It’s a rationalistic a posteriori reflection on the first stage of the process in which Descartes had articulated a state of doubt: logic dictates that if someone doubts something, they must have thought about it. And that if they can think, then they must exist. It is substantially a consideration made in the third person, not in the first, however private the process. The starting point for Descartes is the methodical doubt experienced by a refined intellectual, not the basic experience of a subject.)
