René Descartes

"Cogito ergo sum"

i.e. "I think, therefore I am."

- René Descartes, philosopher, mathematician, writer

Descartes was a French philosopher who coined this well-known phrase. Descartes originally wrote it in French ("Je pense donc je suis") and it has since become a fundamental concept in philosophy. Simply put, Descartes reasoned that a person who wonders whether or not he exists must in fact exist by virtue of the fact that he wonders whether or not he exists.