The French thinker René Descartes (1596-1650) is called the father of modern philosophy. He initiated the movement generally termed rationalism, and his Discourse on Method and Meditations defined the basic problems of philosophy for at least a century.

To appreciate the novelty of the thought of René Descartes, one must understand what modern philosophy, or rationalism, means in contrast to medieval, or scholastic, philosophy. The great European thinkers of the 9th to 14th century were not incapable of logical reasoning, but they differed in philosophic interests and aims from the rationalists. Just as the moderns, from Descartes on, usually identified philosophy with the natural and pure sciences, so the medievals made little distinction between philosophical and theological concerns.

The medieval doctors, like St. Thomas Aquinas, wanted to demonstrate that the revelations of faith and the dictates of reason were not incompatible. Their universe was that outlined by Aristotle in his Physics--a universe in which everything was ordered and classified according to the end that it served. During the Renaissance, however, men began exploring scientific alternatives to Aristotle's hierarchical universe. Further, new instruments, especially Galileo's telescope, added precision to scientific generalizations.

By the beginning of the 17th century the medieval tradition had lost its creative impetus. But the schoolmen, so called because they dominated the European universities, continued to adhere dogmatically to the traditional philosophy because of its association with Catholic theology. The rationalists, however, persistently refused professorships in order to preserve their intellectual integrity or to avoid persecution. They rejected the medieval practice of composing commentaries on standard works in favor of writing original, usually anonymous, treatises on topics suggested by their own scientific or speculative interests. Thus the contrast is between a moribund tradition of professorial disputes over trivialities and a new philosophy inspired by original, scientific research.

Descartes participated in this conflict between the scholastic and rationalist approaches. He spent a great part of his intellectual effort--even to the extent of suppressing some of his writings--attempting to convince ecclesiastical authorities of the compatibility of the new science with theology and of its superiority as a foundation for philosophy.

Early Life

Descartes was born on March 31, 1596, in La Haye, in the Touraine region, between the cities of Tours and Poitiers. His father, Joachim, a member of the minor nobility, served in the Parliament of Brittany. Jeanne Brochard Descartes, his mother, died in May 1597. Although his father remarried, Descartes and his older brother and sister were raised by their maternal grandmother and by a nurse for whom he retained a deep affection.

In 1606 Descartes entered La Flèche, a Jesuit college established by the king for the instruction of the young nobility. In the Discourse Descartes tells of the 8-year course of studies at La Flèche, which he considered "one of the most celebrated schools in Europe." According to his account, which is one of the best contemporary descriptions of 17th-century education, his studies left him feeling embarrassed at the extent of his own ignorance.

The young Descartes came to feel that languages, literature, and history relate only fables which incline man to imaginative exaggerations. Poetry and eloquence persuade man, but they do not tell the truth. Mathematics does grasp the truth, but the certainty and evidence of its reasoning seemed to Descartes to have only practical applications. Upon examination, the revelations of religion and morals seem as mysterious to the learned as to the ignorant. Philosophy had been studied by the best minds throughout the centuries, and yet "no single thing is to be found in it which is not subject to dispute." Descartes says that he came to suspect that even science, which depends upon philosophy for its principles, "could have built nothing solid on foundations so far from firm."

Travel and First Writings

The 18-year-old Descartes left college with a reputation for extreme brilliance. In the next years he rounded out the education befitting a young noble. He learned fencing, horsemanship, and dancing and took a law degree from Poitiers.

From 1618 to 1628 Descartes traveled extensively throughout Europe while attached to various military units. Although a devout Catholic, he served in the army of the Protestant prince Maurice of Nassau but later enlisted in the Catholic army of Maximilian I of Bavaria. Living on income from inherited properties, Descartes served without pay and seems to have seen little action; he was present, however, at the Battle of Prague, one of the major engagements of the Thirty Years War. Descartes was reticent about this period of his life, saying only that he left the study of letters in order to travel in "the great book of the world."

This period of travel was not without intellectual effort. Descartes sought out eminent mathematicians, scientists, and philosophers wherever he traveled. The most significant of these friendships was with Isaac Beeckman, the Dutch mathematician, at whose suggestion Descartes began writing scientific treatises on mathematics and music. He perfected a means of describing geometrical figures in algebraic formulas, a process that served as the foundation for his invention of analytic geometry. He became increasingly impressed with the extent to which material reality could be understood mathematically.

During this period Descartes was profoundly influenced by three dreams which he had on Nov. 10, 1619, in Ulm, Germany. He interpreted their symbols as a divine sign that all science is one and that its mastery is universal wisdom. This notion of the unity of all science was a revolutionary concept which contradicted the Aristotelian notion that the sciences were distinguished by their different objects of study. Descartes did not deny the multiplicity of objects, but rather he emphasized that only one mind could know all these diverse things. He felt that if one could generalize man's correct method of knowing, then one would be able to know everything. Descartes devoted the majority of his effort and work to proving that he had, in fact, discovered this correct method of reasoning.

