Epistemology

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 alone—including the nature of the intellect itself—is 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 changes—that 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.