1596–1650 · La Haye en Touraine, France
"Cogito, ergo sum."
— I think, therefore I am. Discourse on the Method (1637)René Descartes was a French philosopher, mathematician, and scientist who is often called the father of modern philosophy. Born into a family of minor nobility in La Haye en Touraine (now Descartes, Indre-et-Loire), he was educated at the Jesuit College of La Flèche and the University of Poitiers. Dissatisfied with the scholastic tradition, he sought to rebuild knowledge on foundations of absolute certainty. His work bridged the medieval and modern worlds, introducing a rigorous method of doubt, a new metaphysics of mind and body, and innovations in mathematics and physics that would shape the Scientific Revolution.
Born in La Haye en Touraine; mother died in infancy; raised by grandmother and great-uncle.
Educated at the Jesuit College Royal Henry-Le-Grand at La Flèche; studied classics, logic, mathematics, and Aristotelian philosophy.
Earned law degree from the University of Poitiers; never practiced, preferring to travel and study.
Joined the Dutch States Army; met Isaac Beeckman, who rekindled his interest in mathematics and physics.
Three dreams on the night of November 10–11 convinced him his mission was to found a unified science; began developing his method.
Moved to the Dutch Republic, where he would live for most of his adult life, valuing its intellectual freedom.
Published Discourse on the Method with three scientific essays (Dioptrics, Meteors, Geometry); introduced analytic geometry and the cogito.
Published Meditations on First Philosophy, his central metaphysical work; defended against objections from Hobbes, Gassendi, Arnauld, and others.
Published Principles of Philosophy, a comprehensive system of physics and metaphysics intended for use in schools.
Accepted invitation from Queen Christina of Sweden to tutor her in philosophy; moved to Stockholm.
Died in Stockholm, likely of pneumonia, at age 53; buried in Sweden, later reinterred in Paris.
Even if an evil demon deceives me about everything, the fact that I am deceived—that I think—proves I exist. The act of doubting presupposes a doubter. This becomes the first indubitable truth from which Descartes rebuilds knowledge.
Methodological skepticism: reject as false any belief that can be doubted, even slightly. Sense experience, mathematics, and logic are all subject to doubt until proven otherwise. Only what survives this test qualifies as certain knowledge.
The mind (res cogitans) and body (res extensa) are distinct substances. The mind is unextended, indivisible, and thinks; the body is extended, divisible, and occupies space. Their interaction remains a notorious philosophical puzzle.
Four rules for right reasoning: accept only what is clear and distinct; divide difficulties into simpler parts; proceed from the simple to the complex; enumerate and review so nothing is omitted. Modeled on mathematics.
Truth criterion: whatever I perceive clearly and distinctly is true. Clarity means present and manifest to the attentive mind; distinctness means so sharply separated from other ideas that it contains nothing unclear.
A thought experiment: suppose an omnipotent demon deceives me about everything—the external world, mathematics, even my own body. What could I still know? Used to radicalize doubt before the cogito provides an anchor.
Descartes made lasting contributions to mathematics, most notably the development of the Cartesian coordinate system. In his Geometry (1637), he showed how to represent geometric figures algebraically and algebraic equations geometrically by assigning numerical coordinates to points on a plane. This fusion of algebra and geometry—analytic geometry—unified curves and equations, enabled the study of functions, and laid the groundwork for calculus. The familiar x–y axes, though refined by later mathematicians, bear his name. He also introduced the convention of using letters at the end of the alphabet (x, y, z) for unknowns and the beginning (a, b, c) for knowns, notation still in use today.
Descartes' influence on modern philosophy is profound. His demand for certainty and his method of doubt set the agenda for epistemology for centuries. The mind-body problem he posed remains central to philosophy of mind. His mechanistic view of the physical world—bodies as extended matter governed by laws—advanced the Scientific Revolution and influenced Newton. His rationalism, emphasis on the individual thinking subject, and proof of God's existence from the idea of perfection shaped Spinoza, Leibniz, and the Enlightenment. Critics from the empiricists (Locke, Hume) to phenomenologists (Husserl, Heidegger) have defined themselves against his legacy. In mathematics, analytic geometry is foundational. He is, in short, one of the architects of the modern intellectual world.
"It is not enough to have a good mind; the main thing is to use it well."
— Discourse on the Method