Meditation 6 — Of the Existence of Material Things

Descartes begins by noting that material objects can at least exist, since God could produce whatever he can clearly and distinctly conceive. But can he prove they do exist? He examines the faculties of imagination and pure intellection. When he imagines a triangle, he not only conceives it but applies his mind to it with a kind of interior gaze — he seems to see it. When he thinks of a chiliagon (a thousand-sided figure), he can clearly conceive it but cannot really imagine it. The difference suggests that imagination depends on something distinct from the mind alone — presumably the body. This is not a proof, but a clue.

The real argument for bodies comes from the analysis of sense perception. He has a powerful and almost irresistible inclination to believe that his ideas of sensible things come from bodies outside him. God has given him this inclination and has given him no faculty to detect that it is wrong. A non-deceiving God would not produce in us a strong and natural inclination toward a false belief and then provide no means to correct it. Therefore bodies must really exist — though perhaps not exactly as they appear, since the senses are better at reporting what is useful than at reporting precise scientific truths.

From this foundation Descartes establishes the real distinction of mind and body: he has a clear and distinct idea of himself as only a thinking, non-extended thing, and a clear and distinct idea of body as only an extended, non-thinking thing; what is clearly and distinctly conceived as separable, God can separate; therefore mind and body are really distinct substances. But immediately the complication: I am not merely in my body like a pilot in a ship. I feel pain when the body is injured; I feel hunger and thirst; I feel pleasure. These sensations are not cool reports but confused urgencies that arise from a genuine union of mind and body. How a non-extended thinking thing and an extended non-thinking thing are united in a single person — this question, which Princess Elisabeth pressed on Descartes in 1643, he does not answer here. The Sixth Meditation ends with the observation that the senses are trustworthy enough for practical life, even if not for science. The world is real. The doubt is over. And the problem of mind and body — named here with perfect precision — has been open ever since.