René Descartes is perhaps most remembered for declaring, “I think; therefore, I am.” First published in 1644, Descartes’s Principles of Philosophy elucidates the meaning of those words that ushered in a new era of philosophical thought. Unlike the medieval philosophers who often began by examining the existence and nature of God in a spirit of faith, Descartes begins by reflecting upon himself as one who doubts but who nonetheless desires certain knowledge of God and the world. In setting forth the truths he discovers, Descartes hoped that his Principles of Philosophy would provide a new basis for human knowledge and, most especially, a new footing for scientific inquiry.