Cogito, ergo sum

Meditation II opens in the rubble left by the three waves of doubt. Descartes looks for a single fixed point, “one thing, however slight, that is certain and unshakeable” — recalling Archimedes, who asked only for one firm place to stand in order to move the whole earth. He finds it not by escaping the doubt but by turning the doubt back on itself.

The move is this: suppose the demon is deceiving me about everything. Then he must be deceiving someone — and that someone is me. “Let him deceive me as much as he can, he will never bring it about that I am nothing, so long as I think I am something” (Meditation II). To be deceived, I must exist. So the proposition “I am, I exist” (ego sum, ego existo) is necessarily true whenever I assert or conceive it.

Notice the certainty’s strange shape: it is self-verifying but momentary. “I exist” is guaranteed true only while I am thinking it. “For it could be that were I to cease all thinking I would then utterly cease to exist” (Meditation II). The cogito is a certainty renewed each time it is entertained, not a stored fact I can lean on while asleep. This is why so much still hangs on it — it is bedrock, but a bedrock I must keep touching.

The next question: I know that I am — but what am I? Descartes strips away every answer that presupposes the body, since the body is still in doubt. He can doubt he has a body; he cannot doubt that he thinks. So whatever he is, he is essentially a thing that thinks — res cogitans (a thinking thing). “I am, then, a thing that thinks” — and he unpacks thinking broadly: “a thing that doubts, understands, affirms, denies, is willing, is unwilling, and also imagines and senses” (Meditation II).

From this Descartes draws a startling comparative claim: the mind is better known than the body (the title of Meditation II). Everyone assumes bodies — solid, visible, touchable — are the clearest things there are, and the mind a foggy afterthought. Descartes means to overturn exactly this. He proves it with a homely example: a piece of wax.

The wax argument. Take a fresh piece of honeycomb wax. It smells of flowers, tastes of honey, is cold, hard, and makes a sound when tapped. Now hold it to the fire. Every one of those sensory qualities changes: the smell fades, the taste goes, it turns hot, liquid, shapeless, silent. Yet everyone agrees the same wax remains (Meditation II). So what I grasp as “the wax” cannot be any of those sensory qualities — they have all been replaced.

What is left constant, then? Only that the wax is something extended, flexible, and changeable — able to take on countless shapes and sizes. But I cannot imagine all those countless shapes (imagination runs out), and I never sensed them (they hadn’t happened yet). So my grasp of the wax’s real nature comes not from the senses and not from imagination but from the intellect alone — a “purely mental scrutiny” (inspectio mentis). I judge “there is the wax” by understanding, not by seeing.