From 1626 to 1629 Descartes resided mainly in Paris. He acquired a wide and notable set of friends but soon felt that the pressures of social life kept him from his work. He then moved to Holland, where he lived, primarily near Amsterdam, for the next 20 years. Descartes cherished the solitude of his life in Holland, and he described himself to a friend as awakening happily after 10 hours of sleep with the memory of charming dreams. He said his life in Holland was peaceful because he was "the only man not engaged in merchandise." There Descartes studied and wrote. He carried on an enormous correspondence throughout Europe, and in Holland he acquired a small, but dedicated, set of friends and disciples. Although he never married, Descartes fathered a natural daughter who was baptized Francine. She died in 1640, when she was 5.

First Works

Descartes's research in mathematics and physics led him to see the need for a new methodology, or way of thinking. His first major work, Rules for the Direction of the Mind, was written by 1629. Although circulated widely in manuscript form, this incomplete treatise was not published until 1701. The work begins with the assumption that man's knowledge has been limited by the erroneous belief that science is determined by the various objects of experience. The first rule therefore states that all true judgment depends on reason alone for its validity. For example, the truths of mathematics are valid independently of observation and experiment. Thus the second rule argues that the standard for any true knowledge should be the certitude demanded of demonstrations in arithmetic and geometry. The third rule begins to specify what this standard of true knowledge entails. The mind should be directed not by tradition, authority, or the history of the problem, but only by what can clearly be observed and deduced.

There are only two mental operations that are permissible in the pure use of reason. The first is intuition, which Descartes defines as "the undoubting conception of an unclouded and attentive mind"; the second is deduction, which consists of "all necessary inference from other facts that are known with certainty. "The basic assumption underlying these definitions is that all first principles are known by way of self-evident intuitions and that the conclusions of this "seeing into" are derived by deduction. The clarity and distinctness of ideas are for Descartes the conceptual counterpart of human vision. (For example, man can know the geometry of a square just as distinctly as he can see a square table in front of him.)

Many philosophers recognized the ideal character of mathematical reasoning, but no one before Descartes had abstracted the conditions of such thinking and applied it generally to all knowledge. If all science is unified by man's reason and if the proper functioning of the mind is identified with mathematical thinking, then the problem of knowledge is reduced to a question of methodology. The end of knowledge is true judgment, but true judgment is equivalent to mathematical demonstrations that are based on intuition and deduction. Thus the method for finding truth in all matters is merely to restrict oneself to these two operations.

According to the fourth rule, "By method I mean certain and simple rules, such that if a man observe them accurately, he shall never assume what is false as true ... but will always gradually increase his knowledge and so arrive at a true understanding of all that does not surpass his powers." The remaining sixteen rules are devoted to the elaboration of these principles or to showing their application to mathematical problems. In Descartes's later works he refines these methodological principles, and in the Meditations he attempts a metaphysical justification of this type of reasoning.

By 1634 Descartes had written his speculative physics in a work entitled The World. Unfortunately, only fragments survive because he suppressed the book when he heard that Galileo's Dialogue on the Two Great Systems of the Universe had been condemned by the Catholic Church because of its advocacy of Copernican rather than Ptolemaic astronomy. Descartes also espoused the Copernican theory that the earth is not the center of the universe but revolves about the sun. His fear of censure, however, led him to withdraw his work. In 1634 he also wrote the brief Treatise on Man, which attempted to explain human physiology on mechanistic principles.

Discourse and Meditations

In 1637 Descartes finished Discourse on Method, which was published together with three minor works on geometry, dioptrics, and meteors. This work is significant for several reasons. It is written in French and directed to men of good sense rather than professional philosophers. It is autobiographical and begins with a personal account of his education as an example of the need for a new method of conducting inquiry.

The work contains Descartes's vision of a unity of science based on a common methodology, and it shows that this method can be applied to general philosophic questions. In brief, the method is a sophistication of the earlier Rules for the Direction of the Mind. In the Discourse Descartes presents four general rules for reducing any problem to its fundamentals by analysis and then constructing solutions by general synthesis.

Meditations on First Philosophy appeared in 1641-1642 together with six (later seven) sets of objections by distinguished thinkers including Thomas Hobbes, Antoine Arnauld, and Pierre Gassendi and the author's replies. The Meditations is Descartes's major work and is one of the seminal books in the history of philosophy. While his former works were concerned with elaborating a methodology, this work represents the systematic application of those rules to the principal problems of philosophy: the refutation of skepticism, the existence of the human soul, the nature of God, the metaphysical basis of truth, the extent of man's knowledge of the external world, and the relation between body and soul.

