René Descartes
1596–1650, La Haye en Touraine (now Descartes), France, Stockholm, Sweden
French philosopher and mathematician whose La Géométrie (1637) fused algebra and geometry by representing curves as equations in coordinates, founding what is now called analytic or Cartesian geometry and supplying the notation (x, y, exponents) still used in algebra today.
René Descartes was born on 31 March 1596 in La Haye en Touraine, France — later renamed Descartes in his honor — the son of Joachim Descartes, a member of the parliament of Brittany. His mother died when he was an infant, and he was raised largely by his grandmother; frail health as a child earned him permission to spend mornings in bed, a habit of prolonged reflection he kept for life. From about 1604 he studied at the Jesuit college of La Flèche, receiving a thorough grounding in classics, Aristotelian philosophy and mathematics.
After completing legal studies, Descartes spent roughly a decade travelling across Europe, in part through periods of military service that gave him occasion to observe different societies. In 1619, while stationed near the Danube, he experienced a set of vivid dreams that he later described as convincing him that a unified science could be built on a foundation of clear mathematical reasoning. Around 1628 he settled in the Dutch Republic, whose relative intellectual freedom suited his work, and lived in several Dutch cities over the following two decades while developing his philosophical and scientific system.
Descartes' major mathematical work, La Géométrie, appeared in 1637 as an appendix to his philosophical Discourse on the Method. Before Descartes, geometry and algebra were largely separate disciplines; La Géométrie showed how a curve could be represented by an algebraic equation in coordinates and, conversely, how algebraic equations could be studied through the curves they define — the coordinate approach now called analytic or Cartesian geometry, which became indispensable groundwork for the calculus that Newton and Leibniz would develop later in the century. Descartes also introduced much of the algebraic notation still used today, including letters from the start of the alphabet (a, b, c) for known quantities, letters from the end (x, y, z) for unknowns, and superscripts for powers.
Descartes is equally significant as a philosopher, for his method of systematic doubt, summarized in the phrase 'I think, therefore I am,' and for his dualist separation of mind and body. In 1649 he accepted an invitation from Queen Christina of Sweden to tutor her in Stockholm; the harsh climate and the queen's insistence on early-morning lessons undermined his health, and he died of pneumonia on 11 February 1650 in Stockholm. His remains were later returned to France.
Workplaces: Dutch Republic (Amsterdam, Utrecht, Leiden and other cities), Royal court of Queen Christina, Stockholm
France