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 one's belief in their own existence would be secure, for there is no way one could be deceived unless one existed in order to be deceived. But I have convinced myself that there is absolutely nothing in the world, no sky, no earth, no minds, no bodies. Does it now follow that I, too, do not exist? No. If I convinced myself of something [or thought anything at all], then I certainly existed. But there is a deceiver of supreme power and cunning who deliberately and constantly deceives me. In that case, I, too, undoubtedly exist, if he deceives me;