology. He was to be surprised and disappointed by the reception of what he intended to be his magnum opus, Body and Mind: A History and Defense of Animism (1911). This contained a critical review of the traditional theories of the relations of body and mind in which he eventually decided in favor of interactionism. His general philosophy of nature, life, and mind was that of an orthodox dualist and interactionist. This was later developed into a Leibnizian monadology. The personality of man was conceived as a hierarchy of monads. Every monad is potentially a thinking, striving self, but each differs in degrees of development. At the head of the hierarchy is the supreme monadthe self, which is in command of, and directly or indirectly in communication with, all subordinate monads. The mode of communication was conceived to be telepathic.

McDougall was one of the last of the academic psychologists to attempt a comprehensive system covering all the facts of cognition, feeling, and conation as well as the facts of unconscious motivation. His theories, however, fell out of favor, though not entirely because of specific objections to them. They were outmoded by current trends in both psychology and philosophy. Nevertheless, he exercised a considerable influence on thought and research in motivation theory, not least upon those who differed from him, and he contributed to the reunification of psychology and the biological sciences, which had been separated since Aristotle's day. Indeed, it could be argued that McDougall, like Aristotle, saw that the concept of purpose was both logically irreducible to mechanistic concepts and fundamental for the explanation of human behavior. His mistake was to translate this eminently defensible conceptual doctrine into a genetic doctrine about the origins of behavior. The two do not necessarily go together, for the doctrine that human behavior cannot be explained without recourse to a concept like purpose does not entail the genetic doctrine that men must come into the world equipped with a myriad of built-in purposes.

reaction against reactions

The proliferation of schools continued into the 1930s. Carl Murchison's Psychologies of 1925 was followed by his Psychologies of 1930, and at the time no end to such quinquennial volumes could be foreseen. Psychologists, however, began to tire of these battles among the schools, each of which was in revolt against the established order and at war with the others in revolt. There came a revolt against revolt, a reaction against reactions. Robert S. Woodworth (18691962), who had written the most influential critical commentary on the schools, Contemporary Schools of Psychology (1931), was a leading advocate of a middle-of-the-road psychology. Teaching and practicing psychologists tended to be eclectic; many leaned heavily on one or another of the schools, and only a few remained uncommitted.

Schools were then replaced by "approaches," a term that suggests convergence rather than divergence. Approaches, like viewpoints, are complementary. The new situation favored the emergence of groups of psychologists united in discipleship to a single dominating personality. These groups differed from the schools in that a school was created by several outstanding personalities who, though agreeing on certain basic theses, made individual contributions to the system of psychology defended by the school. There have always been groups of the simpler leader-and-disciples type. Before the age of the schools there were philosophical psychologists with their disciplesfor example, Brentano and Alexius Meinong on the Continent, Ward and Stout in Great Britain, James in the United States. In the schools themselves there were subgroups composed of a man and his disciplesthe Freudians, the Jungians, the Pavlovians, and so on. After the dissolution of the schools new personalities emerged, each with an individual approach or field of specialization; there were psychologists like Piaget at Geneva, Albert Michotte at Louvain, and Tolman and many others in the United States.

relation to philosophy

The history of psychology in the twentieth century is a story of the divorce and remarriage of psychology and philosophy. The trouble began when psychologists claimed the status of empirical scientists. At first the philosophers were the more aggressive, deriding the young science as a bogus discipline. The psychologists hit back and made contemptuous remarks about philosophical logic-chopping and armchair psychology. The arguments were charged with emotion, and neither side emerged with great credit. Slowly, some progress was made toward a diagnosis of the situation, a diagnosis that may well provide the basis for a happy reconciliation.

Psychology has always been, and may well always remain, a parasitic discipline. For twenty centuries it was just a branch of philosophy. To gain emancipation, it entered into willing bondage to the established natural sciences. Increasingly it has claimed to be, and has been increasingly accepted as, a biological science. Aristotle's psychology had a biological orientation, and theories of the temperaments have always had a physiological slant. Since Darwin psychologists have attempted to work down to the biological foundations of mental life, and biologists have extended their field of interest upward to include the more complex functions of organisms traditionally described as mentalperception, learning, problem solving. In the twentieth century psychologists and biologists found a common approach, frame of reference, and interest in such new special studies as ethology, cybernetics, and information theory and a common lack of interest or only a peripheral interest in problems of the philosophy of mind. There have, however, been other developments that have helped to resolve the conflicts between philosophers and psychologists and to clarify the lines of demarcation between work that can properly be done in an armchair and work that must be done on a laboratory stool, in a birdwatcher's blind, or behind a one-way screen.

The behaviorists, in their revolt against Titchener's introspectionism, had taken over quite uncritically Titchener's greatest error. Hegel had attempted to answer questions of empirical fact by a priori reasoning. Titchener made the opposite mistake, supposing that questions of philosophical analysis could be settled by observations made in a laboratory. His mistake is on record; he recalled that in 1888, when first reading James Mill's Analysis of the Human Mind, the conviction flashed upon him, "You can test all this for yourself." He thought he could test it by introspection. The Analysis of James Mill was an exercise in philosophical analysis that can be carried out in a soft armchair, perhaps more efficiently there than on a hard laboratory stool. The behaviorists also fell victim to the same error in confusing introspection and philosophical analysis, in failing to see that questions of analysis arise not only in regard to introspective reports but also in regard to behavioral conceptsstimulus, response, and behavior itself.

