I think, therefore I am. While I was trying in this way to think everything to be false it had to be the case that I, who was thinking this, was something. (1637)
Descartes is seen as the father of modern philosophy. Mainly because instead of God, he gave mankind a central place in our thinking. He looks for something that he can state with absolutely certainty. He discovers that his only certainty is that he himself exists: ‘I think, therefore I am’. Starting from this basis, he can expand his thinking. You can read where he ends up at the second tile about Descartes.