Epistemology: Early Modern

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Epistemology: Early Modern

Modern philosophy is generally thought to be distinguished by an "epistemological turn." Prior philosophical tradition accorded special status to metaphysics, or "first philosophy" (the general philosophical investigation into the nature of reality). The modern tradition, by contrast, holds that it is necessary to determine the nature and bounds of human knowledge before any sure advance into metaphysics can be achieved.

Modern epistemologies are traditionally sorted out as "rationalist" or "empiricist." According to the rationalist position, the intellect is the foundation of all human knowledge, including knowledge of the material world; the classic expression of rationalism in the modern era is found in the philosophy of René Descartes (15961650), who took a cue from Plato and held that the senses are detrimental to true knowledge. But according to the empiricist position, sense experience is the foundation of knowledge. Much of the development of empiricism in the early modern era involved the purification of its principles through the removal of vestigial traces of Cartesian rationalism; this purification reached its pinnacle in the philosophy of David Hume (17111776). The "critical philosophy" of Immanuel Kant (17241804) is generally regarded as the culmination of the modern tradition, since it arose out of an assessment of the shortcomings of both empiricism and rationalism, and a synthesis of their insights.

Defining the Modern Tradition: Cartesian Beginnings

It is convenient to point to Descartes's Meditationes de prima philosophiae (1641; Meditations on first philosophy) as the inauguration of modern philosophy, since it advertises its project as making a radical break with the Aristotelian-scholastic tradition. "Some years ago," its narrator begins, "I was struck by the large number of falsehoods that I had accepted as true in my childhood, and by the highly doubtful nature of the whole edifice that I had subsequently based upon them" (Philosophical Writings, vol. 2, p. 12). The meditator's first task is the "general demolition" of all of his "opinions"; this is necessary, he claims, in order to establish the foundations of scientific knowledge.

Since a central tenet of the rejected Aristotelian-scholastic tradition is the empiricist thesis that "nothing is in the intellect that was not first in the senses," the work of mediation is conceived as a radical withdrawal from the senses. Through it, the mind is supposed to find itself "in its own freedom" and to "distinguish without difficulty what belongs to itself, i.e., to an intellectual nature, from what belongs to the body" (p. 9). Mind and physical body, according to Descartes, are the two kinds of reality or "substance." The essence of mind is thinking; it is fundamentally active and self-determining. The essence of body is to be extended, or to take up space; it is fundamentally passive, and the state of one body is determined solely through its relation to other bodies. The Meditationes are supposed to demonstrate that humans have better knowledge of the mind than of any material body: the first certainty established after the "general demolition" of the meditator's former opinions is the certainty of his own existence as a "thinking thing."

According to Descartes, whatever can be known through the intellect aloneincluding the nature of the intellect itselfis known "clearly and distinctly." The famous experiment with a piece of wax in the Second Meditation is supposed to show that humans know the nature of body by means of the intellect as well. On the basis of sense experience, one can appreciate the color, texture, smell, and size of the piece of wax; but these determinations are known only in an "imperfect and confused" manner, since they all undergo alteration as the wax is brought nearer the fire. One can have "clear and distinct" knowledge only of the material substance that underlies these changesthat is, "merely something extended, flexible and changeable" (p. 20).

Although Descartes's conception of mind and its essential distinctness from body is not itself a universally shared theory of modern philosophy, it nevertheless sets out a problem with which the entire ensuing tradition must deal. To understand how that unfolds, it will be helpful to consider three central concerns of early modern philosophy in general: its "mechanistic" conception of nature, the theory of sense perception that is tied to that conception of nature, and skepticism.

Nature as Mechanism

The root of the modern conception of nature lies in Descartes's idea that there are but two kinds of substance: spiritual substance (mind) and material substance (body). Since the essence of body is extension, and extension can be determined quantitatively, mathematics is the language of nature. The modern conception of nature departs from the Aristotelian-scholastic conception, which placed heavy emphasis on teleological explanation. According to this view, distinct principles determine the character or essence of different kinds of things in nature (or "natural kinds"); each kind of thing is driven, as it were, to express its "nature" according to its principle. In contrast, the modern mechanistic view deemphasizes the importance of determining natural kinds, focusing instead on universal laws of the motion of matter.

