Descartes Was Half Right — and the Half He Got Wrong Matters More

Every year I teach the Meditations, and every year I am struck by how close Descartes came to getting something exactly right — and how the small distance he missed has cost us four hundred years of confusion.

The Cogito — cogito ergo sum, I think therefore I am — is one of the most audacious arguments in the history of philosophy. By the end of the Second Meditation, Descartes has established (to his own satisfaction and, for a moment, to ours) that the one thing he cannot doubt is that there is doubting going on. Whatever else the evil demon has deceived him about, the deception itself requires a thinker.

The argument is brilliant. It is also, I now think, subtly equivocal — and the equivocation has mattered enormously.

The Equivocation

Descartes moves from “there is thinking” to “I am a thinking thing.” The first claim is almost undeniable. The second smuggles in something more.

“There is thinking” is compatible with thinking being an event with no persistent subject — a flash of experience without a self attached. Buddhism has long maintained something like this: that what we call the self is a construction built over a stream of momentary experiences, none of which contains a self.

Descartes assumes that if there is thinking, there must be a thinker — a substance, a res cogitans, something that persists through and underlies the mental events. But this is not forced by the logic. It is a grammatical intuition masquerading as a metaphysical necessity.

Why It Matters

If Descartes had paused here — if he had said “I have established that there is thinking, and nothing more” — the subsequent history of mind-body theory might have looked very different.

Instead, by the time he reaches the Sixth Meditation, he has a fully-formed immaterial substance — the mind — that must somehow interact with the body. And the problem of how two completely different kinds of substance interact has plagued philosophy of mind ever since.

The hard problem of consciousness is, in part, Descartes’s revenge. We inherited a picture on which the mental and the physical are categorically different, and we have been trying to bridge that gap ever since.

The lesson I draw is not that Descartes was foolish — he was anything but — but that our deepest assumptions are often invisible to us precisely because they feel like obvious logical steps.