René Descartes

René Descartes was a metaphysician, mathematician, and natural philosopher responsible for changing the course of philosophy and creating analytic geometry and an influential physical theory. His early life is obscure.

Born into a wealthy French family of physicians and civil servants, he was educated at the Jesuit College of La Flèche from 1606 to 1614, taking a law degree from the University of Poitiers in 1616. He then wandered through Europe as a soldier. He later claimed that in 1619, in Germany, he had a vision of a new philosophy. Descartes envisioned himself as a new Aristotle, with a philosophy universal in its application.

In 1628, Descartes settled in the Dutch Republic, remaining there for 20 years. Descartes was a loyal Catholic who, despite living in a Protestant society, never showed any interest in conversion. He differed from Catholic orthodoxy in his acceptance of the Sun-centered Copernican astronomy.

Although Descartes was in no physical danger from the church, he was shocked by his fellow Copernican Galileo Galilei’s condemnation in 1633. Abandoning a treatise on the verge of publication that would have systematically expounded his natural philosophy, Descartes turned to metaphysics to find a religiously unimpeachable basis for natural knowledge.

In 1638, he published Discourse on Method, setting forth his program for natural philosophy and three associated treatises he claimed exemplified his method on geometry, optics, and meteorology, including matter theory.

These works were in French rather than Latin, aimed at an educated public, rather than university scholars. Descartes was the first notable European male intellectual to think of women as an important part of his audience.

The Discourse sets forth the famous cogito ergo sum (although not in those words), Descartes’s argument that the very process of thinking proves that the thinker exists. This metaphysics was further elaborated in Meditations on First Philosophy, published with a number of objections from others and replies by Descartes in 1641.

statue of Rene Descartes
statue of Rene Descartes

Descartes attempted to use the cogito as a foundation for both metaphysical claims (a logical proof of the existence of God) and physical ones—that which can be logically deduced from known truths can be certain. Descartes’s proof of the existence of God is similar to the famous “ontological argument” of Anselm of Canterbury.

God’s perfection is so great that our “clear and distinct” idea of it could not have been caused by a being less perfect than God. Indeed, the clearness with which we hold the idea of God is in itself proof of God’s existence. Descartes was a rationalist who viewed logical consistency as prior to empirical observation.

As a natural philosopher, Descartes set forth a vision of nature as mechanical, a “mechanical philosophy.” He did so most systematically in his 1644 Latin textbook, Principles of Philosophy.

He claimed that the universe was full of matter, defined as that which occupied space—Descartes, like Aristotle, denied the possibility of a vacuum—and everything that occurred in the material universe could be explained by the interaction of matter and motion. Descartes’s picture of matter in motion was dominated by vortices, whirlpools of matter.

Large vortices carried the planets around the Sun while smaller ones on Earth explained various physical phenomena such as the weather and magnetism. This led to the problem of the interaction of the human soul, whose spiritual nature Descartes accepted, with the material and mechanical human body. He suggested that this interaction might the function of the pineal gland.

Descartes was a great mathematician, and along with his contemporary and rival Pierre de Fermat, he founded analytic geometry. Descartes used these powerful methods to solve long-standing matimatical problems.

He also introduced the still-existing convention of representing powers by numerical superscripts, an important contribution toward making mathematics more abstract, as the previous convention of referring to second powers as squares and third powers as cubes made it hard to deal with fourth and higher powers. In optics, Descartes independently rediscovered the sine law of refraction previously known to the English scientist Thomas Harriot and the Dutch professor Willebrod Snell, now known as Snell’s law.

By the 1640s, Descartes ran into trouble in the Dutch Republic where Cartesianism had won an extensive and vociferous following. Intellectually conservative, university-based Aristotelian Calvinists identified Cartesianism with their liberal Protestant enemies.

Although Descartes was not a courtier by nature and was quite concerned in his career to avoid patronage, he eventually succumbed to the lure of the court, and went to Stockholm in 1649 to tutor the brilliant young Queen Christina Vasa of Sweden (1626–89) in philosophy.

Unfortunately, she wanted to be tutored at 5 a.m. during one of the coldest winters in Swedish history, and Descartes died shortly thereafter. His last work to be published in his lifetime was The Passions of the Soul. It sets forth Descartes’s theories of the relation of the soul and body and recommends the government of the passions lest they lead people into evil deeds.

Descartes’s body was returned to France in 1667. As further developed by other philosophers, Cartesianism became the dominant school of philosophy in France and widely influential elsewhere.