Cogito ergo sum

"Cogito ergo sum( I think, therefore I am) is a philosophical statement in Latin by Rene 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) - Source: Wikipedia