"I think, therefore I am." Rationalist philosopher and mathematician René Descartes, considered the father of modern philosophy, held this as self-evidently true. In this program, world-renowned author and professor Bryan Magee and Bernard Williams of Kings College examine Descartes’s theory of knowledge and his use of skeptical inquiry to affirm reality, including the existence of God. Descartes’s theory of physical and mental substances, and Cartesian dualism—which allows the concept of science to coexist with the notion of God—are also examined.