René Descartes

René Descartes (31 March 1596 – 11 February 1650) was a French thinker who worked across many fields: philosophy (metaphysics, epistemology, ethics, philosophy of science), theology, mathematics, science (physics, optics, mechanics, cosmology, meteorology), physiology, and medicine. He is often called the father of modern philosophy because he changed how knowledge is pursued, introducing a systematic, method-based approach. Descartes rejected the authority of earlier philosophers and often stressed how his ideas differed from theirs. In the opening of *The Passions of the Soul*, he wrote as if no one had ever discussed emotions before. His most famous statement is "I think, therefore I am." He was a key figure in the Scientific Revolution, and his *Meditations on First Philosophy* and other works are still studied. In mathematics, he connected geometry and algebra to create analytic geometry, and the Cartesian coordinate system is named after him. This work helped lead to the discovery of calculus and analysis.

**Early life**

Descartes was born on 31 March 1596 in La Haye en Touraine, France. In May 1597, his mother Jeanne Brochard died a few days after giving birth to a stillborn child. His father Joachim was a member of the Parlement of Rennes. René lived with his grandmother and great-uncle. The family was Roman Catholic, but the Poitou region was controlled by Protestant Huguenots. Because of fragile health, he entered the Jesuit College of La Flèche in 1607, where he learned mathematics and physics. After graduating in 1614, he studied at the University of Poitiers for two years (1615–16), earning a Baccalauréat and Licence in canon and civil law in 1616, following his father’s wish that he become a lawyer. He then moved to Paris.

**Army service**

In 1618, aiming to become a professional military officer, Descartes joined the Protestant Dutch States Army in Breda as a mercenary under Maurice of Nassau. He formally studied military engineering as established by Simon Stevin. In Breda, he was encouraged to advance his mathematics and met Isaac Beeckman, a school principal, for whom he wrote the *Compendium of Music* (written 1618, published 1650). In 1619, serving the Catholic Duke Maximilian of Bavaria, he was present at the Battle of the White Mountain near Prague in November 1620. According to Adrien Baillet, on the night of 10–11 November 1619 (St. Martin’s Day), while in Neuburg an der Donau, Descartes shut himself in a room with a cocklestove to escape the cold. There he had three dreams and believed a divine spirit revealed a new philosophy. The second dream may have been an episode of exploding head syndrome. When he left the room, he had formulated analytic geometry and the idea of applying mathematics to philosophy. He concluded that pursuing science would be his life’s work and the path to true wisdom.

**Career**

**France:** Descartes left the army in 1620. He visited the Basilica della Santa Casa in Loreto, traveled to several countries, then returned to France and spent time in Paris. There he wrote his first essay on method, *Rules for the Direction of the Mind*. He arrived in La Haye in 1623, sold all his property, and invested in bonds, giving him a comfortable income for life. In 1627, he observed the siege of La Rochelle by Cardinal Richelieu, studying the physical properties of the great dike and mathematically analyzing everything he saw. He also met mathematician Girard Desargues. That autumn, at the residence of the papal nuncio Guidi di Bagno, he attended a lecture by an alchemist on a supposed new philosophy. Cardinal Bérulle urged him to write an exposition of his new philosophy somewhere beyond the Inquisition’s reach.

**Netherlands:** Descartes returned to the Dutch Republic in 1628. In April 1629, he joined the University of Franeker, studying under Adriaan Metius, either living with a Catholic family or renting the Sjaerdemaslot. The next year, under the name "Poitevin," he enrolled at Leiden University, a Protestant university. He studied mathematics with Jacobus Golius, who introduced him to Pappus’s hexagon theorem, and astronomy with Martin Hortensius. In October 1630, he fell out with Beeckman, accusing him of plagiarizing his ideas. In Amsterdam, he had a relationship with a servant, Helena Jans van der Strom. Their daughter Francine was born in 1635 in Deventer, baptized a Protestant, and died of scarlet fever at age five. Unlike many moralists, Descartes did not condemn the passions but defended them; he wept at Francine’s death in 1640.