Kant, Immanuel

(b. Königsberg, Germany [now Kaliningrad, R.S.F.S.R.], 22 April 1724; d. Königsberg, 12 February 1804)

philosophy of science.

Kant was the fourth child of Johann Georg Cant and Anna Regina (Reuter) Cant. His paternal grandfather was an immigrant from Scotland, where the name Cant is still not uncommon in the northern parts. Immanuel changed the spelling to Kant in order that the name might conform more comfortably with the usual pratices of German pronunciation. His father was a saddle maker of modest means. His mother was much given to Pietism, a Protestant sect (not unlike the Quakers and early Methodists) which flourished in northern Germany at the time.

When Kant was ten, he entered the Collegium Fridericianum, intending to study theology. But he actually spent more time with classics, and he became quite adept in Latin. In 1740 he entered the University of Königsberg and studied mainly mathematics and physics with Martin Knutzen and Johann Teske. These years doubtless influenced him much in his interest in the philosophy of science. In 1746 Kant’s father died, and he was forced to interrupt his studies to help care for his brother and three sisters by being a private tutor in three different families successively for a period of some nine years. Finally, in 1755 he was able to resume his studies at the university and received his doctorate in philosophy in the autumn of that year. For the next fifteen years he earned a meager living as a Privatdozent lecturing on physics and nearly all aspects of philosophy. In 1770 he was given the chair of logic and metaphysics at the University of Königsberg, a position which he held until he retired in 1797.

Although Kant was brought up in Pietistic surroundings and in his youth even considered becoming a minister, in his maturity he became the one who, above all others, liberated philosophy and science from theology. His single-minded devotion to both philosophy and science also accounts largely for the fact that he never married. He was slightly built and gave the appearance of having a delicate constitution, but his careful attention to the laws of health and the regularity of his habits enabled him to live to be almost eighty.

Kant was very modest in his style of living. In 1783 he purchased a house in the center of town and quite regularly thereafter entertained friends at dinner. The number of his table companions was never large because his dinner service could accommodate but six persons. These companions were for the most part men of great culture and learning, and his dinners were widely known for the liveliness and diversity of the conversation.

The German writer Johann Gottfried von Herder said that Kant in his prime had the happy sprightliness of a boy and that he continued to have much of it even as an old man. He had a broad forehead, Herder continued, that was built for thinking and that was the seat of an imperturbable cheerfulness and joy. Speech rich in thought issued from his lips. He also possessed playfulness, wit, and humor. He enlivened his lectures and conversations by drawing on the history of men and peoples and on natural history, science, mathematics, and his own observations. He was indifferent to nothing that was worth knowing, concluded Herder.

Even though Kant is widely considered to be one of the two or three greatest philosophers that Western civilization has produced, he was also much interested in science and especially in the philosophy of science. He was not an experimental scientist and did not contribute to the body of scientific knowledge, but he was much concerned with the foundations of science and made significant contributions to that field. He has sometimes been accused (as by Erich Adickes in his Kant als Naturforscher) of being an armchair scientist. He might more accurately be called an armchair philosopher speculating on the fundamental bases of science. He was not interested in gleaning facts and data; rather, he speculated concerning the grand scheme in which the facts gleaned by others are arrayed.

The two main influences on Kant in his philosophical reflections on science were Leibniz and Newton. During his first period of study at the University of Königsberg, from 1740 to 1746, Knutzen taught that version of Leibniz’s metaphysics which the German philosopher Christian von Wolff had made popular. He also taught the mathematical physics which Newton had developed. He revealed to the young Kant the various oppositions, puzzles, and contradictions of these two great natural philosophers.

The nature of space and time was what interested the young Kant most in these disputes between Leibniz and Newton. He studied the famous exchange of letters between Leibniz and Samuel Clarke, a defender of Newton’s philosophy. Leibniz claimed that the universe is made up of an infinitude of monads, which are simple, immaterial (spiritual) substances. Every monad is endowed with some degree of consciousness. He conceived of space as a set of relations which the monads have to one another; it is the order of coexistent things. He thought of time as the relations of the successive states of consciousness of a single monad. Physical bodies, on this theory, are groups of monads. Mathematically considered, every monad is a dimensionless point. Length, breadth, and position can be represented as relations of monads. Space, then, is a continuous, three-dimensional system of mathematical points corresponding to the order of a plenum of distinct monads. Time has but one dimension; succession and coexistence are the only temporal relations, corresponding, as they do, to the order of perceptions in the consciousness of a monad. For Leibniz, then, space and time were relations among things (monades) which would have no existence whatever if there were no monads.

By contrast, Newton held that space and time are infinite and independent of the physical bodies that exist in space and time. For him space and time were things, and they would exist even if there were no bodies. He held that are absolute positions in space and time that are independent of the material entities occupying them and, furthermore, that empty space (void) and empty time are possible. Leibniz denied both tenets. Neither Leibniz nor Clarke was able fully to undermine the position of the other, and the result was an impasse.

In his early years Kant pondered the nature of space and time first from the point of view of Leibniz and then of Newton, but eventually he found both positions unsatisfactory. In his Thoughts on the True Estimation of Living Forces (1747) he took Leibniz’s view and tried to explain the nature of space by means of the forces of unextended substances (monades) that cause such substances to interact. He attempted to account for the threefold dimensionality of space by appealing to the laws that govern such interactions; but he was not very successful, as he himself admitted.

In his On the First Ground of the Distinction of Regions in Space (1768) Kant took Newton’s view that space is absolute and argued against Leibniz’s relational theory of space. He used the example of a pair of human hands. They are perfect counterparts of one another, yet they are incongruent (like left-and right-hand spirals). The two hands are identical as far as their spatial relations are concerned, but they are, nevertheless, spatially different. Therefore space is not just the relationship of the parts of the world to one another.

