DESCARTES, RENÉ

French philosopher, also called Cartesius; b. La Haye, Touraine, March 31, 1596; d. Stockholm, Feb. 11, 1650. The philosophy of Descartes has been described as a turning point or watershed in European thought. Descartes himself has been called the father of modern philosophy and said to mark the intellectual transition from the Middle Ages to the modern world. These descriptions are acceptable provided it is understood, as modern scholars have emphasized, that while there is much that is genuinely new in his philosophy, there is also a continuity with the scholasticism that preceded it.

Life and Works. Descartes, the son of a family of minor nobility, was a pupil at the famous Jesuit college of La Flèche from 1604 to 1612. His studies included the usual classics, philosophy (physics, logic, and metaphysics, which may be roughly described as Suarezian in tendency), and mathematics. The last subject made a deep impression on the boy "because of the certainty of its proofs and the evidence of its reasonings." He completed his studies at Poitiers by taking a licentiate in law. A brief period of military service, and a voyage in Italy, were followed by a two-year stay in Paris where he met Cardinal Bérulle and Marin Mersenne, who became his lifelong friend and correspondent. In 1628 Descartes went to Holland where, in various towns, he spent the rest of his life and wrote his major works. The Discourse on Method was published in 1637. The Latin edition of the Metaphysical Meditations was published in 1641 (French translation in 1647). The Principles of Philosophy appeared

in Latin in 1644, the French translation in 1647; and finally the Passions of the Soul in 1649. Both the Regulae, probably composed in 1628, and the two treatises Man and the World are posthumous publications. Descartes was called to Sweden by Queen Christina and after only six months there, he died, fortified by the rites of the Church.

Cartesian Method. Descartes's preoccupation with methodology can be seen from his earliest works, the unpublished and incomplete Regulae and the Discourse, and he asserts repeatedly that the supreme question for philosophy is that of method. At the basis of this assertion is his view that the human mind, in its natural and unperverted state and insofar as it functions in accordance with its nature, cannot fail to think truly. The rules by which one is to search, that is, the method, are to be found by a careful reflection upon the human mind, by a study of its procedure when it functions purely and when its natural power of grasping truth is not corrupted or hampered by "prejudices." Method is not merely an instrument for constructing knowledge; it expresses the very nature of mind. Thus the problem of method is identical with the problem of the nature and limits of human knowledge.

Influence of Mathematics. The Cartesian conception of method was derived, as Descartes himself tells us in the autobiographical passages of the Discourse, from a personal dissatisfaction with the philosophical and scientific doctrines he was taught and, more positively, from a reflection on, and practice of, the procedure of the mathematical sciences. Impressed, as Immanuel Kant was to be, by the striking achievements of these sciences, he attempted to formulate their methodological principles in most general terms and, in so doing, thought he could constitute a general theory of method.

If, he argued, one reflects upon the certainty of mathematical demonstration, he finds that it depends upon fulfilling two main conditions: (1) one must start from selfevident data, and (2) every step in the progress from the self-evident data must be self-evident. No conclusion must be affirmed unless it follows from an uninterrupted sequence of self-evident data. To these two conditions of the certainty of demonstration correspond two functions of the intellect: (1) intellectual intuition (intuitus ), the power of apprehending the self-evident data, and (2) deduction, the power of moving, by an uninterrupted sequence of self-evident steps, from the data to their consequents. These two operations of the intellect are the primary conditions of all knowledge and express the very nature of the intellect. No theory of method can teach the intellect to perform them, for they are presupposed in all learning. A theory of method can do no more than facilitate their right use.

Intuition. By intellectual intuition is meant a conception of "a pure and attentive mind," such that no doubt whatever can remain as to what it is one conceives. The objects conceived are "simple natures," simple ideas, or two elements of an idea in immediate and necessary connection. Two conditions are required: the data must be conceived "clearly and distinctly" and they must be apprehended all at once and not successively. To apprehend the elements of a self-evident proposition "clearly" means to have the apprehended content present to the mind that is "attending" to it; to apprehend it "distinctly" means to have before the mind precisely the relevant content, neither more nor less.

