René Descartes (1596-1650)René Descartes
Discourse on MethodMeditations on First Philosophy
It was probably during the first years of his residence in the Netherlands that Descartes wrote his first major work, Essais philosophiques (Philosophical Essays), published in 1637. The work contained four parts: an essay on geometry, another on optics, a third on meteors, and Discours de la méthode (Discourse on Method), which described his philosophical speculations. This was followed by other philosophical works, among them Meditationes de Prima Philosophia (Meditations on First Philosophy, 1641; revised 1642) and Principia Philosophiae (The Principles of Philosophy, 1644). The latter volume was dedicated to Princess Elizabeth Stuart of Bohemia, who lived in the Netherlands and with whom Descartes had formed a deep friendship. In 1649 Descartes was invited to the court of Queen Christina of Sweden in Stockholm to give the queen instruction in philosophy; in this year he also published the work called The Passions of the Soul. The next year, however, the rigors of the northern winter brought on the pneumonia that caused his death on February 11, 1650.
Descartes attempted to apply the rational inductive methods of science, and particularly of mathematics, to philosophy. His concern with mathematics and its power as an instrument of science profoundly influenced his philosophical system; he believed that all natural science must be capable of being unified under mathematics, and that the world must be of such a nature as to admit of mathematical treatment. Before his time, philosophy had been dominated by the method of Scholasticism, which was entirely based on comparing and contrasting the views of recognized authorities. Rejecting this method, Descartes stated, "In our search for the direct road to truth, we should busy ourselves with no object about which we cannot attain a certitude equal to that of the demonstration of arithmetic and geometry." The criterion of certainty was expressed in the rule that he would accept only those beliefs that appeared to him "clearly and distinctly" to be true, meaning propositions which anyone could see to be true by the "natural light" of reason. To test which of his previous beliefs could meet these conditions, he subjected them to a series of skeptical hypotheses (His application of this procedure of "methodical doubt" is explained principally in the Discourse on Method and in the Meditations). For example, he asked himself whether physical objects around him really existed. He reasoned that although he felt certain that at a particular moment he was seeing and feeling various physical objects, he had on many occasions felt just as certain of such things when later it had turned out that he had been dreaming, and all the things around him had been illusions. He could even doubt that he himself had a body, since his body was just another physical object among others. 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 arithmetic, such as 2 + 3 = 5, 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. "Cogito, ergo sum" ("I think, therefore I am") is thus beyond skeptical doubt. Thus he has proved his existence as a res cogitans or thinking being, as he puts it a substance whose essential attribute is that of thought.
From this Archimedean point, "I think, therefore I am," Descartes attempts to regain the world called into doubt by his skeptical hypotheses. He turns to the content of his thoughts and realizes that he has, among other ideas, the idea of a Perfect Being or God, and reasons that there must be something outside himself corresponding to this idea, that God must exist in reality and not merely in his thoughts. He is led to this conclusion first from St. Anselm's ontological argument that God is a being than which no greater can be thought and therefore can be said to exist in the mind, and that to exist actually is more perfect than to exist only in the mind; therefore God must exist in reality as well as in the mind. Descartes then argues that an idea of a perfect thing cannot be brought into being by an imperfect agent, as he is as shown by his state of doubt, which is inferior to knowledge. Hence there must really be a Perfect Being who is the origin of this idea. Since he has established the existence of God, he reasons that a Perfect Being would not allow him to be deceived about the actual existence of external objects. However, his arguments to overcome skepticism are not without their problems. One of these is known as the Cartesian circle: no argument to show that God exists can be certain unless one is certain of one's own reasoning; but, according to Descartes, one cannot be certain of one's reasoning unless one is certain that God exists. Also, as Descartes admitted, we are sometimes deceived, so how is this to be reconciled with the existence of a Perfect Being who would not deceive us? Descartes' answer at the time was that deceptions are a result of our misuse of free will. 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 body by moving a small part of the brain. Motions in that same part of the brain produce sensations and emotions. Ultimately Descartes thought that the mind or soul and body are united in a peculiar way, but the peculiar nature of this union cannot be explained. In the Passions of the Soul he suggested that the mind and body interacted through the pineal gland. This problem of whether mental entities are different in nature from physical entities continues to be a primary concern of philosophers and psychologists.
Descartes as a natural scientist argued that bodies differ from how they appear through the 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 the 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 humans, 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 the field of physiology, Descartes held that part of the blood was a subtle fluid, which he called animal spirits. The animal spirits, he believed, came into contact with thinking substances in the brain and flowed out along the channels of the nerves to animate the muscles and other parts of the body. Descartes's study of optics led him to the independent discovery of the fundamental law of reflection: that the angle of incidence is equal to the angle of reflection. His essay on optics was the first published statement of this law. Descartes's treatment of light as a type of pressure in a solid medium paved the way for the undulatory theory of light.
The most notable contribution that Descartes made to mathematics was the systematization of analytic geometry. He was the first mathematician to attempt to classify curves according to the types of equations that produce them. He also made contributions to the theory of equations. Descartes was the first to use the last letters of the alphabet to designate unknown quantities and the first letters to designate known ones. He also invented the method of indices to express the powers of numbers. In addition, he formulated the rule, which is known as Descartes's rule of signs, for finding the number of positive and negative roots for any algebraic equation.
The influence of Descartes on the history of philosophy has probably been greater than that of any other philosopher with the exception of Aristotle. He influenced the rationalists who were his immediate followers, particularly Leibniz and Spinoza, who agreed with his general account of philosophy and science. The empiricists Locke and Hume, who rejected most of his conclusions, were nevertheless profoundly affected by his approach. Descartes changed the whole course of modern philosophical enquiry by placing at the center of philosophy the epistemological question "how do I know," replacing the earlier emphasis on what the world was like with how one could know what the world was like. His philosophy contained the seeds of idealism that began with Berkeley and continued with Schelling and Hegel through the 19th century.
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1996 Grolier Multimedia Encyclopedia, Copyright 1996 Grolier Interactive, Inc.Microsoft Encarta 98 Encyclopedia, Copyright 1993-1997 Microsoft Corporation.The Concise Encyclopedia of Western Philosophy and Philosophers, J. O. Urmson and
Jonathan Rée, editors. London: Unman Hyman, 1991.