René Descartes, (born March 31, 1596, La Haye, Touraine, France-died February 11, 1650, Stockholm, Sweden), French mathematician, scientist, and philosopher. Because he was one of the first to abandon Scholastic Aristotelianism, because he formulated the first modern version of mind-body dualism, from which stems the mind-body problem, and because he promoted the development of a new science grounded in observation and experiment, he has been called the father of modern philosophy. Applying an original system of methodical doubt, he dismissed apparent knowledge derived from authority, the senses, and reason and erected new epistemic foundations on the basis of the intuition that, when he is thinking, he exists; this he expressed in the dictum "I think, therefore I am" (best known in its Latin formulation, "Cogito, ergo sum," though originally written in French, "Je pense, donc je suis"). He developed a metaphysical dualism that distinguishes radically between mind, the essence of which is thinking, and matter, the essence of which is extension in three dimensions. Descartes's metaphysics is rationalist, based on the postulation of innate ideas of mind, matter, and God, but his physics and physiology, based on sensory experience, are mechanistic and empiricist. Descartes's Discourse on Method (1637) is one of the first important modern philosophical works not written in Latin. Descartes said that he wrote in French so that all who had good sense, including women, could read his work and learn to think for themselves. He believed that everyone could tell true from false by the natural light of reason. In three essays accompanying the Discourse, he illustrated his method for utilizing reason in the search for truth in the sciences: in Dioptrics he derived the law of refraction, in Meteorology he explained the rainbow, and in Geometry he gave an exposition of his analytic geometry. He also perfected the system invented by François Viète for representing known numerical quantities with a, b, c, ..., unknowns with x, y, z, ..., and squares, cubes, and other powers with numerical superscripts, as in x2, x3, ..., which made algebraic calculations much easier than they had been before. In the Discourse he also provided a provisional moral code (later presented as final) for use while seeking truth: (1) obey local customs and laws, (2) make decisions on the best evidence and then stick to them firmly as though they were certain, (3) change desires rather than the world, and (4) always seek truth. This code exhibits Descartes's prudential conservatism, decisiveness, stoicism, and dedication. The Discourse and other works illustrate Descartes's conception of knowledge as being like a tree in its interconnectedness and in the grounding provided to higher forms of knowledge by lower or more fundamental ones. Thus, for Descartes, metaphysics corresponds to the roots of the tree, physics to the trunk, and medicine, mechanics, and morals to the branches.