The natural philosopher Robert Boyle (16271691) and others charged that the Aristotelian framework was unable to yield satisfying explanations of natural phenomena. As Boyle developed his account, he advanced a hypothesis about minute particles of matter called "corpuscles": according to the "corpuscular philosophy," particular phenomenaincluding the appearance of qualities like colorcan, in theory, be explained in terms of the arrangement and motion of these atoms. The theory of corpuscles was merely a hypothesis advanced on the recommendation of its explanatory power: "corpuscles" were theoretical entities, which had not been perceived even with the aid of instruments.

Theory of Sense Perception

The early modern theory of sense perception combined aspects of the mechanistic conception of nature with the Cartesian dualism of mind and body. Sense representations are "ideas," things proper to the immaterial mind; they are caused by qualities that are attributed to material bodies. It was thought to be possible, at least in principle, to give a mechanistic account of how a particular arrangement of the corpuscular micro-structure brings aboutthrough the motion of bodiesa certain "impression" on our sensory organs. But without overcoming the problematic of Cartesian dualism, no satisfying explanation of how some such physical impact (an "impression") could yield something mental (an "idea"). John Locke (16321704), an empiricist philosopher who ambivalently accepted aspects of Cartesian dualism, claimed in his Essay concerning Human Understanding (1690) that one must "take notice" of impressions in order to enjoy ideas of sense or have any sense perception at all (book 2, chapter 5). This capacity of the mind to "take notice" of impressions thus figures as an unexplained explainer in Locke's philosophy.

Descartes and Locke both thought that unnoticed judgments play an important role in sense perception. This again has to do with the Cartesian conception of the mind: the mind is transparent to itself, having infallible awareness of its own contents, or "ideas." People err only when they make judgments about the world on the basis of these ideas. To account for this, Descartes distinguishes between the understanding, which is simply an active capacity to be conscious of the mind's ideas, and the will, which affirms or denies that certain relations of ideas represent states of affairs in the world. For Descartes, judgment involves an act of the will. Although Locke denies Descartes's view about the role that the will plays in judgment, he agrees that unnoticed and habitual judgments play an important role in perception. When looking at a sphere of a uniform color, Locke claims, "the Idea thereby imprinted on our Mind, is of a flat Circle variously shadow'd"; but a habitual judgment "alters the Appearances into their Causes" so that what is perceived is "a convex Figure, and an uniform Colour" (p. 145).

Skepticism and the Cartesian Framework

The Cartesian meditative project invites a skeptical worry about the existence of the external world, for when the mind withdraws from the senses, it cuts itself off from the material world altogether. Indeed, in order for the narrator of the Meditationes to achieve his goal of razing the edifice of all of his former opinions, he must deliberately cultivate a radical form of skepticism, accepting the possibility that his ideas do not represent any independent material reality but may instead be the work of a "malicious demon." By the end of the Meditationes, the existence of the external world is supposed to have been established through a proof of the existence of God, which is in turn supposed to yield results about the reliability of the meditator's cognitive faculties (on the testimony of which the meditator supposes that there is a world independent of his mind).

Philosophers after Descartes continued to struggle with the fact that the Cartesian framework compels one to conclude that perception does not put us in direct contact with the outside world. One has contact with the world only through a "veil of ideas," and it seems one can only infer the presence of an external, independent, material world.