When Kant was inaugurated as professor of logic and metaphysics in 1770, he submitted a dissertation, in accordance with the custom of the time. It was entitled On the Form and Principles of the Sensible and Intelligible World. Here his views on space and time had developed to a point that was very close to the views enunciated in the Critique of Pure Reason (1781). Space and time are the schemata and conditions of all human knowledge based on sensible intuition. Our concepts of space and time are acquired from the action of the mind in coordinating its sensa according to unchanging laws. The sensa are produced in the mind by the presence of some physical object or objects. Space and time are now based epistemologically on the nature of the mind rather than ontologically on the nature of things, either as a relation among monads (Leibniz) or as a thing (Newton’s absolute space). Kant had turned from modes of being to ways of knowing. This new epistemological view of space and time provided him with a way of reconciling the opposed views of Leibiz and Newton. Space and time are indeed the relational orders of contemporaneous objects and successive states, inasmuch as space and time are the conditions of intuitive representations of objects, rather than being mere relations of independent substances (monads). Space and time are indeed absolute wholes in which physical objects are located, inasmuch as they are forms of sensible intuition lying ready in the mind, rather than being independently existing containers for physical objects.

Kant’s in the Critique differ from those of the Dissertation in that space and time are held in the former to be passive forms of intuition by means of which a manifold of sensa are presented to the understanding, which has the active function of synthesizing this manifold. Space is the form of all appearances of the external senses, just as time is the form of all appearances of the internal sense. As such, space and time are nothing but properties of the human mind. Everything in our knowledge that belongs to spatial intuition (extension), change according to which change of location is determined. The representations of the external senses are set in time, which contains nothing but relations of succession, coexistence, and duration.

Geometry is based on the pure intuition of space. To say that a straight line is the shortest distance between two points involves an appeal to spatial intuition. The concept of straight is merely qualitative. The concept of shortest is not already contained in the concept of straight but is an addition to straight through recourse to the pure intuition of space. Accordingly, the propositions of geometry are not analytic but a priori synthetic. So are the propositions of arithmetic. The concept of units in the pure intuition of time. Leibniz had claimed that the propositions of mathematics are analytic. For Kant even some of the propositions of mechanics cannot attain its concepts of motion without employing the representation of time.

As we have seen, Kant rejected Newton’s absolute space conceived as an independently existing whole containing all physical objects. In the Metaphysical Foundations of Natural Science (1786) he pointed out a meaning for “absolute space” which makes it a legitimate idea. At the beginning of “Phoronomy” in that treatise, he distinguishes relative space from absolute space. Relative (or material or empirical) space is the sum total of all objects of experience (bodies). Such space is movable because it is defined by material entities (bodies). If the motion of a movable space is to be perceived, that space must be contained in another, larger space in which it is to move. This larger space must be contained in another, still larger one, and so on to infinity. Absolute space is merely that largest space which includes all relative ones and in which the relative ones move. As such, absolute (empty) space cannot be perceived because it is not defined by material entities, as relative (empirical) spaces are, and so exists merely in idea, with no actual ontological status. Kant claimed that Newton mistakenly endowed such absolute space with ontological significance.

The terms “physical entities,” “material objects,” “bodies,” and similar ones have been used from time to time in the foregoing discussion without any exact definitions being given for them. They are all roughly analogous terms and involve what Kant usually calls “matter” or “body.” Toward the end of the “Dynamics” in the Metaphysical Foundations of Natural Science he does say that a body is matter between determinate boundaries and thus has definite shape. “Matter” is therefore a more general term than “body,” but he often uses the two interchangeably. What, indeed, is matter for Kant? In the development of his thought at the stage of the Dissertation, he distinguished a sensible world from an intelligible one. The former is the world which sense reveals, and the latter is what the intellect reveals. He called the former world phenomenal and the latter noumenal. The former is the world of things as they appear, while the latter consists in things as they are. Sensibility with its two pure forms, space and time, provides the foundation for the validity of physics and geometry; however, the scope of the application of these two sciences is restricted to phenomena. Intellect with its pure concepts of substance, cause, possibility, existence, and necessity provides the foundation for the validity of the metaphysics of monads; this science yields an intellectual knowledge of such substances (monads) as they are in themselves, but there is no sensible knowledge of monads. The concepts of matter and body are empirical, sensitive ones belonging to physics but not to metaphysics.

By the time Kant’s thought attained full maturity in the Critique of Pure Reason, the pure concepts of substance, cause, possibility, existence, and necessity had become coterminous with the two pure forms of intuition, space and time, in having a valid application to nothing but phenomena. The intelligible world of monads, conceived in the Dissertation as a known realm of things-in-themselves, becomes in the Critique unknowable realm of noumena underlying the knowable realm of Phenomena. One has a detailed and actual knowledge of matter and body but only a problematic knowledge of monads and noumena. The noumena did not wither away completly in the idealist like Berkeley or a phenomenalist like Hume. Rather, Kant was a type of realist not unlike Descartes or Locke in his claim that appearances are not all that there is but are all that one has an actual and detailed knowledge of. There is a reality behind the appearance, but one has only a problematic concept of this reality. He often characterized this position of the Critique as transcendental idealism in order to distinguish this brand of idealism from the extreme form typified by Berkeley.

And so matter can be defined, in most general terms, as an appearance given in space. When one turns to a more particular characterization of matter, one finds that Kant”s mature theory of matter developed as an opposition to the atomist view of matter held by Newton and the monadist view of matter held by Leibniz. For Newton matter is composed of physical espouse some form of simple realism and doubtless would have held that these atoms would move about in empty space even if there were no sentient beings anywhere to perceive them. The atoms are absolutely impenetrable, and this means that the matter contituting an atom coheres with a force that cannot be overcome by any existing force in nature. Atoms are absolutely homogeneous as to density. They differ from one another only in size and shape. Bodies are aggregates of such atoms and differ in density according to how much empty space, or void, is interspersed among the atoms.

