René Descartes

• 1. Introduction

  ›

  René Descartes opened his treatise on emotions, the Passions of the Soul, with a startling promise. He would write on the topic, he said, "as if no one had written on these matters before." That refusal to bow to earlier authorities runs through everything he did. Born in France in 1596, he was a philosopher, scientist, logician, and mathematician who set his views deliberately apart from the thinkers who came before him. His best-known line, "cogito, ergo sum," still echoes: "I think, therefore I am."

  He is often called the father of modern philosophy. He is also credited as the father of analytic geometry. The Cartesian coordinate system carries his name. But how does one man come to reshape both how we reason about the mind and how we draw a curve on a grid? The answer begins on a cold night in 1619, in a room with a stove, where Descartes had three dreams. It runs through army camps, Dutch inns, and a freezing castle in Stockholm where it ended. Along the way are a lost child, a forged skull, and a quarrel with a queen over the hour of 5 a.m.

• 2. Three Dreams And A Stove

  ›

  On the night of the 10th to the 11th of November 1619, St. Martin's Day, Descartes shut himself in a room with an "oven," probably a cocklestove, to escape the cold. He was stationed in Neuburg an der Donau. While inside, he had three dreams and believed a divine spirit had revealed to him a new philosophy. The second dream, according to later accounts, may have been an episode of exploding head syndrome, in which a loud noise is imagined.

  Adrien Baillet is the source for this story. By the time Descartes left the room, he had formulated analytic geometry and the idea of applying the mathematical method to philosophy. He concluded from these dreams that the pursuit of science would be, for him, the pursuit of true wisdom and a central part of his life's work.

  The path to that room ran through soldiering, not scholarship. In 1618, in pursuit of becoming a professional military officer, Descartes joined the Protestant Dutch States Army at Breda as a mercenary, under Maurice of Nassau. He studied military engineering as established by Simon Stevin. From 1619 he served the Catholic Duke Maximilian of Bavaria, and in November 1620 he was present at the Battle of the White Mountain near Prague. The soldier who fought on both Protestant and Catholic sides would soon be courted by cardinals.

• 3. The Marketplace Encounter

  ›

  It is said that Descartes and Isaac Beeckman met while both stood looking at a placard set up in the Breda marketplace, detailing a mathematical problem to be solved. Descartes asked Beeckman to translate the problem from Dutch to French. Beeckman was the principal of a Dordrecht school and an amateur scientist at the forefront of a new school of thought known as mechanical philosophy.

  Beeckman drew Descartes toward a corpuscularian approach to mechanical theory and convinced him to devote his studies to a mathematical approach to nature. In 1628, Beeckman introduced him to many of Galileo's ideas. Together they worked on free fall, catenaries, conic sections, and fluid statics. Both believed it was necessary to create a method that thoroughly linked mathematics and physics.

  For Beeckman, Descartes wrote the Compendium of Music, composed in 1618. The friendship did not last. In October 1630 the two had a falling-out, with Descartes accusing Beeckman of plagiarizing some of his ideas. The man who taught him to fuse mathematics and physics became, for a time, an enemy.

• 4. Twenty Years In Holland

  ›

  Descartes wrote all of his major work during his 20-plus years in the Netherlands, despite frequent moves. In April 1629 he joined the University of Franeker, studying under Adriaan Metius. The next year, under the name "Poitevin," he enrolled at Leiden University, then a Protestant institution. There he studied mathematics with Jacobus Golius, who confronted him with Pappus's hexagon theorem, and astronomy with Martin Hortensius.

  In Amsterdam he had a relationship with a servant girl, Helena Jans van der Strom. Their daughter, Francine, was born in 1635 in Deventer and baptized a Protestant. She died of scarlet fever at the age of 5. Unlike many moralists of the time, Descartes did not deprecate the passions but defended them. He wept upon Francine's death in 1640. According to a 2018 biography by Jason Porterfield, "Descartes said that he did not believe that one must refrain from tears to prove oneself a man." Russell Shorto speculates that fatherhood and the loss of a child marked a turning point, shifting his work from medicine toward a quest for universal answers.

  In 1633, Galileo was condemned by the Italian Inquisition, and Descartes abandoned plans to publish his Treatise on the World. He had spent the previous four years on it. In 1637 he published parts of it as three essays, "Les Météores," "La Dioptrique," and La Géométrie, preceded by his famous Discours de la méthode. In 1643, Cartesian philosophy was condemned at the University of Utrecht, and he was obliged to flee, ultimately settling in Egmond-Binnen. The Latin Meditationes de Prima Philosophia followed in 1641, and the Principia Philosophiae in 1644.

• 5. Doubt As Foundation

  ›

  "Cogito, ergo sum." In the Discourse on the Method, Descartes arrives first at a single principle: he thinks. He reasoned that if he doubted, then something or someone must be doing the doubting, and so the very act of doubting proved his existence. The phrase began in French, "Je pense, donc je suis."

  To reach that bedrock, Descartes employed what he called hyperbolic or metaphysical doubt, also known as Cartesian doubt. He rejected any idea that could be doubted, then re-established what survived, building a firm foundation for genuine knowledge. He compared the work to architecture. The top soil is taken away to make room for a new structure. His doubt was the soil; new knowledge was the buildings.