George Berkeley (16851753) tried to defend common sense against this skeptical worry by advancing an idealist account of perception in Three Dialogues between Hylas and Philonous (1713). His account is "idealist" because it argues that there is no mind-independent reality. At bottom Berkeley disputes the coherence of the Cartesian conception of material substance. Building on the premise that one cannot represent any physical object without having "ideas" of its qualities, he argues that objects are identified by the constant conjunction of certain ideas: "Take away the sensations of softness, moisture, redness, tartness, and you take away the cherry. Since it is not a being distinct from sensations; a cherry, I say, is nothing but a congeries of sensible impressions" (p. 130). The cause of these ideas cannot be material substance, Berkeley argues, but only the mind of God. Berkeley's curious defense of common sense comes down to a denial that there is any reality independent of "mind" at all.

The Scottish philosopher Thomas Reid (17101796) saw more clearly than any of his predecessors that skepticism about the "veil of ideas" is the unavoidable result of any adherence to the dominant modern theory of perception. He argues so at length in An Inquiry into the Human Mind, on the Principles of Common Sense (1764) and Essays on the Intellectual Powers of Man (1785) and offers a new account of perception that is not based on the modern "way of ideas." Although Reid was largely neglected by historians of philosophy for most of the twentieth century, his account of perception has received greater attention since the mid-1990s as a source of philosophical insight in its own right.

Humean Skepticism

Hume's epistemology is quite unencumbered by skeptical worries about the existence of the physical world. However, Hume's philosophical preoccupations are shaped by a new kind of skepticism, which is most clearly expressed in the Enquiry concerning Human Understanding (1748).

For Hume, the problem of epistemology is justificatory: it must be established how people take themselves to have knowledge of the causal order of nature. For "nature," Hume remarks, "has kept us at a great distance from all of her secrets, and has afforded us only the knowledge of a few superficial qualities of objects; while she conceals from us those powers and principles, on which the influence of these objects entirely depends" (Enquiry, §4, p. 21).

The problem Hume identifies can be traced back to Locke, who noted that people do not have knowledge of the corpuscular microstructure of things (see Essay, book 4, chapter 3). They have knowledge only of the "nominal essence" of things; in other words, humans identify natural kinds on the basis of observable qualities that are constantly conjoined in experience, but since they cannot give an account of the corpuscular microstructure that allows them to observe these qualities, they do not have knowledge of the "real essence" of things. Hume generates a skeptical worry out of this: given that one has no cognitive access to the "secret nature" of things, then for all one knows this "secret nature" could change without any alteration in the observable properties of things. Hume recognizes that ordinary human cognitive practices carry on without people becoming encumbered by this skeptical worry. Yet "as a philosopher," he wonders: On what basis do we infer that the regular course of our experience should be a guide to determining a necessary connection of events observed in nature?

Hume responds to his "skeptical doubts" with a "skeptical solution" (Enquiry, §§45). People are able to make causal determinations only in a "subjective" fashion. In the course of experience, human minds are shaped by repetitions in circumstances. The result is the formation of tacit expectations, or anticipatory dispositions, which Hume calls "customs." These anticipatory dispositions are formed mechanically through associations of the imagination. The necessary connection thought in the concept of cause is merely something that "we feel in the mind, this customary transition of the imagination from one object to its usual attendant" (Enquiry, §7, p. 50). This "sentiment," Hume argues, is the source of the concept of causality. Thus Hume ends up with the following view. It cannot be said that one thing (A) brings about an effect in another thing (B); it may be said that representations of A are customarily conjoined with representations of B. Thus the necessity thought in the concept of cause is merely subjective: when faced with an event of type A, a subject cannot help but to anticipate an event of type B.

Kant's Critical Philosophy

Philosophy in Germany in the late seventeenth and early eighteenth centuries was largely dominated by the legacy of the rationalist philosopher G. W. Leibniz (16461716), but by the middle of the eighteenth century German philosophers were increasingly well read in the empiricist philosophy of Locke and Hume. Kant's mature philosophy, advanced in his Kritik der reinen Vernunft (1781, rev. 1787; Critique of pure reason) and presented in a "popular" form in his Prolegomena (1783), is generally thought to be a critical synthesis of these two traditions.