In the “Dynamics” of the Metaphysical Foundations Kant objected to such absolute impenetrability as being an occult quality that no experiment or experience whatsoever could substantiate. We have seen earlier what Kant thought about absolute, empty space. Newton thus regarded matter as an interuptum. So also did Kant in his early work entitled Physical Monadology (1756). But in the Critical thought of the Metaphysical Foundations, he rejected all forms of atomism and monadology. He maintained that matter is a continuum, as we shall see.

Motive forces were for him the fundamental attributes of matter, a position which he held even in the days of the Physical Monadology. By contrast, Newton had taken a different view on the relation between forces and matter. For him atoms are inert but mobile. Since inertia is an entirely passive property of the atoms, they must be moved by an active principle external to them. God is the ultimate cause of gravitational motion by virtue of His acting through the immaterial medium of absolute space, as one can infer from various scholia in the Principlia and queries in the Opticks. Accordingly, Newton did not regard attraction (as Kant did) as a basic property of matter itself. For Kant only two kinds of moving forces are possible: repulsive and attractive. If two bodies (regarded as mathematical points) are being considered, then any motion which the one body can impress on the other must be imparted in the straight line joining the two points. They either recede from one another or approach one another; there are no other possibilities. Since forces are what cause bodies to move, the only kinds of forces are therefore repulsive and attractive.

When one body tries to enter the space occupied by another body, the latter resists the intrusion and the former is moved in the opposite direction. The repulsive (or expansive) force exerted here is also called elastic. For Kant all matter is originally elastic, infinitely compressible but impenetrable—one body cannot compress another to the extent that the first occupies all the space of the second. He called such elasticity. “relative impenetrability” and contrasted it with the absolute impenetrability posited by atomism. The relative kind has a degree that can be ascertained by experience—for instance, gold is more penetrable than iron—whereas the absolute kind is open to no experience whatsoever. On the atomic theory, bodies are compressed when the empty space among the atoms constituting bodies is eliminated and the atoms stand tightly packed. But once so packed, they admit of no further compression.

Unless there were another force acting in an opposite direction to repulsion, that is, acting for approach, matter would disperse itself to infinity. By means of universal attraction all matter acts directly on all other matter and so acts at all distances. This force is usually called gravitation, and the endeavor of a body to move in the direction of the greater gravitation is called its weight. If matter possessed only gravitational force, it would all coalesce in a point. The very possibility of matter as an entity filling space in a determinate degree depends on a balance between repulsion and attraction. Sensation makes us aware of repulsion when we feel or see some physical object and ascertain its size, shape, and location. Repulsion is directly attributed to matter. Attraction is attributed to matter by inference, since gravitation alone makes us aware of no object of determinate size and shape but reveals only the endeavor of our body to approach the center of the attracting body.

True attraction is action at a distance. The earth attracts the moon through space that may be regarded as wholly empty. And so gravity acts directly in a place where it is not. Descartes and others thought this to be a contradictory notion and tried to reduce all attraction to repulsive force in contact. Attraction is therefore nothing but apparent attraction at a distance. Descartes propounded the theory of a plenum with fourteen vortices to account for the celestial motions of the planets about the sun and the moons about the planets. Newton objected to such plenum and vortices because he thought that the friction between the celestial bodies and this hypothesized swirling fluid medium would slow down the celestial motions and eventually terminate them. He, like Kant, espoused a true attraction rather than an apparent one.

If Kant had ever critically examined Newton’s suggestions as to the ultimate cause of gravitation, he doubtless would have had emphatic objections. He showed in the Critique of Pure Reason that God’s existence cannot be established by theoretic reason. For him attraction is a property of matter itself. He argued against Descartes’s apparent attraction by pointing out that such attraction operates by means of the repulsive forces of pressure and impact so as to produce the endeavor to approach, just as in the case when one billiard ball approaches another after the first has been hit by a cue. But there would not even be any impact or pressure unless matter cohered in such a way as to make such impact and pressure possible. Matter would disperse itself to infinity if it possessed nothing but repulsive force. Hence there must be a true attraction acting contrary to repulsion in order for impact and pressure to bring about even apparent attraction.

Thus matter in general was reduced by Kant to the moving forces of repulsion and attraction. He appealed to these forces to account for the specific varieties of matter. Attraction depends on the mass of the matter in a given space and is constant. Repulsion depends on the degree to which the given space is filled; this degree can vary widely. For example, the attraction of a given quantity of air in a given volume depends on its mass and is constant, while its elasticity is directly proportional to its temperature and varies accordingly. This means that repulsion can, with regard to one and the same attractive force, be originally different in degree in different matters. Consequently, a spectrum of different kinds of matter each having the same mass (and therefore having the same attraction) can vary widely in repulsion—running, for instance, from the density of osmium to the rarity of the ether. And so every space can be thought of as full and yet as filled in varying measure.

Kant claimed that matter is continuous quantity involving a proportion between the two fundamental forces of attraction and repulsion. For an atomist like Newton matter is discrete quantity, and the force of attraction in his theory is superadded through the agency of God. The varying densities of elements and compounds of matter are for Newton a function of the amount of empty space interspersed among the atoms. Empty space, according to Kant, is a fiction that can be discerned by no sense experience whatever. The senses reveal to us only full spaces. Kant’s theory of matter committed him to accept the existence of an ether.

