René Descartes

René Descartes was born on 31 March 1596 in La Haye en Touraine, in the Province of Touraine — a town that now bears his name. His father, Joachim, held a seat in the Parlement of Rennes, placing the family among the educated professional class. In May 1597, his mother, Jeanne Brochard, died a few days after giving birth to a stillborn child. René was raised by his grandmother and great-uncle, in a region controlled by the Protestant Huguenots despite the family's Roman Catholicism.

Because of fragile health, Descartes entered the Jesuit College of La Flèche only in 1607, later than was typical. There he encountered mathematics and physics for the first time. After graduating in 1614, he spent two years at the University of Poitiers, earning a Baccalauréat and Licence in canon and civil law in 1616 — a qualification his father wanted so that he might become a lawyer. He then moved to Paris, setting aside the law for pursuits that would occupy the rest of his life.

In 1618, seeking a career as a professional military officer, Descartes joined the Protestant Dutch States Army in Breda under Maurice of Nassau as a mercenary. He undertook formal study of military engineering under the system established by Simon Stevin, and it was in Breda that he met Isaac Beeckman, principal of a Dordrecht school, who drew him into serious mathematical inquiry. For Beeckman he wrote the Compendium of Music in 1618, a treatise on music theory.

Descartes later served under the Catholic Duke Maximilian of Bavaria and was present at the Battle of the White Mountain near Prague in November 1620. According to the biographer Adrien Baillet, the decisive intellectual moment came on the night of 10 to 11 November 1619, when Descartes shut himself in a heated room in Neuburg an der Donau to escape the cold. There he experienced three vivid dreams, which he interpreted as a divine revelation pointing him toward a new philosophy grounded in mathematics. By the time he left the room, he had formulated the core ideas of analytic geometry and the ambition to apply mathematical method to all knowledge.

Descartes left the army in 1620 and eventually settled in the Dutch Republic in 1628, where he would spend more than twenty years and produce all of his major writings. He enrolled at the University of Franeker in April 1629 and subsequently at Leiden University under the name 'Poitevin,' studying mathematics with Jacobus Golius and astronomy with Martin Hortensius. In Amsterdam he had a relationship with a servant, Helena Jans van der Strom, and in 1635 their daughter Francine was born in Deventer. She died of scarlet fever at the age of five, in 1640, and Descartes wept openly — an unusual response for a moralist of the period.

The year 1633 brought a significant setback: when the Italian Inquisition condemned Galileo, Descartes abandoned plans to publish his Treatise on the World, on which he had labored for four years. He salvaged portions of the work, releasing them in 1637 as three essays — 'Les Météores,' 'La Dioptrique,' and La Géométrie — prefaced by his celebrated Discours de la méthode, the Discourse on the Method. In it he set out four rules of thought designed to ensure that knowledge rests on an unshakeable foundation. La Géométrie, developed partly in collaboration with Pierre de Fermat, established what became known as analytic geometry, linking algebra and geometry through a coordinate system that now bears Descartes's name.

In 1641 he published Meditationes de Prima Philosophia, the Meditations on First Philosophy, in Latin, followed in 1644 by Principia Philosophiae, the Principles of Philosophy, dedicated to Sophia of Hanover. His final major work, Les Passions de l'âme, The Passions of the Soul, appeared in 1649, dedicated to Princess Elisabeth of Bohemia, with whom he had maintained a long philosophical correspondence on moral and psychological subjects.

The philosophical project that made Descartes famous was rooted in a single methodological move: the deliberate rejection of anything that could be doubted, in order to discover what could not. He called this approach hyperbolic or metaphysical doubt. Rather than a scepticism for its own sake, it was a tool for excavating certainty — clearing away uncertain beliefs as a builder clears topsoil before laying foundations. From this process Descartes arrived at a single indubitable first principle: the fact that he was thinking. From that he concluded he must exist. The Latin formulation, 'cogito, ergo sum' — I think, therefore I am — first appeared in French as 'Je pense, donc je suis' in the Discourse on the Method.

Descartes's theory of mind and body, known as Cartesian dualism, held that the universe contained two fundamentally different kinds of substance: mind, defined as thinking and immaterial, and body, defined as matter and extension. He argued that these two substances were genuinely distinct because each could, in principle, exist without the other. The pineal gland, he proposed, served as the site where mind and body interacted, with animal spirits — light, fast-moving fluids in the nervous system — carrying signals between brain and muscles. This framework expelled final causes and divine purpose from the physical world, providing philosophical grounding for the new mathematical physics of Kepler and Galileo while leaving room for theological beliefs about the immortality of the soul.

By 1649 Descartes was among Europe's most celebrated philosophers and scientists. That year Queen Christina of Sweden invited him to Stockholm to help establish a new scientific academy and to tutor her in his ideas. He accepted and moved to the Swedish Empire in the middle of winter, staying at the house of the French resident Pierre Chanut on Västerlånggatan, less than five hundred meters from Castle Tre Kronor. There Chanut and Descartes used a Torricellian mercury barometer to take what Descartes considered the first barometric readings in Stockholm, exploring whether atmospheric pressure could forecast weather.

The arrangement proved uncomfortable. Christina required Descartes to tutor her three times weekly at five in the morning in her cold castle. By 15 January 1650 the two had actually met only four or five times, and it became clear they did not suit each other: she had no interest in his mechanical philosophy and he did not share her enthusiasm for ancient Greek literature. On 1 February 1650 Descartes fell ill with pneumonia. Chanut reported the cause as pneumonia, though Christina's physician Johann van Wullen identified it as peripneumonia; in any case Descartes refused van Wullen's treatment. He died on 11 February 1650.

As a Catholic in a Protestant country, Descartes was buried in the churchyard of what became Adolf Fredrik Church in Stockholm. In 1666 his remains were taken to France and interred at Saint-Étienne-du-Mont. In 1819 they were moved again, to the Abbey of Saint-Germain-des-Prés, though the reburial was incomplete — a finger and the skull were missing. An alleged skull is held at the Musée de l'Homme in Paris, though research conducted in 2020 suggests it may be a forgery.