Deduction. The second primary operation of the intellect is deduction, which involves the use of intellectual intuition in all its stages and is, as it were, a process by which intuition extends itself so as to comprehend within itself a complex of intuitions. It differs from the traditional subsumptive syllogism of formal logic, but is akin to the ἀποδεικτικòς συλλογισμός of Aristotle. The movement of thought is deduction. Insofar as the mind could retain, in a single undivided vision, all the single steps of the whole process, the completed deduction would be an intellectual intuition, and would possess the self-evidence of immediate presence, the praesens evidentia that is essential to the mind's certainty.

Where the demonstration must depend to some extent on memory, and accordingly, in the more complex cases where the data do not form a single chain of linear deductions but many interconnected groups of linear deductions, or what, Descartes calls, a network of chains, a second form of deduction called enumeration is required. Its function is to assist, and in a sense eliminate as far as possible, memory by arranging and preparing the data and by introducing and ordering them so as to facilitate the unbroken movement of illation.

Applications of the Method. The four "easy and certain rules" of the Discourse are the somewhat simplified,

almost dangerously simplified, expression of the methodological doctrine summarized above, omitting many important details. It should also be noted that the Discourse itself is only a preface to a volume containing three "exercises in method," that is, three applications of the method to various problems: the Dioptric, in which Descartes discusses and lays down the laws of refraction; the Meteors, in which he discusses the nature of light and the rainbow and approaches Newton's discovery of the composite nature of white light; and the Geometry, which is the basis of most of his fame as a mathematician and which won him his title as the founder of analytic geometry.

Analytic Geometry. This last work reproduces the fundamental characteristic of the method and illustrates the reduction of a problem to its most general and simple form. The representation of a curve is simplified by relating it, by putting it "into proportion" with the lengths of two straight lines—than which, says Descartes, one can find in the field of continuous magnitudes, no other objects "more capable of being distinctly represented," since "straightness" is a simple nature or idea. Then curved lines can be expressed algebraically in terms of an equation involving the perpendicular distance of a point to two perpendicular lines of reference. A point in a plane can be uniquely determined when its distances (usually designated x and y ) from the lines of reference (the coordinates, as G. W. leibniz was to name them) are known. With this knowledge, an equation can be formulated, F (xy ) = 0, that expresses a property true of every point of the curve. For every curve, some relationship can be shown to exist between the coordinates of a point anywhere on it. A curve may also be defined in terms of an equation involving x and y. And when two or more curves have the same coordinates, their points of intersection may also be found by the common solution of their equations. A curve has been simplified by reduction to an equation that is ultimately soluble by two straight lines: simple ideas that are the proper objects of intellectual intuition. The rest of the Geometry is a continuation of the procedure of analytical simplification, linked to the solution of the problem of Pappus and the required locus of a point set therein.

Transition to Metaphysics. Despite Descartes's admiration for the mathematical sciences, on which he based his method, his enthusiasm for his own demonstrations and their use in the Geometry is limited. In the course of his life after 1637 he showed a singular lack of interest in possible developments of the geometry that was to be a fertile source of inspiration to succeeding generations of mathematicians. The rest of the Discourse, the Meditations, and part of the Principles are devoted to his philosophical doctrines. But the transition from methodological problems to the study of metaphysics is not a mere accidental one. For, as is clear from the argument of the Meditations (which constitute the most elaborate of his philosophical expositions), to metaphysics falls the responsibility of conferring validity on the method, and, by implication, on the natural sciences. When Descartes, in the Principles (1.13), makes the strange statement that an atheist cannot possess knowledge in the strict sense, he means by atheist someone whose knowledge is not based on a suitable metaphysic.

Methodical Doubt. What one needs for a sound metaphysics is some apprehension that is clear and distinct, that refers to some existent, and that can be known with certainty. The first rule of the method is to rid the mind of prejudices. This is Descartes's starting point: the application of methodical doubt, a universal doubt applied to all accepted ideas, opinions, and beliefs. It may be noted that Descartes excepts from this universality the moral axioms, as a practical expediency, and the beliefs of his faith. His is not, like the skeptic's, a mere passive state of wavering indecision; it is a free and deliberate action pursued to its logical limit.

