French philosophy could be placed and progressively built. Thus he rejected anything which appeared uncertain and decided to only accept apodeictic knowledge as truth. After invoking the possibility of an omnipotent deceiver to reject the external world, the information given to him from his senses, mathematics and logic, Descartes discovered at least one thing could be known apodictically. If he himself was doubting, then he had to exist. Thus Cogito Ergo Sum - I think, therefore I am - became the first principle of Cartesianism. Descartes then claimed that because he discovered the Cogito through perceiving it clearly and distinctly, anything he
Cogito, ergo sum distinctiveness of self-evident propositions — to establish true and justified propositions despite having adopted a method of generalized doubt. As a consequence of this demonstration, Descartes considers science and mathematics to be justified to the extent that their proposals are established on a similarly immediate clarity, distinctiveness, and self-evidence that presents itself to the mind. The originality of Descartes's thinking, therefore, is not so much in expressing the "cogito" — a feat accomplished by other predecessors, as we shall see — but on using the "cogito" as demonstrating the most fundamental epistemological principle, that science and mathematics are justified by