"I think, therefore I am"

Cogito ergo sum (French: "Je pense donc je suis"; English: "I think, therefore I am") is a philosophical Latin statement proposed by René Descartes [1]. The simple meaning of the phrase is that someone wondering whether or not he or she exists is, in and of itself, proof that something, an "I", exists to do the thinking. However, this "I" is not the more or less permanent person we call "I". It may be that the something that thinks is purely momentary, and not the same as the something which has a different thought the next moment.

A common mistake is that people take the statement as proof that they, as a human person, exist. However, it is a severely limited conclusion that does nothing to prove that one's own body exists, let alone anything else that is perceived in the physical universe. It only proves that one's conciousness exists (that part of an individual that observes oneself doing the doubting). It does not rule out other possibilities, such as waking up to find oneself to be a butterfly who had dreamed of having lived a human life.

Descartes's original statement was "Je pense donc je suis", from his Discourse on Method (1637). He wrote it in French, not in Latin and thereby reached a wider audience in his country than that of scholars.

[1] René Descartes (1596 – 1650) was a French philosopher, mathematician, and writer who spent most of his adult life in the Dutch Republic. He has been dubbed the 'Father of Modern Philosophy', and much subsequent Western philosophy is a response to his writings.

“ And so something which I thought I was seeing with my eyes is in fact grasped solely by the faculty of judgment which is in my mind. ”