When one analyzes "the things which can be doubted," it is not necessary "to show that the whole of these are false." A preliminary classification of the sources and kinds of belief enables one to group them and test typical members, not for their falsity but for their doubtfulness. In replying to Father Bourdin, Descartes uses a homely metaphor: "Supposing a man had a basket of apples and feared that some might be rotten…would he not first tip out the whole lot…then having chosen those which he saw not to be rotten, he would place them again in the basket" (Oeuvres 7:481). Thus, the phenomena of illusions, hallucinations, etc., show that the senses are un-trustworthy, and the doubt applies to common beliefs based on sense-experience, even to the existence of the external world and one's own body. Psychologically, one may not be able to doubt them; logically, there are no grounds for asserting their certainty.

Even the conclusions of the exact sciences of mathematics, apparently indubitable, may be subject to a systematic defect of human minds or, possibly, a systematic deception of a "malignant demon," all-powerful. This last hypothesis, a literary device, is a hypothetical reformulation of his methodological principle, reversed into the proposition that the human mind cannot attain truth. If a single belief can be asserted in this "deep water" of universal uncertainty, then one can find a starting point, for that which destroys the strongest possible doubt must be itself, ipso facto, the greatest possible certitude.

Cogito Ergo Sum. This single assertion Descartes finds in the famous Cogito ergo sum, "I think, therefore I am." Even if I am deceived, there must exist an "I" who is deceived. It is impossible that I should doubt or be deceived, and yet not exist at the moment of doubting or being deceived. It should be noted that "thought," at the time of Descartes, had a wider connotation than now: it embraced not only thought but all mental data, will, feeling, perception, etc. "I am" is an immediate consequence, not an inference (despite the ergo ) of "I think," and it establishes a starting point because it is clear and distinct, it essentially refers to an existent, and it can be seen to be indubitably certain. But, it should also be noted, at this point in the argument all that has been established is the existence of a self as a thinking being, as and insofar as it thinks; in other words, not as a being possessing a body, senses, etc.

God's Existence. The next major step in the argument is to prove the existence of God, which is needed, according to Descartes, to extend the universality of the criterion of evidence beyond the privileged instance of the Cogito. This step is, as it were, the reflection of the hyperbolic "malignant demon." Descartes offers three proofs that all tend to demonstrate God, not as First Cause, but as a Perfect Being whose veracity will be the guarantee of man's clear and distinct ideas. It is impossible here to analyze the logical structure of these arguments. The general tenor is that a being that thinks, that doubts, errs, etc., knows that it is imperfect and finite; yet it could not be clearly aware of its own essential finitude and imperfection, if it did not also have in itself the idea of something infinite and perfect. The mind does not build the negative idea of infinitude by negating the limitations: it forms the idea of finitude by introducing a limit, which is a negation, into the idea of infinitude. The mind that produces an idea must at least be at the same level of perfection as the idea it produces, and therefore only an infinite being, that is God, can produce the idea of God.

Cartesian Dualism. The veracity of God establishes for Descartes the possibility of attaining knowledge of innumerable other propositions whose truth is certain. It is also the veracity of God that explains the presence in man's mind of clear and distinct innate ideas, and justifies his assertion of their validity and their conformity with the real world created by God. Man has two clear and distinct ideas, of soul and of body. The nature of the soul, as described in the Cogito, is to think, to be conscious. Conversely, the idea of body or matter does not include consciousness; it excludes it. When one thinks of body or matter, he may think of color, weight, hardness, shape, and other secondary qualities. But analysis shows that the essential nature of matter is spatial extension, figure and movement being regarded as modifications or modes of extension.

The consequences of this definition are radical, both for Cartesian doctrine and the future of the physical sciences. An obvious dualism of mind and matter is thereby created, and, given the nature of matter, the physical sciences assume a purely quantitative basis. An immediate problem for Descartes's doctrine was that of the unity of the human being, for he has rejected the hylomorphic solution. He asserts, somewhat inconsistently, that there is one idea that, although unclear and indistinct, is nevertheless certain, that is, the idea of the substantial union of the body and soul. But he offers no further solution as to how the two "substances" can and do unite, leaving the field open to the not very satisfactory solutions of occa sionalism, as proposed by N. malebranche and Leibniz (see mind-body problem). It can, however, be seen that the radical separation of thought and extension leads to a purely mechanistic conception of the physical sciences.

