cogito ergo sum

René Descartes, who published the phrase in Discourse on the Method, in 1637

The Latin cogito, ergo sum, usually translated into English as "I think, therefore I am", is the "first principle" of the philosophy of the French scientist and philosopher René Descartes. He originally published it in French as je pense, donc je suis in his 1637 Discourse on the Method, so as to reach a wider audience than Latin would have allowed. It later appeared in Latin in his Principles of Philosophy, and a similar phrase (Ego sum, ego existo, 'I am, I exist') also featured prominently in his Meditations on First Philosophy. The dictum is also sometimes referred to as the cogito. As Descartes explained in a margin note, "we cannot doubt of our existence while we doubt." 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."). Antoine Léonard Thomas, in a 1765 essay in honor of Descartes, presented it as dubito, ergo cogito, ergo sum ("I doubt, therefore I think, therefore I am.").