The ether was mentioned in many of his writings. In his doctoral dissertation, entitled A Brief Account of Some Reflections on Fire (1755), Kant said in proposition VIII that the matter of heat (or the caloric) is nothing but the ether (or the matter of light) which is compressed within the interstices of bodies by means of their strong attraction. In the Metaphysical Foundations of Natural Science he accepted the existence of the ether cautiously, as a hypothesis that he found more plausible than the atomists’ hypothesis of the reality of absolutely impenetrable atoms and absolutely empty space. Toward the end of chapter 2 the ether is characterized as a matter that entirely fills space, leaving no void. It is so rarefied that it fills its space with far less quantity of matter than any of the bodies known to us fill their spaces. In relation to its attractive force the repulsive force of the ether must be incomparably greater than in any other kind of matter known to us.

Between 1790 and 1803 Kant worked on what is now called the Opus postumum. At his death this unfinished work survived as a stack of handwritten pages, which were eventually gathered by editors into thirteen fascicles (Convoluten). Sections of it constitute coherent wholes, others provide illustrations, and still others are repetitions of earlier works. The Opus appears in Volumes XXI and XXII of the Royal Prussian Academy edition of Kant’s works. Part of the Opus contains the Transition From the Metaphysical Foundations of Natural Science to Physics. The theory of the ether figures in almost all parts of the Transition but especially in Convolute X, XI, and XII of the Opus. There the ether is characterized as a matter that occupies absolutely every part of space, that penetrates the entire material domain, that is identical in all its parts, and that is endowed with a spontaneous and perpetual motion.

Kant based his proof of the ether’s existence upon the unity of experience. Space, which is unitary, is the form of all experience; hence experience is unitary. Experience is a system made up of a manifold of sense perceptions synthesized in space by the intellect. These perceptions are caused by the actions of the material forces which fill space. Accordingly, the motive forces of matter must collectively be capable of constituting a system in order to conform to the unity of possible experience. Such a system is possible only if one admits, as the basis of these forces, the existence of an ether that has the properties listed above. Therefore, the existence of the ether is the a priori condition of the system of experience. Many critics have found this proof unconvincing, as well they might. The Transition, as it has come down to us, is merely a series of sketches for a work that was never finished. Accordingly, it suggests about as many unanswered questions as it provides solutions.

Kant in his mature period opposed not only atomism but also all forms of monadology. He was like Leibniz and unlike Newton in that he put the emphasis, both in his youth and in his maturity, on force rather than on atomic particles of impenetrable mass. In the Physical Monadology (1756) he even claimed (following Leibniz) that bodies are composed of monads, which are indivisible, simple substances. The space which bodies fill is infinitely divisible and is not composed of original, simple parts because space does not have any substantiality; it is only the appearance of the external relations bound up with the unity of the monad. So conceived, the infinite divisibility of space is not opposed to the simplicity of monads. Matter is not infinitely divisible, while space is. But by the time his thought had arrived at the critical phase represented by the Critique of Pure Reason and the Metaphysical Foundations, Kant had repudiated both the view (derived from Leibniz) that bodies are composed of monads and the view (espoused by Leibniz) that space is a relation among monads. Perceptible matter was now continuous quantity, and space was a form of sensible intuition. What did he think now about the infinite divisibility of matter and space? One must turn to the Second Antinomy in the “Dialectic” of the Critique and the “Dynamics” of the Metaphysical Foundations to learn the answer.

The outcome of these discussions is this: Matter as appearance is infinitely divisible and therefore consists of infinitely many parts, but matter as appearance does not consist of the simple (either atoms or monads); matter as thing-in-itself does not consist of infinitely many parts (either atoms or monads), but matter as thing-in-itself does consist of the simple. It was pointed out earlier that according to Kant’s position of transcendental idealism, we have actual cognition of things as appearances and a problematic concept of the reality behind the appearance. Accordingly, matter can be regarded as appearance or as the reality (thing-in-itself) behind the appearances.

Intuitive space is divisible to infinity. Any matter filling such space is also divisible to infinity. But this means that matter as appearance is infinity. But this means that matter as appearance is infinitely divisible; it does not mean that matter as thing-in-itself consists of infinitely many parts (as an atomist or a monadist might claim). Only the division of the appearance can be infinitely continued, not the division of the thing-in-itself. Any whole as thing-in-itself must already contain all the parts into which it can be divided. But the division process can never be finished. And so the thought that matter as thing-in-itself contains infinitely many parts is self-contradictory.

Furthermore, it cannot be maintained that matter as appearance is made up of the simple. The composite of things-in-themselves must consist of the simple, since the parts must be given before all composition. But the composite in the appearance does not consist of the simple, because an appearance can never be given in any way other than as composite (extended in space); its parts can be given only through the process of division, and therefore not before the composite but only in it (and thus the atomist and monadist are foiled again).

Even though matter as appearance is mathematically divisible into infinitely many parts, no real distance of parts is to be assumed. Physicists usually represent the repulsive forces of the parts of elastic matters (for instance, a gas) when these matters are in a state of greater or lesser compression as increasing or decreasing in a certain proportion to the distance of their parts from one another. This is necessary for the mathematical construction of the concept corresponding to such a state of elastic matters; in this construction all contact of parts is represented as an infinitely small distance. The Posited spatial distance of the parts should be understood, however, as nothing but a mathematical convenience, necessary convenience though it is. In reality, matter is continuous quantity, and there is no spatial distance between its parts; they are always in contact.

Time, space, matter, force—Kant’s views on these fundamental concepts of natural science have now been examined; but motion has not yet been considered in any detail. In contrast with Newton, Kant claimed in the “Phenomenology” of the Metaphysical Foundations, as well as in the earlier New Conception of Motion and Rest (1758), that all motion is relative. The motion of a body is the change of its external relations to a given space. If a ball rolls on a table top, it changes its position relative to various points on the top. But we have the same change of positions if the ball remains at rest and the table moves under it in the opposite direction with the same velocity. Hence the rectilinear motion of a body with regard to an empirical space can be viewed as either the body moving by reference to the space at rest or as thebody at rest and the space moving relative to it. It is impossible to think of a body in rectilinear motion relative to no material space outside of it. Matter can be thought of as moved or at rest only in relation to matter and never by reference to mere space without matter. Furthermore, there is no fixed empirical point by reference to which absolute motion and absolute rest can be determined. The center of the sun might be fixed as the center of our solar system, but our solar system moves relative to other solar systems in the Milky Way, and the Milky Way moves relative to other galaxies, and so on.

