René Descartes posed questions about the nature of knowledge and the nature of being that philosophers still debate today. In Meditations, Descartes expands on his most famous pronouncement, "I think, therefore I am," which first appeared in an earlier text. He explores the idea of the mind as an entity separate from the body—the 'dualist' approach. He also attempts to dispel skepticism—the idea that one cannot truly know anything—and shows that, by doubting everything, we can know some things beyond doubt. Taking point of certainty as his starting point, he discusses a range of subjects and offers a rational proof of the existence of God.