René Descartes (31 March 1596–11 February 1650) was a French philosopher, mathematician, and natural philosopher, and a major figure of the Scientific Revolution. His contributions connected algebra with geometry, proposed mechanical explanations of nature, and sought secure foundations for knowledge. His writings helped establish central questions in modern philosophy, particularly concerning certainty and the relationship between mind and body. He is commonly associated with rationalism, although observation and experiment also played roles in his scientific investigations. (mathshistory.st-andrews.ac.uk)
Life and intellectual setting
Descartes was born in La Haye, Touraine, now named Descartes. He attended the Jesuit college at La Flèche, where his studies included mathematics and the philosophy of Aristotle. In 1616 he obtained a law degree at Poitiers but did not pursue a legal career. While serving in the army of Maurice of Nassau in the Netherlands in 1618, he met Isaac Beeckman, who encouraged his investigations into mathematical problems and natural phenomena. (mathshistory.st-andrews.ac.uk)
After periods of travel and residence in France, Descartes settled in the Dutch Republic in 1628–1629 and remained there for approximately twenty years. Correspondence allowed him to participate in European intellectual networks while maintaining considerable seclusion. Marin Mersenne was an important intermediary, circulating his ideas and collecting responses. In 1649 Descartes moved to Sweden at Queen Christina’s invitation. He died in Stockholm on 11 February 1650. (plato.stanford.edu)
Principal writings
The Discourse on the Method appeared in French in 1637, accompanied by essays on optics, meteorology, and geometry. It combined intellectual autobiography with an account of disciplined reasoning. The Meditations on First Philosophy, published in Latin in 1641, developed his arguments about certainty, God, and the distinction between mind and body. It appeared with objections from contemporary thinkers and Descartes’s replies; an expanded edition followed in 1642. (plato.stanford.edu)
The Principles of Philosophy (1644) presented his metaphysics and much of his natural philosophy systematically. The Passions of the Soul (1649) examined emotions and their bodily conditions. Earlier projects, including the unfinished Rules for the Direction of the Mind and The World, appeared posthumously. Descartes withheld The World after learning of Galileo Galilei’s condemnation in 1633, because his own account likewise involved the Earth’s motion. (plato.stanford.edu)
Method, doubt, and certainty
Descartes’s method emphasized accepting only what could be recognized clearly, dividing difficult problems into manageable parts, proceeding from simpler matters to more complex ones, and reviewing reasoning for omissions. Mathematics supplied a model of orderly investigation, but his project extended beyond mathematical calculation. (plato.stanford.edu)
In epistemology, he employed systematic doubt to test the foundations of belief. The senses sometimes mislead; dreams can resemble waking experience; and an imagined powerful deceiver might undermine apparently certain judgments. These arguments used philosophical skepticism as an investigative instrument rather than as a final commitment to universal ignorance. (plato.stanford.edu)
The act of doubting nevertheless establishes that the thinker exists while thinking. This insight is conventionally expressed as cogito, ergo sum, “I think, therefore I am.” Descartes then sought to establish the existence of a non-deceiving God and the reliability of clear and distinct perceptions. Critics questioned whether this reasoning presupposed the reliability it aimed to establish—the problem known as the Cartesian circle. Its interpretation remains a subject of scholarly debate. (plato.stanford.edu)
Mind and body
In metaphysics, Descartes distinguished thinking substance from extended substance: thought characterizes mind, whereas spatial extension characterizes matter. This mind–body dualism became a central reference point in philosophy of mind. Nevertheless, he described human beings as closely united combinations of mind and body, not merely minds observing bodily machines from outside. Sensations such as hunger and pain expressed this union. (plato.stanford.edu)
His physiological explanations treated bodily processes mechanically. He assigned the pineal gland a special role in interaction between the soul and the brain, within an account involving nerves and “animal spirits,” conceived as fine material particles. These proposals belong to seventeenth-century physiology, not modern neuroscience; the gland’s alleged mediating role is not scientifically accepted. (plato.stanford.edu)
Mathematics and natural philosophy
Descartes’s La Géométrie helped establish analytic geometry by translating geometrical problems into algebraic relationships. It connected curves with equations and classified them through algebraic properties. Pierre de Fermat independently developed related techniques. Descartes’s work was foundational, but should not simply be identified with the fully standardized coordinate methods taught today. He continued to regard geometrical construction as essential rather than replacing geometry wholesale with formulas. (mathshistory.st-andrews.ac.uk)
In optics, he published the sine law of refraction and developed an explanation of the rainbow. His natural philosophy sought to explain phenomena through the size, shape, arrangement, and motion of matter. He rejected empty space and proposed that planetary motions resulted from vortices in a universe filled with matter. Although influential, this account was displaced by later physical theories. (plato.stanford.edu)
Descartes’s physics also formulated principles concerning persistence of motion and rectilinear tendencies. However, several of his collision rules were incorrect, and his conserved “quantity of motion” was not equivalent to modern vector momentum. These distinctions separate his historically influential mechanical program from the later framework of classical mechanics. (plato.stanford.edu)