A philosophical statement used by Rene Descartes, which became a foundational element of Western philosophy. The simple meaning of the phrase is that if someone is wondering whether or not he exists, that is in and of itself proof that he does exists. Descartes argues that the statement is indubitable, because even if an all-powerful demon were to try to deceive me into thinking that i exist when i do not, i would have to exist for the demon to deceive me. Therefore, whenever i think, i exist.