Physical Sciences. One direct consequence of this aspect of Cartesian doctrine is that all terrestrial and celestial phenomena, chemical as well as physical, are reduced fundamentally to the one science of what one should call physics, itself ideally to be formulated in mathematical formulas (see philosophy and science; mechanism). Descartes goes further, logically so in his own terms, by including also the biological sciences within the mechanistic scheme. There is no difference of principle in the explanation of the organic and the inorganic, since they are only modes of "matter." Hence, the well-known theory of "animal-machines"; the same can be said of the human body, which is merely differentiated from inanimate matter by a greater complexity. The simile often used of the body is that of a watch; a simile used by many later Cartesians, e.g., A. geulincx and Leibniz. Animals, not having the power of thought, are pure automata.

The physical theories of Descartes were originally set forth in the World, which was not completed or published in his lifetime, and in the third part of the Principles. They rest upon the metaphysical conclusions of the Meditations. The greater part of his scientific theories have long been discarded; they form part of the history of science. Descartes's theory of vortexes was shown by Newton to be impossible as a dynamical system; its chief merit was that it was a brilliant attempt to present a theory in which all the celestial phenomena could be rationally explained by mechanical processes. Descartes enunciates three primary laws of motion (or laws of nature, as he calls them) and seven secondary laws of "impact," the latter to a large extent incorrect. The fixed amount of motion in the universe is based on the immutability of God. Descartes's main achievement was in the field of optics, where he established the law of the refraction of light and adumbrated the undulatory theory of light. The Principles contains, in the latter parts, mainly obsolete scientific speculation.

Psychology and Free Will. Descartes did not elaborate a system of ethics. The Passions of the Soul and the correspondence with Princess Elizabeth of Bohemia are more a psychophysical theory of the emotions, presupposing the fundamental doctrine of the complete separation of the body and soul and the paradox, for Cartesian philosophy, of their "substantial union." It is therefore a theory of interaction, wherein what is "a passion" in the soul is "an action" of the body, the one being caused by the other. The perception of passions is, of course, different and must be distinguished from them. The problem then is how one can control this interaction. The stress on self-control and the various rules, adopted from the four rules of the method, have much in common with Stoic doctrine, and Descartes, contrary to his usual habit, quotes Seneca in his letters.

There is no discussion of free will as such in these writings. The reason for this omission is that for Descartes, free will is self-evident, a primary datum, an innate idea, logically implicit in Cogito ergo sum, since the hyperbolical doubt implies the possibility of choosing to doubt even such things as the existence of the external world, the truths of mathematics, etc. The nature and extent of human freedom, once the existence of God is established, does involve further problems, problems that in the 17th century were the subjects of the great controversies of jansenism and molinism. It is possible to find, in the works of Descartes, expressions of his views that tend toward both positions, although the expressions of his latter writings tend away from the extremist views of Jansenism. On the whole, his major interest was in the epistemological problem of error and the role of the will therein. He was chary of theological disputes and was generally content to assert both the freedom of will and the omnipotence of God and assert that the problem transcends the human mind.

Critique and Evaluation. The position of Descartes in the history of philosophy is a puzzling one. Certain facts are clear. His contributions to experimental science were without great value; his physical theories were discarded within 100 years; only his mathematical discoveries had permanent value. On the purely metaphysical side, he has not the wider brilliance of Leibniz or the depth of B. spinoza, the other two "rationalists" of the 17th century. Yet his work constitutes a nodal point in the history of thought; he is rightly considered the father of modern thought, for he gathered together previously unconnected strands of thought into a single train of thought and gave new impetus and direction to all subsequent inquiry. He set men thinking in new directions and, in this sense, was the most influential philosopher since Plato.

