The French philosopher Rene Descartes, b. Mar. 31, 1596, d. Feb. 11, 1650, was one of the most important and influential thinkers in human history and is sometimes called the founder of modern philosophy. Writing at the beginning of the scientific revolution, he made major contributions to both philosophy and mathematics.
His principal philosophical work, Meditations on First Philosophy, was first published in 1641, the year before Galileo died and Isaac Newton was born. One of his two main aims in philosophy was to provide a conceptual foundation for the new mechanical physics based on the Copernican system, which tried to explain everything in the created world external to human beings solely by the shapes, sizes, and motions of bodies. Because he lived at a time when traditional ideas were being questioned, he also sought to devise a method for reaching the truth.
This concern and his method of systematic doubt had an enormous impact on the subsequent development of philosophy. Life and Works Born in Touraine, France, Descartes was educated at the Jesuit academy of La Fleche in traditional Aristotelian philosophy. After receiving a law degree in 1616 at the University of Poitiers, he traveled through Europe as a volunteer in a Dutch and then a Bavarian army.
In his early twenties he began working on problems in mathematics and mechanics under the influence of the Dutch scientist Isaac Beeckman, and he first conceived of developing a unified science of nature. In late 1628, as the result of a speech in Paris in which he argued that the sciences must be founded on certainty, he was encouraged by Cardinal Pierre de Berulle (1575-1629) to develop his own philosophical system. Shortly afterward, he settled in Holland, which offered him seclusion and more intellectual freedom, and began work on his first major treatise, Rules for the Direction of the Mind.
This work was never completed and was published posthumously in 1701. Upon hearing of Galileo’s condemnation by the Inquisition in 1633 for defending the Copernican system, Descartes suppressed publication of his own work The World, in which he had taken the same position.
His three most important philosophical works, the Discourse on Method—which was a preface to his Dioptrics, Meteors and Geometry—the Meditations on First Philosophy, and the Principles of Philosophy, were all published in the period from 1637 to 1644.
Also important are The Passions of the Soul, Notes Against a Program, and his large correspondence. In 1649, Descartes was persuaded by Queen Christina of Sweden to leave Holland for Stockholm, where, after only a few months, he caught pneumonia and died. Cartesian Philosophy Descartes adopted the strategy of withholding his belief from anything that was not entirely certain and indubitable.
To test which of his previous beliefs could meet these conditions, he subjected them to a series of skeptical hypotheses. For example, he asked himself whether he could be certain he was not dreaming. His most powerful skeptical hypothesis, that there is an evil genius trying to deceive him, challenges not only the belief that the physical world exists, but also belief in simple statements of fact, and thus would seem to call into question the validity of reason itself. But not even an evil genius could deceive someone into believing falsely that he existed. "I think, therefore I am" is thus beyond skeptical doubt.
From this Archimedean point, "I think, therefore I am," Descartes attempted to regain the world called into doubt by his skeptical hypotheses. His solution to the problem was rejected by later generations, however, and philosophers have been struggling with skepticism—especially skepticism about the existence of the physical world ever since. Descartes is known as the father of the mind-body problem.
He claimed that human beings are composites of two kinds of substances, mind and body. A mind is a conscious or thinking being, that is, it understands, wills, senses, and imagines. A body is a being extended in length, width, and breadth. Minds are indivisible, whereas bodies are infinitely divisible. The "I" of the "I think, therefore I am" is the mind and can exist without being extended, so that it can in principle survive the death of the body. Despite having different natures, Descartes thought that mind and body causally interact.
The human mind causes motions in the bodies by moving a small part of the brain. Motions in that same part of the brain produce sensations and emotions. This problem of whether mental entities are different in nature from physical entities continues to be a primary concern of philosophers and psychologists.
Descartes argued that bodies differ from how they appear through senses. Colors, sounds, tastes, smells, heat, and cold are merely sensations existing in thought, and there is nothing in bodies that resembles them, just as there is nothing in bodies that resembles our sensation of pain. Instead the properties of bodies are those which are capable of being quantified, namely, extension and its modes, shape, size, and motion. He denied the existence of a vacuum, because what one would be inclined to call empty space meets his definition of body in virtue of being extended in three dimensions.
All the phenomena in the created world external to human beings, such as gravity, magnetism, and the cohesion of bodies, as well as the complex functioning of living organisms including human bodies, he believed could be explained solely by mechanistic physics, that is, by the motions and collisions of bodies.
He even denied that consciousness must be attributed to animals in order to explain their behavior. Although his laws of impact, his vortex theory of gravity, and his denial of a vacuum were rejected as physics developed, he deserves credit for one of the first formulations of the law of inertia, which he justified by appeal to the immutability of God.
In mathematics Descartes is famous for the unification of algebra and geometry, marked by the use of what are now known as Cartesian coordinates. He influenced not only the rationalist thinkers who were his immediate followers, but also the whole course of modern philosophical enquiry, and the Cartesian quest for certainty gave epistemology the central place in philosophical thought it has maintained to this day.
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