René Descartes was born in 1596 in a town now named for him

René Descartes was born on 31 March 1596 in his maternal grandmother’s house in La Haye, in the Touraine region of France, about 47 km south of Tours. The town has since been renamed Descartes in his honour.

His start was precarious. His mother, Jeanne Brochard, died in childbirth when he was about 13½ months old, and he spent his early years with his grandmother in La Haye while his father, a lawyer, was often away at the Parliament of Brittany in Rennes.

He grew into the thinker often credited with founding modern philosophy and, through La Géométrie (1637), with applying algebra to geometry: the x–y Cartesian coordinates on every school graph carry his name.

The phrase he didn’t quite write

Descartes is best known for “cogito, ergo sum”: “I think, therefore I am.” Yet that canonical formula does not expressly appear in his Meditations (1641), the book most people link it to. There, after imagining that a deceiver might be fooling him about everything, he concludes that the proposition “I am, I exist” is necessarily true whenever he puts it forward or conceives it. The tidy “therefore” version is a summary; in his Principles of Philosophy he called the cogito the first and most certain truth for anyone who philosophises in an orderly way.

Some of his science aged less well. His idea that the planets are carried around the Sun by a vast vortex of invisible matter stayed popular even after Newton proposed universal gravitation in 1687, but had largely faded by 1750.

He died in Stockholm on 11 February 1650. Queen Christina of Sweden had persuaded him to come north and wanted her sessions at 5 a.m.; Descartes, who had always slept until 11, walked to the palace through the northern winter and died of pneumonia within a few months.