A Guide to René Descartes’ Life and Philosophy

René Descartes (1596–1650) was a seventeenth-century French philosopher, mathematician, and scientist. He helped establish multiple principles of philosophy, including modern rationalism. As a mathematician, he developed a synthesis of algebra and geometry known as analytic geometry, which is sometimes referred to as Cartesian geometry. He also invented the Cartesian coordinate system, which remains in wide use today. As a scientist, he helped develop the law of refraction (known as Descartes' Law in France) and described the angular radius of a rainbow.

During his lifetime, Descartes primarily considered himself a mathematician and a scientist. He sought to explain many natural phenomena in publications such as The World, Optics, Meteorology, Geometry, and Discourse on the Method of Rightly Conducting One's Reason and of Seeking Truth in the Sciences. He was also a Roman Catholic who used metaphysics to provide a rational explanation for the existence of God, most famously in Meditationes de prima Philosophia (Meditations on First Philosophy). Descartes rivals Aristotle for his dual contribution to metaphysical philosophy and the physical sciences.

From his childhood in France to his working life in the Netherlands to his final years in Sweden, René Descartes devoted his life to the careful study of both material things and metaphysical truths.

• Early life in France: The early years of Descartes' life were spent in France. He was born in 1596 in La Haye en Touraine, south of Paris. His mother, Jeanne Brochard, died shortly after childbirth, and his father, Joachim, was frequently away from home, tending to his duties in the Parliament of Brittany in Rennes. As such, the young Descartes was largely raised by his grandmother and great-uncle. As a boy, Descartes studied mathematics and physics (including the pioneering work of Galileo) at the Jesuit College Royal Henry-Le-Grand at La Flèche. He then went on to the University of Poitiers, graduating with degrees in canon and civil law. He moved to Paris in 1616 with the plan of becoming a lawyer or military officer.
• Military ambitions: Not long after moving to Paris, Descartes turned his focus to military service. Despite being a Catholic, he became a mercenary in the Protestant Dutch States Army in Breda, serving under Maurice of Nassau. While in Breda, Descartes took a greater interest in mathematics and engineering. There, he made the acquaintance of Dutch philosopher and mathematician Isaac Beeckman, with whom he would have a long friendship. They remained in contact until Beeckman's death in 1637.
• Religious visions: In November 1619, Descartes experienced religious visions that he claimed inspired breakthroughs in both philosophy and mathematics. He left the Protestant army and enlisted in the army of Catholic Duke Maximilian of Bavaria (present-day Germany). After some travel, Descartes returned to France, spending time in Paris and La Haye.
• A move to the Netherlands: In approximately 1628, Descartes began drafting one of his first major works, Regulae ad Directionem Ingenii (Rules for the Direction of the Mind). In 1630, he enrolled at Leiden University in the Netherlands, splitting his time between the town of Leiden and the Dutch capital of Amsterdam. An affair with a young servant named Helena Jans van der Strom produced a daughter, Francine, who died of scarlet fever not long after her fifth birthday. The loss of Francine visibly affected Descartes and may have inspired a new direction in his philosophical journey.
• Two fruitful decades: The most renowned of Descartes' works all germinated during a two-decade residency in the Netherlands. During this time, Descartes traveled extensively throughout Europe, but Holland was his home base. Early works from this era include "Les Météores" (The Meteors), "La Dioptrique" (Dioptrics), and Discours de la méthode (Discourse on the Method), which was itself an introduction to a text called La Géométrie (Geometry).
• Peak philosophical works: During the decade of the 1640s, Descartes produced his most enduring philosophical works, which would go on to upend centuries-old Aristotelian concepts and introduce a new era of natural philosophy. These works included 1641's Meditationes de Prima Philosophia (Meditations on First Philosophy), 1644's Principia Philosophiae (Principles of Philosophy), and 1649's Les Passions de l'âme (The Passions of the Soul), which Descartes dedicated to Princess Elisabeth of Bohemia.
• Final years in Sweden: In 1649, Queen Christina of Sweden proposed that Descartes chair a new scientific academy in Stockholm. Descartes accepted the position and moved to Stockholm, living as a guest at the home of Pierre Chanut. Inspired by Sweden's punishing winters, Descartes spent part of his final years testing whether atmospheric pressure could be used to predict the weather.
• Death and legacy: Descartes died of pneumonia in Stockholm on February 11, 1650. Claude Clerselier, Pierre Chanut's brother-in-law, approached the Vatican about potential sainthood for Descartes. His ambitions backfired in 1663 when the Pope placed Descartes' works on the Index of Prohibited Books. The Pope's actions were to no avail; Descartes' theories had already spread throughout Europe's intellectual community and inspired the philosophical writings of Baruch Spinoza, Gottfried Wilhelm Leibniz, François Poullain de la Barre, Nicolas Malebranche, and many future rationalists. His mathematical findings helped influence Sir Isaac Newton, who primarily studied Descartes through mathematician Frans van Schooten’s translations.

The philosophical writings of Descartes demonstrably shaped Western philosophy and provided the framework for an approach to philosophy, mathematics, and science called the Cartesian method. Several key works form the basis of Cartesianism.

1. 1. Discourse on the Method of Rightly Conducting One's Reason and of Seeking Truth in the Sciences (1637): This 1637 text introduces Descartes' most famous quote, "Je pense, donc je suis" ("I think, therefore I am"). It also provides a basis for methodological skepticism, a technique Descartes would return to in later writings. He begins with skeptical statements about various concepts that most consider to be dogmatic truisms. He then uses logic and rational arguments to establish that, indeed, these concepts and principles are true.
2. 2. Meditationes de Prima Philosophia (Meditations on First Philosophy) (1641): This relatively short publication introduced the core of Descartes' philosophy and returns to Descartes' methodological skepticism (sometimes called “Cartesian doubt”). Using both ontological arguments and trademark arguments, Descartes offers a series of proofs to assert the existence of God, humanity, and the self. The text also endures for its introduction of mind-body dualism, also called Cartesian dualism, and what became known as the mind-body problem, which future philosophers such as John Locke, Thomas Hobbes, and David Hume debated.
3. 3. Principles of Philosophy (1644): This text features the Latin quotation, "Cogito ergo sum," a translation of the French quote, "Je pense, donc je suis," and the English, "I think therefore I am." It expands on the notions of epistemology found in Descartes' Meditations, but its reputation was partially sullied by a number of statements about physics that were later disproved.
4. 4. Les Passions de l'âme (The Passions of the Soul) (1649): This work marked Descartes' final philosophical treatise. The text explores the relationship between science and moral philosophy. It also revisits the mind-body dualism (Cartesian dualism) introduced in prior works and presents the concept of "animal spirits," which Descartes believed to control physiological behavior within human beings. He declared that passions attack the soul and compel the body to behave with impropriety. The text submits that understanding passions, and controlling them, is integral to a moral life.

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