Descartes: Doubt and Certainty

9.1 The Pursuit of Knowledge

Given the upheaval in traditional ideas and attitudes, and established religious doctrines, skepticism began to take hold in the early modern period. Descartes seeks to combat that by establishing a solid foundation for the sciences. This means, among other things, finding an epistemological method that would secure such a foundation. More specifically, Descartes is interested in securing the truth of our propositional knowledge. Rather than take an a posteriori approach, Descartes sets out to show, a priori, that such knowledge is possible.

9.2 Plato’s Rationalism

Following Parmenides, Plato privileges rationalism over empiricism, or reason over the senses, as the way we know. Unaided by the senses, reason will come to contemplate the Forms.

9.3 Descartes’s Doubt

Descartes’s skeptical method is enlisted to achieve certainty—“certain and indubitable” knowledge. This method involves first assuming all beliefs based on sense experience are false. This leads him through the dream argument, where he concludes not only that he cannot find a way out of the dream supposition, but also that other beliefs, such as mathematical ones, may be false. The extension of the doubt to purely rational beliefs is brought on by the supposition of an evil genius. The doubt becomes hyperbolic at this point, and brings him to the cogito of Meditation II.

9.4 Descartes’s Certainty

Descartes doubts everything: external world, his own body, his own existence. Then he wonders how, under these conditions, he could doubt his existence. Indeed, he can doubt there is a world, and that he has a body, but can he doubt his existence entirely? Perhaps not, and if that’s the case, then he has convinced himself of something. Nevertheless, what if the evil genius is deceiving him into believing he exists? “Then without doubt I exist also if he deceives me, and let him deceive me as much as he will, he can never cause me to be nothing so long as I think that I am something.”

Descartes has his one certainty: he exists as a thinking thing. This is his identity, and it is true, so far as he knows, only when he thinks, “for it might possibly be the case if I ceased entirely to think, that I should likewise cease altogether to exist.” At this point, however, he doesn’t know what that means—he doesn’t know what this thinking thing is. He has to be careful, too, since he is not sure what follows from this one truth.

As he further examines what it is to be “a thing which thinks,” he finds it involves “doubting, understanding, affirming, denying, willing, refusing, imagining, and feeling.” He is inclined to believe he has a body, though not only has he no proof of this, it’s also odd that this inclination persists despite how dubious it is to consider. All he knows that is real is himself as a thinker—immaterial substance.

Though this is all Descartes is certain of, his “mind loves to wander,” which means that it loves to believe in corporeal objects. So, he decides to consider material objects to see what he learns. Here we arrive at the wax argument.

When considering a piece of wax through various changes, he wants to know what it is in the wax that compels him to assert it is the same despite various changes sensed and (mentally) pictured. He realizes (1) it’s not any sensory quality, since all those change. Moreover, (2) it’s not that he maintains an image of it through all its changes—he couldn’t possible “compass the infinitude” of physical alterations. He concludes that (3) it is “an intuition of the mind” that tells him the wax is the same, even though the language used suggests the senses. This intuition is a judgment drawn from the act of seeing, just as he judges that the men below his window are not mere automatons. Specifically, his judgment determines the wax is the same. Sense perception, imagination, and judgment, then, are different modes of thinking.

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