Accordingly, there is no empirical space defined by matter that can provide a reference system for all possible rectilinear motions of bodies in the universe. Therefore, all motion or rest is merely relative, and neither is absolute. But the empirical space (for instance, the table top) in relation to which a body (for instance, the ball) moves or remains at rest must itself be referred to another (absolute) space at rest within which this given empirical space is movable. If one did not invoke such immovable, absolute space, one would be claiming that the given empirical space isimmovable and hence absolute; but by experience all material spaces are movable. This ultimate absolute space by reference to which all empirical spaces are movable (and hence relative) exists merely in thought and not in fact, since only empirical (material) spaces actually exist. But such absolute (immovable, immaterial) space is nevertheless a necessary idea that serves as a rule for considering all motion therein as relative. Everything empirical is movable in such ideal absolute space; and all such motions in it are valid as merely relative to one another, while none is valid as absolute. And so the rectilinear motion of a body in relative space is reduced to absolute space when one thinks of the body as in itself at rest but thinks of the relative space as moved in the opposite direction in absolute space.

The circular motion of a body might seem, at first glance, to be an absolute motion. In contrast with the foregoing case of rectilinear motion, it is not all the same whether the earth is regarded as rotating on its axis while the heavens remain still (Copernicus) or the earth is regarded as staying still while the heavens rotate about it (Ptolemy). Both give the same appearance of motion. But the former case is the true one, while the second one is false. To prove that the earth rotates, Kant says that if one puts a stone at some distance from the surface of the earth and drops it, then the stone will not remain over the same point of the earth’s surface in its fall but will wander from west to east. Accordingly, the rotation of the earth on its axis (or the rotation of any other body) is not to be represented as externally relative. But does this mean that the motion is absolute? Even though circular motion exhibits no real change of place with regard to the space outside of the rotating body, such motion does exhibit a continuous dynamic change of the relation of matter within its space. If the earth were to stop spinning, it would contract in size. The present size of the earth involves a balance between centrifugal forces and attracting ones. Hence the actuality of the earth’s rotation rests upon the tendency of the parts of the earth on opposite sides of the axis of rotation to recede from one another. The rotation is actual in absolute space, since this rotation is referred to the space within, and not to that outside of, the rotating body. And so rotation is not absolute motion but is a continuous change of the relations of matters (or parts of the rotating body) to one another; this change is represented in absolute space (the space within the rotating body), and for this reason such change is actually only relative motion.

The case of the translation of body relative to a material reference system and the case of a rotating body have now been considered. What about the third and last case, in which one body hits another? Is this motion absolute? In this case both the matter and the (relative) space must necessarily be represented as moved at the same time: in every motion of a body whereby it is moving with regard to another body, an opposite and equal motion of the other body is necessary. One body cannot by its motion impart motion to another body that is absolutely at rest; this second body must be moved (together with its relative space) in the opposite direction with just that quantity of motion which is equal to that quantity of motion which it is to receive through the agency of the first body and in the direction of this first one. Both bodies, subsequently, put themselves relative to one another—that is, in the absolute space lying between their two centers—in a state of rest. But with reference to the relative space outside of the impacting bodies, the bodies move after impact with equal velocity in the direction in which the first body is moving. This same law holds if the impact involves a second body that is not at rest but moving. There is no absolute motion in this third case, even though a body in absolute space is thought of as moved with regard to another body. The motion in this case is relative not to the space surrounding the bodies but only to the space between them. When this latter space is regarded as absolute, it alone determines their external relation to one another. And so this motion is merely relative.

In the case of rectilinear motion, the change of place may be attributed either to the matter (that is, space at rest and matter moving with respect to it) or to the space (that is, matter at rest and space moving with respect to it). In the case of rotatory motion, the change of place must be attributed to the matter. In the case of colliding bodies, both the matter and the (relative) space must necessarily be represented as moved at the same time. Motion is relative in all three cases by reference to absolute space: in the first case by reference to absolute space outside of the body, in the second to absolute space inside of the body, and in the third to absolute space between two bodies.

In a pre-Critical work entitled Universal Natural History and Theory of the Heavens (1755) Kant was much more favorably disposed toward Newton than he was in his mature period. In fact, the full title of the work has this addition: An Essay on the Constitution and Mechanical Origin of the Whole Universe Treated According to Newtonian Principles. In this book Kant went far beyond anything that is to be found in Newton’s own writings. Newton aimed at nothing more than describing and explaining the regularities that exist in the world in its present state of evolution. He paid special attention to the regularities of the planets and their motions around the sun, but nowhere did he try to explain, on the basis of his own mechanical principles, how the solar system originated and reached its present state of uniformity. In his Theory of the Heavens, Kant, by a series of bold strokes, anticipated astronomical facts that were later confirmed by very powerful observational techniques and with the help of relativistic cosmological theory. He conjectured that our solar system is a part of a vast system of stars making up a single galaxy, that the so-called nebulous stars are galactic systems external to but similar to our own galaxy (a fact that was not confirmed until the twentieth century), and that there are many such galaxies making up the universe as a whole. Much of this thought was stimulated by the work of an Englishman, Thomas Wright of Durham, entitled Original Theory or New Hypothesis of the Universe (1750).Kant read an abstract of this book in a Hamburg newspaper of January 1751. Wright gave the first essentially correct interpretation of the Milky Way and suggested that the nebulae are systems of stars much like our own galaxy. Newton provided Kant with the fundamental physical principles to help him in the development of his cosmogony, while Wright gave suggestions for working out the particulars of the spatial organization of the main components of the universe as a whole.

