René Descartes made significant contributions to philosophy, notably in developing rationalism and analytical geometry. His famous statement, "Cogito, ergo sum" ("I think, therefore I am"), emphasizes the role of doubt and reason as foundational to knowledge. Descartes' method of systematic skepticism encourages questioning established beliefs, laying groundwork for modern scientific inquiry. Additionally, his work in mathematics introduced Cartesian coordinates, revolutionizing the study of geometry and linking it with algebra. Descartes' influence extends beyond philosophy; his ideas about dualism and the mind-body relationship continue to spark debates in psychology and metaphysics.