Descartes's Cogito and the Problem of Presupposition of Substance

This essay intends to discuss the famous proposition I think, therefore I exist, with a critical approach. At first, some preliminaries will be said concerning Descartes’s general way in his epistemological system, which can be called methodic doubt and then we will give an account of the two well-known general approaches to the interpretation of this proposition among Descartes’s interpreters: inferential approach and intuition's. In this inquiry, Focusing on Meditations and considering evidences from other works of Descartes, we will attempt to give an account of Descartes’s view on the problem of I and also his own doctrines about thought and existence of I. It seems that Descartes' system of knowledge suffers a gap in justifying coexistence of consciousness with perception of thoughts and ideas and their being belonged to a single subject. The claim of the main part of the essay is that, opposed to his methodological demands, Descartes has laid down as a principle the a priori knowledge of the nature of self and has a particular presupposition about I: I as a substance with certain attributes. We called this the problem of the presupposition of substance. In fact, the substance-quality structure have a tacit but effective activity in Descartes’s system of knowledge at depth. The present essay is an attempt to make explicit this fact by investigating inconsistency in application of Descartes' method، and also some semantic difficulties of "I" in Cogito Ergo Sum.