Meditation 1 — Of the Things of Which We May Doubt

Several years have passed, Descartes says, since he first noticed that he had accepted many false opinions as true, and that everything he had built on them was therefore uncertain. He has been waiting for a moment to remedy this; now is the time. He does not need to refute each belief individually — he only needs to find, in each category of belief, some reason for doubt, and the whole category falls.

First he attacks beliefs based on the senses. The senses sometimes mislead us. Prudence requires not trusting wholly what has once deceived. But surely, he objects to himself, I cannot doubt that I am here, seated by the fire, holding this paper? Yet sometimes in dreams he has had equally vivid impressions of being in his room, only to wake and find it was not so. There is no reliable mark by which waking can be distinguished from dreaming. Even if the dream argument threatens our knowledge of particular objects, surely mathematics survives? Two and three make five whether I am asleep or awake.

Then comes the third and decisive move: the evil deceiver. What if, instead of a benevolent God, there is a supremely powerful and malicious spirit whose entire purpose is to deceive me — who has so constructed my nature that I err even in what seems most evident, including simple arithmetic? At this point Descartes has found a reason to doubt everything, and the demolition is complete. He ends by resolving to hold to this doubt artificially — to treat all familiar beliefs as if they were false — so that when he searches for something the doubt cannot reach, he will be sure he has found it.