At this pre-Critical stage Kant claimed that the world had a beginning in time and is infinite in spatial extent. The universe came into existence through an act of creation on the part of a transcendent deity. In the Critique of Pure Reason these claims were presented as unresolvable antinomies. In the First Antinomy the thesis claims that the world has a beginning in time and is also limited spatially, while the antithesis claims that the world has no beginning and is not limited spatially. In the Fourth Antinomy the thesis claims that an absolutely necessary being belongs to the world as its part or as its cause, while the antithesis claims that no absolutely necessary being exists anywhere in the world, nor does such a being exist outside the world as its cause. However, in his Universal Natural History and Theory of theHeavens, Kant adopted the theistic view (espoused also by Newton and Leibniz) that the cosmos as a whole owes its genesis to a Mosaic deity.

But once God had created time, space, and matter and had endowed them with the very laws that Newton eventually discovered, how did the universe evolve? The term “natural history” in the title of the work indicates that Kant was interested in an evolutionary account of the universe. On this subject he made suggestions that resemble those later set forth by Laplace. Kant claimed that the planets of our solar system arose ffom the condensation of primordial diffused matter. This position contrasts with one claiming that some celestial body passed near our sun and set up cataclysmic actions that caused the planets to be born of our sun through the agency of tidal forces. For Kant the sun, the planets, and their moons all originated by a process of condensation of a diffused mass of widely distributed, thin matter (or, in other words, a nebulous mass of matter). He appealed to the Newtonian attraction and repulsion of the various material particles of the original nebulous mass as being the causes of the solar system’s flattening out into a disk. Other astronomical systems in the universe developed in a similar way.

On Kant’s view the universe is not a static mechanism; it undergoes a fundamental change. Various regions of the universe undergo cyclical changes, being born as just described and dying when the train of planets associated with each star tends to run down and eventually falls back into its respective sun. The sun then heats up with this new matter and eventually explodes into a nebular cloud of matter. Our own developed world is midway between the ruins of the nature that has been destroyed and the chaos of the nature that is still unformed. He claimed that this Phoenix of Nature burns itself only in order to revive from its ashes in restored youth through all the infinity of times and places.

Cosmological theory has made great advances since Kant’s day, but his theory has nonetheless inspired proponents of recent theories. C. F. von Weizsäcker, in his History of Nature (1949) and again in his Gifford lectures for 1959–1960 (entitled The Relevance of Science), has espoused the view that the planets of our solar system were formed from a nebula that surrounded the sun. G. Kuiper of Yerkes Observatory thinks that some denser parts of the nebula condensed further under the influence of their own gravity—the very view that Kant advanced. Kant has also been the object of much criticism. The claim has been made by many that he put forth bold conjectures before the experimental evidence was in and that he even twisted some evidence that was in so that it would conform with his theories. Perhaps he did make too many bold conjectures; but if such conjectures were never made, would science ever make much progress? In his Theory of the Heavens, Kant borrowed the principles of Newton’s system of the world and by a sort of thought experiment used them to extend and deepen man’s picture of the universe. It is a wonder that his though experiment turned out to be so close to much of subsequent cosmological theory.

In the middle of the preface to the Theory of the Heavens, Kant said that it would be possible to grasp the origin of the whole present constitution of the universe by means of mechanical (efficient) causes before it would be possible to grasp the production of even a single herb or a caterpillar by means of mechanical causes alone. He did not categorically deny the possibility that organisms might some day be completely explained mechanically. But in the Critique of Teleological Judgment (1790), Kant did deny the possibility of such an explanation. All the phenomena of inanimate nature can be explained in terms of the motion of matter in space and enduring through time, while for living things such efficient causes are not enough—they must be explained in terms of an end and thus require final causes in addition to efficient ones. In more modern terms, biology, for Kant, cannot in the final analysis be explained solely in terms of physics and chemistry.

Kant was opposed to the Cartesian conception of animal machines; no one can or ever will be able to produce a caterpillar from a given bit of matter. An organism exists as a physical end and is both cause and effect of itself. The parts of an organism, both in their existence and in their from, are possible only by their relation to the whole; furthermore, the parts combine spontaneously to constitute the unity of a whole by being reciprocally cause and effect of their form. A machine has only motive power, while an organized being possesses inherent formative power, which it imparts to raw materials devoid of form.

An oak tree, for example, prepares the matter that it assimilates; and it bestows upon this matter a specifically distinctive quality which mere mechanical nature cannot supply. The tree develops itself by means of a material which the tree itself produces through an original capacity to select and construct the raw material that it derives from nature outside of it. It is as though the tree were itself a supremely ingenious artisan in the building of itself, and the subjunctive mood must be emphasized here. One cannot claim that there really is an end in the thing that is operating in its production; to do so would be to foist an unprovable anthropomorphism on organisms. A person coughs when some water goes down his windpipe while he is taking a drink. Substances heavier than air trigger the coughing mechanism. Such a mechanism is said to have adaptive significance for the organism, in that it enables the organism to live. But it cannot be said that the cough mechanism is intended to keep the organism alive, except on an analogy with artistic production. Final causes are merely regulative concepts which human beings use to comprehend biological organisms, which differ essentially from inorganic entities. One deals with them by means of an analogy with artifacts; it is as though a tree organized itself in a way not unlike the way an artisan forms his product.

