I Can Doubt, Therefore I Am

In the course of attempting to prove that he exists, Descartes constructs an hypothesis, i. e. he explains how X can appear to exist even if it does not; he applies the Principle of Contradiction, i. e. to doubting that he doubts; and, he draws an inference, i. e. from that he does doubt to that he can doubt. Hence, while any of these might be considered question-begging in an attempt to prove that he thinks, rather, they each seem to qualify as self-evidence that he can think. Now, both Sartre and Merleau-Ponty challenge his inference from the indubitability of doubting to the existence of a doubter, because, as they argue, Descartes only demonstrates that doubting, and, therefore, thinking, exists, not that either has a subject. In contrast, throughout the argument, the criterion for 'X exists' is that X, rather than dreaming, hallucinating, etc., is the cause of the appearance of X. And, that one 'can do X' means that one's performance of X is the cause of the appearance of the performance. Likewise, that one is the cause of the performance of X proves that one exists, on the criterion. In other words, merely in showing that he can doubt suffices for Descartes to prove that he exists, a consideration that informs Hegel's analysis of Recognition, via Kant's definition of 'actual'.