Archimedes used to demand just one firm and immovable point in order to shift the entire earth; so I too can hope for great things if I manage to find just one thing, however slight, that is certain and unshakeable. (2:16; AT 7:24)
BY THE END of the Second Meditation, Descartes has found his “certain and unshakeable” point in his knowledge of his own mind. Famously, he first recognizes that “this proposition, I am, I exist, is necessarily true whenever it is put forward by me or conceived in my mind” (2:17; AT 7:25). He then goes on to form a new conception of himself and to reach absolute certainty about many of his states.
Descartes makes each of these advances by using the method of doubt. As Eudoxus says to Polyander in The Search for Truth, “[I]f you simply know how to make proper use of your own doubt, you can use it to deduce facts which are known with complete certainty” (2:415–16; AT 10:522). What I want to do in this chapter is to explain how Descartes uses his doubt in reaching the conclusions of the Second Meditation. I will be arguing that we need to distinguish among several ways he uses doubt, but that the dominant and indispensable use is the one I described in the previous chapter: to discover conditions that make the First Meditation doubt possible.
In giving this reading of key passages in the Second Meditation, I mean to be picking out only one strand among many that Descartes is weaving together. In highly economical fashion he is at once pursuing the strategy of doubt, with its attendant reform of commonsense thinking, and challenging the preoccupations and assumptions of the scholastic reader, and showing by example what clear and distinct ideas are. Nor is he concerned only with his ideas about himself. In the piece-of-wax passage he