Finality is read into the facts, and teleological principles are nothing but heuristic maxims whose justification resides in their fruitfulness in providing systematic comprehension of living organisms. When finality is so viewed, the question of whether, in the unknown inner basis of nature itself, efficient causes and final ones may cohere in a single principle is left open. Accordingly, teleology and mechanism in no way contradict one another, as Kant explains with the greatest epistemological subtlety in §77 of the Critique of Teleological Judgment. Efficient causes are concepts that determine (and do not merely regulate) our knowledge of phenomena. Therefore, the investigations of biology must be pushed as far as possible in the direction of efficient causes; the simple mechanism of nature must be the basis of research in all investigation of biological phenomena. But this does not mean that such phenomena are possible as entities solely on the basis of efficient causation. The principle of teleology directs one to continue research as far as possible on the basis of efficient causation. The processes of digestion are not understood by any appeal to the principle that such processes enable the organism to live and thrive. Such processes are understood by accounting for the passage of chemical substances through membranes, but why such membranes permit the passage only of certain chemical substances and no others may not be able to be accounted for on the basis of mechanical causes alone.

Efficient causes are progressive, while final causes are reciprocal. In the former the connection constitutes a series (the so-called causal chain) which is always such that the things which, as effects, presuppose other things as their causes cannot themselves also be causes of these other things. Final causes are that the series involves regressive as well as progressive dependency (a house is the cause of one’s receiving rent money, but the house was built in the first place so that one might receive such rent). Kant calls efficient causes a nexus of real ones and final causes a nexus of ideal ones. The former are also said to determine our knowledge of phenomena. He treats of efficient causation in the Second Analogy of Experience in the “Transcendental Analytic” of the Critique of Pure Reason, where he distinguishes between a subjective connection of cognitions and an objective connection of them. One walks into a warm room and sees a glowing stove. As far as the subjective order of cognitions is concerned, one first feels warm and only later spies the stove concealed behind a screen in the corner. But yet one says that it is the stove which causes the room to be warm and not that it is the warm room which causes the stove to glow. In order to have knowledge through perceptions, one must connect them in their objective time relations. There is no necessity in the subjective order of congnitions, but there certainly is in one’s synthetic reorganization of that order. If event A (glowing stove) precedes event B (warm room) objectively, then one must think of A as preceding B or else be wrong. It makes no difference whether one perceives A first and then B, or B first and then A in his subjective consciousness.

Kant worked out his theory of efficient causation largely in opposition to Hume’s position on the subject. Hume claimed that there are three conditions which two events must fulfill in order for one event to be considered the cause of another: the cause precedes the effect in time, cause and effect are contiguous in space, and cause and effect are found constantly conjoined in experience. Kant leveled his attack mainly against the third condition, but other people have found objections to the first two conditions as well. In the realm of colliding billiard balls, the cause does temporally precede the effect; but in the case of boiling water, the boiling occurs just when the water reaches 100° c.; and so cause and effect are simultaneous. As for spatial contiguity, the moon through empty space attracts the waters of the earth’s seas and oceans to produce tides. In the case of such action at a distance, there is no contiguity in space. As for constant conjunction, some have pointed out that night and day are always conjoined, but night is not the cause of day. Kant objected to the third condition by claiming that on Hume’s view there is no way to distinguish the subjective order of cognitions from the objective order of them.

Hume held that the idea of necessary connection between cause and effect arises when we develop a habit of association from a repeated subjective succession of perceptions (fire always burns). He thus based causation entirely on sensible experience. In contrast, Kant claimed that the objective reordering of the subjective succession of cognitions (which is based on sense perception and imagination) is actually a synthetic reorganization of the a posteriori order of perception. This synthetic reorganization is an a priori act of the human understanding. In other words, the causal ordering of cognitions is an act of the intellect that is brought to experience (or, even better, that makes experience) and is not an ordering derived from experience (as Hume claimed). For Kant in his Critical period the pure concepts of substance, cause, possibility, existence, and necessity were a priori concept that are coterminous with the pure forms of intuition, time and space. Experience is the result of the synthetic activity of the intellect by means of such pure concepts in organizing empirically given sense perceptions that are arrayed in time and space. The history of theories of efficient causation did not end with Kant. The controversy between the a posteriori and a priori views broke out again in the middle of the nineteenth century with the debates between John Stuart Mill and William Whewell. Mill disagreed with Kant, while Whewell agreed. In the twentieth century Bertrand Russell and A. C. Ewing have continued teh debate.

Time, space, matter, force, motion, cause—the major portions of Kant’s philosophy of science have now been examined in terms of these key concepts. This philosophy is rationalistic in comparison with the views of such a later thinkers as Mill and Russell but seems almost empiricistic in comparison with such of Kant’s immediate German idealist successors as Fichte, Schelling, and Hegel. According to Kant, the human mind supplies the form of experience (time, space, and the categories of the understanding); but the content of experience is empirically given in sensation from a source outside the human self (the real material world). The German idealists claimed that the self is the source not only of the form of experience but also of its content. On this view nature becomes a sort of external symbol or image of the self. Nature is the self taken as object. Accordingly, Schelling thought that the whole of physics could be spun out of the mind itself. If so, what need is there for experiment?

The accusation of armchair scientist which Erich Adickes leveled at Kant might more appropriately be directed against these Romantic idealists. Apart from the most general, formal aspects of nature (matter is a continuum and not an interruptum, there is no absolute motion, the changes in nature are causally connected, and so on), all the rest of nature in its particular aspects (temperature of Venus, strength of the gravitational pull of the moon, the cause of diabetes, and so on) must for Kant be learned by experiment. To be sure, he was more interested in the formal aspects than in the particular, but he never claimed that the particular aspects could be dealt with in any way other than by observation and experiment.

