born March 31, 1596, La Haye, Touraine, France
died Feb. 11, 1650, Stockholm, Swed.
French mathematician, scientist, and philosopher, considered the father of modern philosophy.
Educated at a Jesuit college, he joined the military in 1618 and traveled widely for the next 10 years. In 1628 he settled in Holland, where he would remain until 1649. Descartes's ambition was to introduce into philosophy the rigour and clarity of mathematics. In his Meditations on First Philosophy (1641), he undertook the methodical doubt of all knowledge about which it is possible to be deceived, including knowledge based on authority, the senses, and reason, in order to arrive at something about which he can be absolutely certain; using this point as a foundation, he then sought to construct new and more secure justifications of his belief in the existence and immortality of the soul, the existence of God, and the reality of an external world. This indubitable point is expressed in the dictum Cogito ergo sum ("I think, therefore I am"). His metaphysical dualism distinguished radically between mind, the essence of which is thinking, and matter, the essence of which is extension in three dimensions. Though his metaphysics is rationalistic (see rationalism ), his physics and physiology are empiricistic (see empiricism ) and mechanistic (see mechanism ). In mathematics, he founded analytic geometry and reformed algebraic notation.