The first meditation is an exercise in methodological skepticism. Descartes states that doubt is a positive means of ascertaining whether there is any certain foundation for knowledge. All knowledge originates either from the senses or from the mind. Examples of color blindness, objects seen in perspective, and so on testify to the distortions inherent in vague sense perception. The recognition of these phenomena as distorted suggests a class of clear perceptions which are more difficult to doubt. But Descartes then points out that such images appear as clear to man in dreams as in an awakened state. Therefore all sensory experience is doubtful because sense data in itself does not indicate whether an object is seen or imagined, true or false.

What about the realm of pure ideas? Descartes simplifies the argument by asking whether it is possible to doubt the fundamental propositions of arithmetic and geometry. Man cannot doubt that two plus two equals four, but he may suspect that this statement has no reality apart from his mind. The standard of truth is the self-evidence of clear and distinct ideas, but the question remains of the correspondence of such ideas to reality. Descartes imagines the existence of an all-powerful "evil genius" who deceives man as to the content of his ideas, so that in reality two plus two equals five.

The second meditation resolves these skeptical issues in a deceptively simple manner by arguing that even if it is doubtful whether sense images or ideas have objects, it is absolutely true that man's mind exists. The famous formula "I think, therefore, I am" is true even if everything else is false. Descartes's solution is known as subjectivism, and it is a radical reversal of previous theories of knowledge. Whereas nature had been assumed to be the cause of man's images and ideas, Descartes states that man is a "thinking thing" whose subjective images and ideas are the sole evidence for the existence of a world.

The third meditation demonstrates that God is "no deceiver," and hence clear and distinct ideas must have objects that exactly and actually correspond to them. Descartes argues that the idea of God is an effect. But an effect gets its reality from its cause, and a cause can only produce what it possesses. Hence either Descartes is a perfect being or God exists as the cause of the idea of God.

The fourth meditation deals with the problem of human error; insofar as man restricts himself to clear and distinct ideas, he will never err. With this connection between ideas and objects Descartes can emerge from his doubts about knowledge. The external world can be known with absolute certainty insofar as it is reducible to clear and distinct ideas. Thus the fifth meditation shows the application of methodology to material reality in its quantifiable dimensions, that is, to the extent to which material reality can be "the object of pure mathematics."

The sixth, and final, meditation attempts to explain the relation between the human soul and the body. Since Descartes believed in mechanism, there could be no absolute connection between a free soul and a bodily machine. After considerable hesitation he expresses the relation between mind and matter as a "felt union." The body is the active faculty that produces the passive images and imaginings man finds in his mind. Actually Descartes's explanation is logically impossible in terms of the "subjective" separation of mind; similarly, the unresolved dualism of the "felt union" violates the principle of assenting only to clear and distinct ideas.

The remainder of Descartes's career was spent in defending his controversial positions. In 1644 he published the Principles of Philosophy, which breaks down the arguments of the Meditations into propositional form and presents extra arguments dealing with their scientific application. In 1649 Descartes accepted an invitation from Queen Christina of Sweden to become her teacher. There he wrote The Passions of the Soul, which is a defense of the mind-body dualism and a mechanistic explanation of the passions. But Descartes's health was undermined by the severity of the northern climate, and after a brief illness he died in Stockholm in 1650.

Further Reading

• The most complete edition of Descartes's works in English is The Philosophical Works of Descartes, translated by Elizabeth S. Haldane and G.T.R. Ross (2 vols., 1955), although many editions of individual works in new translations are available in paperback. The standard biography is Haldane's Descartes: His Life and Times (1905; repr. 1966). Other biographical studies include Stephen Gaukroger, Descartes: An Intellectual Biography (1995), as well as Geneviève Rodis-Lewis Descartes: A Biography (trans. 1998), and Richard Watson, Cogito, Ergo Sum: The Life of Rene Descartes (2002). The best general introductions to Descartes's philosophy are A. Boyce Gibson, The Philosophy of Descartes (1932); Stanley V. Keeling, Descartes (1934; 2d ed. 1968); and Albert G. A. Balz, Descartes and the Modern Mind (1952). Works on specialized topics of an analytic or critical nature include Norman Kemp Smith, Studies in the Cartesian Philosophy (1902) and New Studies in the Philosophy of Descartes: Descartes as Pioneer (1952); Jacques Maritain, Three Reformers: Luther Descartes, Rousseau (trans. 1928) and The Dream of Descartes (trans. 1944); and Leslie J. Beck, The Method of Descartes: A Study of the Regulae (1952).