Descartes' "I think, therefore I am" comes from his 1637 work Discourse on the Method. The idea is that the act of doubting or thinking is itself proof of one's existence. It's the starting point of his entire philosophical system: the one thing that can't be doubted is that there's a mind doing the doubting.
A commonly missed detail: Descartes wrote it in French, not Latin. The original line is "je pense, donc je suis." The famous Latin version, "Cogito, ergo sum," came from a later translation. The Discourse was written in French precisely because Descartes wanted it to be accessible beyond the Latin-reading academic world.
Descartes' "I think, therefore I am" comes from his 1637 work Discourse on the Method. The idea is that the act of doubting or thinking is itself proof of one's existence. It's the starting point of his entire philosophical system: the one thing that can't be doubted is that there's a mind doing the doubting.
A commonly missed detail: Descartes wrote it in French, not Latin. The original line is "je pense, donc je suis." The famous Latin version, "Cogito, ergo sum," came from a later translation. The Discourse was written in French precisely because Descartes wanted it to be accessible beyond the Latin-reading academic world.