I think, therefore I am

Meanings

1. I am able to think, therefore I exist; a proof of existence based on the fact that someone capable of any form of thought necessarily exists.

Etymology

Calque of French je pense, donc je suis or perhaps of Latin cōgitō, ergō sum. First written in French by René Descartes, a 17th century French philosopher, in Discourse on the Method (1637) as je pense donc je suis, which he later expressed in Latin in Principles of Philosophy (1644).