The Kantian emphasis on causality in conformity with law and on mathematical rigor in conformity with experience, contributed important elements to the philosophical depth and seriousness that animated the German scientific movement from the middle of the nineteenth century on and that distinguished it from the scientific traditions of other cultures. Two quotations from classic texts will lllustrate the way in which creative German scientists formed their expectations of what a scientific explanation does from their knowledge of Kant. The first, concerning physics, is from Helmholtz’s Ueber die Erhaltung der Kraft (1847), the famous memoir on the conservation of energy which in its philosophical aspect Helmholtz attributed expressly to Kant’s inspiration:

The final goal of the theoretical natural sciences is to discover the ultimate invariable causes of natural phenomena. Whether all processes may actually be traced back to such causes, in which case nature is completely comprehensible, or whether on the contrary there are changes which lie outside the law of necessary causality and thus fall within the region of spontaneity or freedom, will not be considered here. In any case it is clear that science, the goal of which is the comprehension of nature, must begin with the presupposition of its comprehensibility and proceed in accordance with this assumption until, perhaps, it is forced by irrefutable facts to recognize limits beyond which it may not go [from Selected Writings of H. L. F. von Helmholtz, Russell Kahl, ed.(Middletown, Conn., 1971), p. 4].

The second quotation, concerning biology, is from Schwann’s Mikroskopische Untersuchungen über die Uebereinstimmung in der Struktur und dem Wachstume der Tiere und Pflanzen (1839), the equally famous treatise concerning the cellular structure of the living organism. It concludes with a regulatory discussion of methodology deriving from the Kantian distinction between mechanistic and teleological explanation in the Critique of Teleological Judgment;

Teleological views cannot be discarded for the time being since not all phenomena are to be clearly explained by the physical view. Discarding them is not necessary, however, for a teleological explanation is admissible if and only if a physical explanation can be shown to be unattainable. Certainl y it brings science closer to the goal to try at least to formulate a physical explanation. I should like to repeat that when I speak of a physical explanation of organic phenomena, I do not necessarily mean that an explanation in terms of known physical forces like that universal resort, electricity, is to be understood, but rather an explanation in terms of forces which operate like physical forces in service to strict laws of blind necessity, whether or not such forces be found in inorganic nature [Ostwalds Klassiker der Exacten Wissenschaften (Leipzig, 1910), p. 187].

In general, it was in service to the rigorous idealism of Kant that leaders of the first great geneation of German science–including Müller. Schleiden, Mayer, du Bois-Reymond, and Virchow—repudiated the literary and speculative Naturphilosphie of the Romantic idealists, which they dismissed as an episode of cultural wild oats in the adolescence of the German spirit.

In the twentieth century Kant’s thought has not had the direct influence on experimental scientists that it had earlier on Helmholtz and Schwann. But in the philosophy of science Ernst Cassirer gave a Kantian interpretation of the metaphysical and epistemological foundations of relativity in his Einstein’s Theory of Relativity Considered From the Epistemological Standpoint and of quantum theory in his Determinsism and Indeterminism in Modern Physics. C. F. von Weizsäcker gave a Kantian interpretation of quantum theory in his The World View of Physics.

BIBLIOGRAPHY

I. Original Works. The best ed. of Kant’s works is Kants gesammelte Schriften, published by the Royal Prussian Academy of Sciences (Berlin, 1902– ). This ed. already runs to some 27 vols. and, when complete, will contain not only all the published works, letters, and fragments but also all the extant transcripts of lectures.

English translations of some of Kant’s works mentioned in this essay follow, in the order of the publication of the orginal German works: Universal Natural History and Theory of the Heavens, trans. by W. Hastie (Ann Arbor, Mich., 1969), a repr. of Hastie’s Kant’s Cosmogony (Edinburgh, 1900); Kant’s Inaugural Dissertation and Early Writings on Space, trans. by J. Handyside (Chicago, 1929); Critique of Pure Reason, trans. by Norman Kemp Smith, 2nd ed., rev. (London, 1933); Metaphysical Foundations of Natural Sience, trans. by James W. Ellington (Indiana-polis, 1970); Critique of Teleological judgement, trans. nby J. C. Meredith (Oxford, 1928).

II. Secondary Literature. The best biography of Kant is Karl Vorländer, Immamuel Kant, der Mann und das Werk, 2 vols. (Leipzig, 1924). The best in English is J. W. H. Stuckenberg, The life of Immamuel Kant (London, 1882).

The literature about Kant is enormous. Erich Adickes, “Bibliography of Kant,” in The Philosophical Review (1893), lists 2,832 titles and goes only to 1802. The Literaturzeichnisse preceding Kant’s various writings on science and the philosophy of science that are in vol. VII of Karl Vorländer’s ed. of King’s works in the Philosophische Bibliothek series, entitled Kants sämtliche Werke, 10 vols. (Leipzig, 1913–1922), are recommended for books specifcally on King’s works on sciene and the philosophy of science.

A brief list of the works especially relevant to this essay is Erich Adickes, Kants Opus postumum, which is KantStudien, supp. vol. no.50 (Berlin, 1920); and Kant als Naturforscher, 2 vols. (Berlin, 1924–1925); Ernst Cassirer, Substance and Function and Einstein’s Theory of Relativity (Chicago, 1923), pp. 347–456; and Determinism and Indeterminism in Modern Physics (New Haven, 1956); James W. Ellington, introduction and supplementary essay entitled “The Unity of Kant’s Thought in His Philosophy of Corporeal Nature,” in the trans. of the Metaphysical Foundations of Natural Science (see above); Irving Polonoff, Force. Cosmos, Monads, and Other Themes of Kant’s Early Thought, which is Kant-Studien, supp. vol. no. 106 (Bonn, 1972); Lothar Schäfer, Kants Metaphysik der Natur (Berlin, 1966); and C. F. von Weizsäcker, The World View of Physics (Chicago, 1952); and The Relevance of Science (London, 1964).

James W. Ellington