Merits and Defects. In a certain sense, the merits and defects of Descartes's philosophy have prolonged its influence in the varying emphases placed on the different, and not too consistent, aspects by thinkers of subsequent generations. It should be noted that even in the task of exegesis of Descartes's own doctrine, as the vast literature of commentary testifies, there is far from unanimity. Descartes has been variously identified as a skeptic, a phenomenalist, a realist, and a subjective idealist; even the modern school of phenomenology would claim descent from Descartes. The apparent simplicity and the economy of his writing hide what is often a heroic attempt to maintain his system through a series of improvisations. These were revealed by his own intellectual probity when he attempted to answer the objections raised by his contemporaries, especially the sharp critic Arnauld. Some of the subtle and insidious mistakes made by Descartes sent generations of philosophers on a wild-goose chase that still continues. To this extent only, can one accept J. Maritain's statement that "Descartes [or Cartesianism] has been the great French sin in modern history." Moreover, Descartes used an existent terminology and often could not escape entanglement in its content and implications. The new wine was too strong for the old bottles.

Theory of Knowledge. Modern epistemology, or the problem of knowledge, which has occupied most philosophers since the time of Descartes, may be said to have grown from the Cartesian use of the word "idea," in other words, from his theory of "representative ideas," in which ideas are regarded as objects of mind. This theory, a direct consequence of his dualism, was later accepted by Leibniz and John locke. If what is perceived is in the mind, the obvious question arises as to the nature of what it is supposed to represent. If the mind of spirit and the material world are in absolute separation and antagonism, how is the fact of knowledge, which involves their interrelation, to be accounted for? Descartes is able to assert the reality of matter by the veracity of God. Insofar as he asserts a causality of interaction between body and mind, he breaks down his theory of innate ideas and opens the door to other kinds of ideas. To localize the point of contact in the "pineal gland" merely pushes the problem one stage further back.

General Influence. The Cogito itself has been the subject of controversy and criticism, ranging from the atomistic views of David hume and the logical analysts, to the criticisms of Kant, G. W. Hegel and J. P. Sartre. The great protagonist of "clear and distinct ideas" has led many historians of philosophy to different, and even opposed, interpretations of his doctrine. There are many loose ends, many inconsistent improvisations in his thought. The claim that he is the father of modern philosophy cannot be based on any general acceptance of his most cherished views; they have all been partially or totally rejected.

It has been said that the history of philosophy consists of footnotes to Plato. Modern philosophy, in a similar fashion, consists in an endeavor to solve, or dissolve, problems raised in an original manner by the vision and genius of Descartes. One point of controversy at least can be settled. It was fashionable at one time to throw doubt on the sincerity of Descartes's religious convictions. He was and died a Catholic, in "the faith of his nurse."

See Also: cartesianism; dualism; innatism; subjectivism; rationalism; philosophy, history of.

Bibliography: Works. Oeuvres, ed. c. adam and p. tannery, 12 v. (Paris 1897–1910); Correspondance, ed. c. adam and g. milhaud, 8 v. (Paris 1956–63); Philosophical Works, tr. e. s. haldane and G. R. T. ross, 2 v. (Cambridge, Eng. 1931–34; reprint New York 1955); Philosophical Writings, tr. n. k. smith (New York 1958); Philosophical Writings, ed. e. anscombe and p. t. geach (Edinburgh 1961); Selections, ed. r. m. eaton (New York 1927); Essential Works, tr. l. bair (New York 1961); Discours de la méthode, ed. É. h. gilson (Paris 1955); Geometry, tr. d. e. smith and m. l. latham (New York 1954). Studies. f. alquiÉ, Descartes: L'homme et l'oeuvre (Paris 1956); La Découverte métaphysique de l'homme chez Descartes (Paris 1950). a. g. a. balz, Descartes and the Modern Mind (New Haven 1952). l. j. beck, The Method of Descartes (Oxford 1952). j. chevalier, Descartes (new ed. Paris 1949). j. de finance, Cogito cartésien et réflexion thomiste (Paris 1946). a. b. gibson, The Philosophy of Descartes (London 1932). É. h. gilson, Études sur le rôle de la pensée médiévale dans la formation du système cartésien (Paris 1930). h. g. gouhier, La Pensée métaphysique de Descartes (Paris 1962). m. guÉroult, Descartes, selon l'ordre des raisons, 2 v. (Paris 1953). e. s. haldane, Descartes: His Life and Times (New York 1905). o. hamelin, La Système de Descartes (2d ed. Paris (1921). h. h. joachim, Descartes's Rules for the Direction of the Mind (London 1957). s. v. keeling, Descartes (London 1934). j. m. f. laporte, Le Rationalisme de Descartes (Paris 1945). j. maritain, The Dream of Descartes, tr. m. l. andison (New York 1944). g. rodis–lewis, La Morale de Descartes (2d ed. Paris 1962). n. k. smith, New Studies in the Philosophy of Descartes (London 1952). l. j. beck, The Metaphysics of Descartes (Oxford 1965).

