I think; therefore I am

A statement by the seventeenth-century French philosopher René Descartes. “I think; therefore I am” was the end of the search Descartes conducted for a statement that could not be doubted. He found that he could not doubt that he himself existed, as he was the one doing the doubting in the first place. In Latin (the language in which Descartes wrote), the phrase is “Cogito, ergo sum.”