I Think, Therefore I Am

The Latin cogito, ergo sum, usually translated into English as “I think, therefore I am”, is the “first principle” of René Descartes’s philosophy. He originally published it in French as je pense, donc je suis in his 1637 Discourse on the Method. It later appeared in Latin in his Principles of Philosophy, and a similar phrase also featured prominently in his Meditations on First Philosophy.

In the posthumously published The Search for Truth by Natural Light, he expressed this insight as dubito, ergo sum, vel, quod idem est, cogito, ergo sum (“I doubt, therefore I am – or what is the same – I think, therefore I am”).