Hume's skeptical worries focused Kant's attention on the nature of scientific knowledge. For Kant, the very idea of such knowledge rests on a presupposition that humans can have cognitive access to laws (as opposed to mere regularities) of nature. Given the viability of scientific knowledge, Kant supposes, one must be in the possession of certain concepts on the basis of which one can combine representations independently of experience. One such concept is "cause and effect." But Hume's attempt to account for the concept of causality within a skeptical, empiricist framework required that he hold that genuine laws of nature are cognitively inaccessible. Hume's skeptical worries, Kant famously remarked, "first interrupted my dogmatic slumber" (Schriften, vol. 4, p. 260); but Hume's skeptical solution was not a happy one for Kant, who never doubted human capacity for genuine scientific knowledge.

In the Critique, Kant is particularly interested in the questionable status of metaphysics as a science. The first words of the book attest to the "peculiar fate" of human reasonnamely, that it is compelled to ask questions that are beyond its capacity to answer. Kant principally has in mind the classic questions of metaphysics: for example, whether the soul is simple or composite or whether the world is finite or infinite. Reconceiving of what the proper task of metaphysics should be, Kant takes a cue from the flourishing science of Newtonian physics. But while the goal of physics is to explain some particular array of phenomena, the goal of metaphysics is to give an account of nature as such. For Kant, metaphysics begins with an exhaustive account of human cognitive capacity as the source of the fundamental principles that determine what it is to figure in the domain of nature at all. The main argument of the Critique is a demonstration of the relevant principles, which Kant takes to be the basis of the laws of nature.

See also Epistemology: Ancient ; Epistemology: Modern ; Idealism ; Kantianism ; Skepticism .


Berkeley, George. Three Dialogues between Hylas and Philonous. Edited by Jonathan Dancy. Oxford and New York: Oxford University Press, 1998.

Boyle, Robert. Selected Philosophical Papers of Robert Boyle. Edited by M. A. Stewart. Manchester, U.K.: Manchester University Press, 1979.

Descartes, René. Oeuvres de Descartes. Edited by Charles Adam and Paul Tannery. New ed. 11 vols. Paris: CNRS/Vrin, 19741986. The standard edition of Descartes's works, in the original Latin and French.

. The Philosophical Writings of Descartes. Translated by John Cottingham, Robert Stoothoff, and Dugald Murdoch. 3 vols. Cambridge, U.K.: Cambridge University Press, 19841991. The standard edition of Descartes's works in English translation.

Hume, David. An Enquiry concerning Human Understanding. Edited by Eric Steinberg. Indianapolis and Cambridge, U.K.: Hackett 1977.

. Treatise of Human Nature. Edited by L. A. Selby-Bigge and P. H. Nidditch. 2nd ed. Oxford: Clarendon 1978. Although the Enquiry concerning Human Understanding is largely a restatement of book 1 of the Treatise, it is generally thought to contain the more emphatic expression of Hume's skeptical position.

Kant, Immanuel. Critique of Pure Reason. Translated by Paul Guyer and Allen W. Wood. Cambridge, U.K.: Cambridge University Press, 1997.

. Gesammelte Schriften. Edited by the Königlich Preussischen Akademie der Wissenschaften, later the Deutschen Akademie der Wissenschaften zu Berlin. 29 vols. Berlin: Walter de Gruyter, 1900. The standard edition of Kant's works, in the original German and Latin.

. Prolegomena to Any Future Metaphysics That Will Be Able to Come Forward as Science. New ed. Translated by Paul Carus and revised by James W. Ellington. Indianapolis and Cambridge, U.K.: Hackett, 1977.

Locke, John. An Essay concerning Human Understanding. Edited by Peter H. Nidditch. Oxford: Clarendon, 1975.

Reid, Thomas. Essays on the Intellectual Powers of Man. Edited by Derek R. Brookes. Edinburgh: Edinburgh University Press, 2002.

. An Inquiry into the Human Mind on the Principles of Common Sense. Edited by Derek R. Brookes. Edinburgh: Edinburgh University Press, 1997.

Melissa McBay Merritt