I shall contend that even though Descartes is sometimes certain that he exists, he sometimes doubts that he exists. He believes that two kinds of things exist when he knows that he exists. On the one hand, what exist are occurrent acts of thinking. He knows that they exist because he "observes" them. On the other hand, he believes that what exists is a thinking substance. Such substances are not "observed." They may be known to exist only by establishing that God does not deceive him about the belief that an act of thinking must be in a thinking substance. Thus Descartes's claim to know that he, qua particular thinking substance, exists can be doubted prior to the proofs for the existence and goodness of God. Descartes does exhibit self-doubt in the Third Meditation. My strategy will be to provide and exposition of the view of the self found in the "Synopsis" and again near the end of Meditations. Following this, I shall discuss the doubt of the third Meditation. Initially I establish that in a specified sense Descartes can doubt that he exists. Then I show that he does dobut that he exists. Because my aim is primarily to highlight a particular reading of the text, I shall restrict most comments about several current and different interpretations to footnotes.
Philosophical Review 84 (1):51-69.