  Descartes defined "thought" as "what happens in me such that I am immediately conscious of it." He decided that perceiving his body through the senses gave unreliable evidence, so the only indubitable knowledge was that he is a thinking thing. He gave reasons that waking thoughts can be distinguished from dreams. He argued the mind cannot have been hijacked by an evil demon placing an illusory world before the senses. Discarding perception, he admitted only deduction as a method, and on that narrow ground he proposed to rebuild a whole system of knowledge.

• 6. Mind, Body, And Animal Spirits

  ›

  At the Château de Saint-Germain-en-Laye near Paris, automatons were on display, and they shaped Descartes's thinking about how mind and body interact. From this came his signature doctrine, Cartesian dualism. The universe, he held, contained two radically different kinds of substance: the mind or soul, defined as thinking, and the body, defined as unthinking matter. Two substances are really distinct, he argued, when each can exist apart from the other.

  "I am not merely present in my body as a pilot in his ship," he wrote, but "very closely joined and, as it were, intermingled with it." If it were otherwise, he reasoned, he would not feel pain when the body was hurt but would notice the damage purely by the intellect, as a sailor sees if something in his ship is broken. The mind, he insisted, is utterly indivisible, while the body is an extended thing. He gave priority to the mind and argued it could exist without the body, though the body could not exist without the mind.

  In The Passions of the Soul, published in 1649, Descartes took up the common belief in animal spirits, light fluids circulating rapidly through the nervous system between brain and muscles. He distinguished six basic passions: wonder, love, hatred, desire, joy, and sadness. He singled out the pineal gland as the connector between soul and body, with signals passing to it from the ear and eye. He also described automatic bodily reactions, like a hand pulling away from a fire, that require no thought process. This work would later influence 19th-century reflex theory.

  On animals, Descartes argued they did not lack sensations or perceptions, but that these could be explained mechanistically, without any soul. Because animals had no soul, he held, they could not feel pain or anxiety; signs of distress merely protected the body from damage. His view allowed humans to treat animals with impunity, sanctioned in law and societal norms until the middle of the 19th century. The publications of Charles Darwin would eventually erode it, arguing that continuity between humans and other species suggested the possibility of animal suffering.

• 7. Algebra Meets Geometry

  ›

  Descartes invented the convention of representing unknowns in equations by x, y, and z, and knowns by a, b, and c. He pioneered the standard notation that uses superscripts to show powers, the 2 in x squared. These small choices still sit in every algebra textbook.

  Together with Pierre de Fermat, Descartes developed Cartesian or analytic geometry, which uses algebra to describe geometry. Both men drew on the Ancient Greek mathematicians Pappus of Alexandria and Apollonius of Perga, and on the symbolic algebra of François Viète. The step their predecessors failed to take was using coordinates to study the relationship between geometry and algebra. European mathematicians had treated geometry as the more fundamental form, the foundation of algebra. Equations of degree higher than the third were regarded as unreal, since a cube occupied the largest dimension of reality. Descartes professed that the abstract quantity a squared could represent length as well as area, against Viète's insistence that a second power must represent an area.

  Descartes's influence reached the young Isaac Newton, but not directly from the French La Géométrie. It came through Frans van Schooten's expanded second Latin edition. Newton continued Descartes's work on cubic equations, freeing the subject from Greek perspectives. The work also provided the basis for the calculus developed by Leibniz and Newton, who applied infinitesimal calculus to the tangent line problem. His rule of signs remains a common method for finding the number of positive and negative roots of a polynomial.

• 8. The Queen And The Cold

  ›

  By 1649, Descartes had become one of Europe's most famous philosophers and scientists. Queen Christina of Sweden invited him to her court to organize a new scientific academy and to tutor her in his ideas about love. He accepted and moved to the Swedish Empire in the middle of winter. He stayed at the house of Pierre Chanut on Västerlånggatan, less than 500 meters from Castle Tre Kronor in Stockholm. There, challenging Blaise Pascal, he took the first set of barometric readings in Stockholm, testing whether atmospheric pressure could forecast the weather.

  Descartes arranged to tutor Christina three times weekly at 5 a.m. in her cold and draughty castle. By the 15th of January 1650, the queen had met with him only four or five times. They did not like each other. She did not care for his mechanical philosophy, and he did not share her interest in Ancient Greek language and literature. On the 1st of February 1650 he contracted pneumonia, and he died on the 11th of February at Chanut's. His reported last words: "My soul, though has long been held captive. The hour has now come for thee to quit thy prison."

  The afterlife of his body was as restless as his life. A Catholic in a Protestant nation, he was first interred in a churchyard where mainly orphans were buried, the future Adolf Fredrik Church. In 1663 the Pope placed his works on the Index of Prohibited Books, and in 1671 Louis XIV prohibited all lectures in Cartesianism. In 1666 his remains were taken to France and buried in Saint-Étienne-du-Mont. He was reburied again in 1819 in the Abbey of Saint-Germain-des-Prés, missing a finger and the skull. The skull in the Musée de l'Homme in Paris may be a forgery, while one fragment of the original reached the University of Lund in 1691, where it is still preserved.

  Descartes's deeper inheritance was not his skull but a shift in who guarantees truth. By moving the debate from "what is true" to "of what can I be certain," he raised the human being to a subject equipped with autonomous reason. That anthropocentric turn, Martin Heidegger argued, provided the basis for all subsequent anthropology. The Discourse first appeared in a single edition of 500 copies, 200 set aside for the author, a slim beginning for a book that helped set the agenda for the modern age.