At the end of the first meditation, Descartes seeks one fact of which he can be certain and in "cogito ergo sum", he manages to reach the following conclusions: 1) Whatever thinks exists
2) I think.
Therefore 3) I exist.
In fact, this concept is stated at the beginning of his second meditation as follows, "I have convinced myself there is absolutely nothing in the world, no sky, no earth, no minds, no bodies. Does it follow now that I don't exist either? No. If I persuaded myself of anything, then certainly I existed. But there is a deceiver of supreme power and cunning who deliberately and constantly deludes me. In that case, too, I undoubtedly exist, if he is deceiving me. And let him deceive me to his heart's content, he will never bring it