However, behaviorists and other biologically minded psychologists were little disposed to either philosophical speculation or philosophical analysis. They were content, like most biologists, to think of the world, regardless of consistency, both in terms of commonsense realism and in terms of the billiard-ball atomism of nineteenth-century physics, thereby following the physicists whenever they revised their theories. Those who had some interest in philosophy followed the prevailing trend in philosophy to some form of phenomenalism.

Reduction of mental concepts

There had been three centuries of philosophical thinking devoted to the elimination of superfluous psychological concepts. At first a mind was thought of as an immaterial substance that, like a material substance, persists through changing states. As a rod of iron passes through states of being hard and soft or black, red, and white in accordance with changes of temperature, so a mind passes through states of joy, sorrow, and so on in accordance with the success and failure of its endeavors. Descartes had described all modes of consciousness as states of the soul, some of which appear to be states of external bodies, others of which appear to be states of the body in which the soul is embodied, and others that really are, as they appear to be, states of the soul itself. In his new way of ideas Locke redescribed experience in terms of the soul, self, or ego being presented with and attending to objects in the mind that chiefly represent things in the external world. Berkeley pointed out, cogently, that there is no way of comparing these representative ideas with the things they are supposed to represent. There were, he suggested, no reasons for, and there were reasons against, supposing that there are material things to be represented. Exit the material world. Then came Hume, who gave an important negative introspective report. He could not observe this soul, self, or ego to which presentations were said to be presented. Exit the soul.

For a long time attempts were made to defend what Titchener described as an act and content psychologythe doctrine that mind consists in mental contents and acts of willing and attending concerned with these contents (without, however, anyone to perform these acts). Late in the nineteenth century Brentano argued that these acts or attitudes are what is distinctive of mind. G. E. Moore based his refutation of idealism on this thesis by distinguishing in sensation the sensing, which alone is distinctively mental, from the sense datum sensed. But, like Hume, he made another negative introspective reportthat the act is diaphanous, unintrospectable. Exit the act, the last claimant to mentality.

This reduction and elimination acquired a temporary finality in Bertrand Russell's neutral monism. Influenced by Moore, Ernst Mach, and William James, he proposed the overall theory that the stuff of which the universe is composed is neutral, not mental or physical. Organized in one way, it issues in the laws of physics; organized in another way, it results in the laws of psychology. Combining these, we have an account of nature. In this long reductive process man first had lost his soul, then his mind, then his consciousness, and finally even his body, which was reduced to a permanent possibility of neutralized sensations.

Linguistic approach

The finality of this form of phenomenalism was short-lived. The conception of philosophy as an inquiry into the ultimate nature of reality was supplanted by the idea that philosophy is the critical analysis of the concepts of science and of common sense. This was in turn replaced by the idea of philosophy as the study of linguistic usages. Instead of asking what mind is, philosophers set out to disentangle the various uses of the word mental, and they became interested in the depth psychologists' uses of new words and of old words in new senses. Philosophers and psychologists began to find a new basis for collaboration. The philosophers clarified concepts; the psychologists attempted to verify by laboratory procedures the hypotheses stated in these concepts.

Not all issues between philosophers and psychologists have been resolved, but there has been notable progress toward a policy of coexistence, and here and there some progress toward cooperation has been made.

See also Animal Mind; Apperception; Behaviorism; Consciousness; Dreams; Emotion; Existential Psychoanalysis; Experience; Gestalt Theory; Guilt; Happiness; Humor; Images; Imagination; Intention; Intuition; Memory; Mind-Body Problem; Pain; Perception; Pleasure; Psychoanalytic Theories, Logical Status of; Religion, Psychological Explanations of; Sound; Thinking; Time, Consciousness of; Touch; Unconscious; Volition.


Boring, E. G. A History of Experimental Psychology. 2nd ed. New York: Appleton-Century-Crofts, 1950.

Boring, E. G. Sensation and Perception in the History of Experimental Psychology. New York: Appleton-Century, 1942.

Boring, E. G. et al. History, Psychology, and Science: Selected Papers. New York: Wiley, 1963.

Flügel, J. C. A Hundred Years of Psychology, 18331963. London: Macmillan, 1933. Enl. ed., New York: Basic, 1964. The enlarged edition has an additional part, by Donald J. West, on the period from 1933 to 1963.

Hamlyn, D. W. Sensation and Perception. London: Routledge and K. Paul, 1961.

Hearnshaw, L. S. Short History of British Psychology, 18401940. New York: Barnes and Noble, 1964.

Murphy, Gardner. Historical Introduction to Modern Psychology. Rev. ed. New York: Harcourt Brace, 1949.

Peters, R. S., ed. Brett's History of Psychology. Rev. ed. London and New York, 1962. Consult pp. 769772 for a bibliography of all major texts in the history of psychology. This work is an abridgment and updating of G. S. Brett's three-volume History of Psychology (London: Allen, 1912) and is the only complete history of psychology.

R. S. Peters (1967)

C. A. Mace (1967)

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