Cogito ergo sum (French: Je pense donc je suis; English: "I think, therefore I am"), often mistakenly stated as Dubito ergo cogito ergo sum(English: "I doubt, therefore I think, therefore I am"), is a philosophical statement in Latin used by René Descartes, which became a fundamental element of Western philosophy. The simple meaning of the phrase is that if someone is wondering whether or not they exist, that is in and of itself proof that they do exist (because, at the very least, there is an "I" who is doing the thinking).
Descartes's original statement was "Je pense donc je suis," from his Discourse on Method (1637). He wrote it in French, not in Latin, thereby reaching a wider audience in his country than that of scholars. He uses the Latin "Cogito ergo sum" in the later Principles of Philosophy (1644), Part 1, article 7: "Ac proinde hæc cognitio, ego cogito, ergo sum, est omnium prima & certissima, quæ cuilibet ordine philosophanti occurrat." (English: "This proposition, I think, therefore I am, is the first and the most certain which presents itself to whoever conducts his thoughts in order".). At that time, the argument had become popularly known in the English speaking world as 'the "Cogito Ergo Sum" argument', which is usually shortened to "Cogito" when referring to the principle virtually everywhere else.