[l. j. beck]

DESCARTES, RENÉ

DESCARTES, RENÉ (1596–1650), French philosopher. Descartes is held to be the father of modern philosophy and chief architect of the modern approach to the relationship between science and religion. The scholastic tradition, already ably criticized by Descartes's time, was in effect obviated by a new, universal metaphysical construction based on the conceptual apparatus of Descartes. The entire development of European philosophy, in all its diverse tendencies, has been dependent, directly or indirectly, on the Cartesian legacy. If it is true, as Whitehead said, that European philosophy consists of footnotes to Plato, modern European philosophy, in the same sense, consists of footnotes to Descartes.

Born to a noble Roman Catholic family, Descartes was educated in the physics and metaphysics of an Aristotelian and Thomist tradition, and in medicine and law. He joined the Dutch army, and, while in the Netherlands, became interested in mathematics and the new physics. Having traveled in various countries, he returned to France, where he outlined the first version of a new method of thinking based on mathematics (Rules for the Direction of the Mind), but he did not complete or publish it. After settling in the Netherlands, he maintained contact with scholars by letter; Marin Mersenne was his main correspondent. He passed the last year of his life in Sweden at the court of Queen Christina.

Descartes's aim was to use mathematics as a model for developing a fully unified form of human knowledge. He applied this method in his Treatise on the World. The trial of Galileo and condemnation of Galileo's Dialogues convinced Descartes not to print his own work, which clearly confirmed the heliocentric theory. In 1637 he published several parts of it with a methodological introduction, called The Discourse on Method, which was to become one of the greatest texts of modern thought. In 1641 he published his other major work, Meditations on First Philosophy, which had previously been sent to a number of scholars, among them Gassendi, Hobbes, and Arnauld; their objections and Descartes's replies were subsequently published with the main text. The Principles of Philosophy appeared in 1644 and The Passions of the Soul in 1649. Some other works and his voluminous correspondence were published posthumously.

The Discourse indicates that for Descartes philosophy was a methodological and conceptual basis for the sciences, to make them useful in the domination of nature. Although the metaphysical problems he discussed in his Meditations are not subordinated to this goal, it is clear that Descartes was interested only in matters that could be solved by rational means and that his mental attitude was essentially antihistorical.

Cartesian method demands that we accept as true only what is presented "clearly and distinctly" to our mind, leaving no room for doubt. We should suspend our judgment in all matters where the slightest doubt is possible, including all the truths of common sense, in order to find something that resists all doubts. Sense-perception does not provide us with any indubitable knowledge, since we cannot be a priori certain that we are not dreaming or that we are not being deceived by a malicious demon. But my very act of doubting, however far extended, and therefore the fact that I am thinking, cannot itself be doubted. And thus I find at least this one certainty in which I cannot be deceived: I think, and I, the thinker, must exist; no demon could induce me to err on this point. This reasoning, summarized in the famous formula "Cogito ergo sum," can be admitted as the basis of knowledge.

The cogito, accepted as a kind of epistemological absolute, is in Descartes's work an implicit challenge to the authority of tradition and an appeal to look for truth only in the reason of a thinking individual. And it implies that the only object that is directly and indubitably accessible to one's mind is its own activity; wherever else we start, our beliefs will be exposed to doubt.

While I grasp my existence as identical with the awareness of existence, I observe, according to Descartes, that nothing belongs necessarily to my nature except the fact that I think; therefore I may describe myself as a thinking thing, or thinking substance, or immaterial soul. This transition from "I think" to "I am a thinking substance" was strongly criticized by Descartes's contemporaries and later. It gave rise to the question, much debated in the twentieth century, whether or not the "self" or "I" can be described at all in "objective" categories.

