Although he is best known to history as the man who said “I think, therefore I am” – René Descartes was not merely a philosopher but also a mathematician. If you’ve ever used an X-Y coordinate system, you’ve used one of his most famous inventions, the Cartesian plane.
A Frenchman who spent most of his adult life in Holland, Descartes’ major contributions to philosophy were in the field of metaphysics – the mind-body problem. Descartes’ answer to the problem was dualism – that mind and body are separate. In mathematics, the Cartesian coordinate system married algebra and geometry, and created the theoretical basis upon which Leibniz and Newton each independently built calculus.