Descartes, René (1596-1650)

Cartesian dualism, the idea that the universe is made up of matter and of mind, was a philosophy put forward by the French philosopher and mathematician René Descartes (1596-1650), seen here in a portrait by the Dutch painter Frans Hals. The philosopher was frequently attacked by the Catholic Church for his beliefs, and spent the later years of his life in the Protestant Netherlands.

A portrait of René Descartes. Most popularly famous for the statement ‘cogito ergo sum’ (I think, therefore I am), he is considered by many to be the founder of modern philosophy.

French philosopher and mathematician. He believed that commonly accepted knowledge was doubtful because of the subjective nature of the senses, and attempted to rebuild human knowledge using as his foundation the dictum cogito ergo sum (‘I think, therefore I am’). He also believed that the entire material universe could be explained in terms of mathematical physics, and founded coordinate geometry as a way of defining and manipulating geometrical shapes by means of algebraic expressions. Cartesian coordinates, the means by which points are represented in this system, are named after him. Descartes also established the science of optics, and helped to shape contemporary theories of astronomy and animal behaviour.

Descartes identified the ‘thinking thing’ (res cogitans), or mind, with the human soul or consciousness; the body, though somehow interacting with the soul, was a physical machine, secondary to, and in principle separable from, the soul. He held that everything has a cause; nothing can result from nothing. He believed that, although all matter is in motion, matter does not move of its own accord; the initial impulse comes from God. He also postulated two quite distinct substances: spatial substance, or matter, and thinking substance, or mind. This is called ‘Cartesian dualism’, and it preserved him from serious controversy with the church.

Descartes was born in La Haye (renamed Descartes in his honour), south of Tours, and studied at Poitiers. He served in the army of Prince Maurice of Orange, and in 1619, while travelling through Europe, decided to apply the methods of mathematics to metaphysics and science. He settled in the Netherlands 1628, where he was more likely to be free from interference by the Catholic Church. In 1649 he visited the court of Queen Christina of Sweden, and shortly thereafter he died in Stockholm.

Descartes's great work in mathematics was La Géométrie/Geometry 1637. Although not the first to apply algebra to geometry, he was the first to apply geometry to algebra. He was also the first to classify curves systematically, separating ‘geometric curves’ (which can be precisely expressed as an equation) from ‘mechanical curves’ (which cannot). Other works include Discourse on Method 1637, Meditations on the First Philosophy 1641, and Principles of Philosophy 1644, and numerous books on physiology, optics, and geometry.