Our mind, according to Descartes, has a natural light whereby it is capable of acquiring knowledge on most important issues without relying on sense-perception. We have in our mind a natural idea of God, or a perfect being. Since our mind clearly perceives that it is not perfect itself (of which the fact of doubting is evidence, if indeed evidence is needed), it could not have fabricated this idea, as a more perfect thing cannot be produced by a less perfect; consequently the very presence of this idea is a proof of the actual existence of the perfect being. This psychological argument for God's existence, like the ontological argument in traditional version, which Descartes accepts as well, implies nothing about God's presence and signs in the world. God's first function, in Descartes's construction, is to assure the reliability of human knowledge: being perfect, God cannot deceive us, therefore we can rely both on our commonsense belief in the reality of the material world and on our intellectual intuition. (Many critics pointed out the circularity in this reasoning: acts of intuition are necessary to acquire the certainty of the existence of God, who subsequently appears as a guarantor of the infallibility of those very acts.) We can thus affirm the reality of the material world.

Descartes conceived the material world, or "extension," in strictly mechanistic terms. All processes are explained by the laws of mechanics; living organisms behave according to the same principles that govern artificial automata; there is no specific realm of life. To be sure, human beings are endowed with an immaterial soul, which is the seat of all sensations; animals, having no soul, are no more than mechanisms, and their reactions are just mechanical movements. In human beings, organic (that is, mechanical) processes, should be distinguished from psychological events in the soul. The human organism does not differ from other mechanisms; its death is a physical phenomenon, whereas the separation of the soul is not the cause but the effect of death. The two substances—soul and body—that make up the human being cannot affect each other; therefore the question of how we can realize, in perception, the mechanical impacts of other things on our bodies and cause movements of our body by the sheer act of will becomes difficult to solve; and Descartes's followers, when trying to explain the unity of soul and body and their mutual influence, naturally tended to materialist or occasionalist explanations, none of which conformed to the master's doctrine, which implied both that the soul is absolutely free and capable of dominating the affects, and that the affects are passive states caused by the movement of blood.

Descartes's philosophy almost instantaneously produced new lines of division in European intellectual life. Though attacked, mainly for its rationalist rigor, by both Protestants (the school of Voetius) and Catholics (all Descartes's works were put on the Index of Prohibited Books in 1663), its impact was soon to be felt not only among philosophers, scientists, and physicians, but among theologians as well. In the Netherlands, Coccejus's school tried to apply Descartes's methods in theological investigations; in France, Malebranche and other occasionalists attempted a Catholic assimilation of a somewhat modified Cartesianism. In the Jansenist milieu the influence of Descartes was very strong. By the end of the seventeenth century few orthodox Cartesians remained, but the impact of the doctrine was felt throughout the early French Enlightenment; its general rationalist and determinist approach laid the foundation of eighteenth-century materialism, while its skeptical side and the cogito were crucially important in the rise of modern idealism, starting with Berkeley.

Although there are no reasons to doubt that Descartes himself believed in God and in the immortality of the soul, his philosophy made God absent in the world and thus useless in interpreting it. Descartes was not, strictly speaking, a deist, insofar as, according to him, the force needed to sustain the universe in existence is the same as that needed to create it; yet he contributed decisively to the deist and atheist movements of the subsequent centuries. He was the modern founder of totally secularized thinking. Outstanding twentieth-century Thomists (Gilson, Maritain) saw in Descartes the main author of what they believed to be the aberration of modern intellectual life, of its individualist, idealist, and rationalist tendencies. And the problem of the transition from the cogito to the world and vice versa has remained, thanks to Descartes, one of the crucial issues in modern phenomenology and existential philosophy.

Bibliography

Works by Descartes

Correspondance. 8 vols. Edited by Charles Adam and Gérard Milhaud. Paris, 1936–1963.

Descartes: Philosophical Writings. Selected, translated, and edited by Elizabeth Anscombe and P. T. Geach. Edinburgh, 1964. Contains a good bibliography.

Œuvres de Descartes. 2d ed. 12 vols. Edited by Charles Adam and Paul Tannery. Paris, 1956–1957.

Philosophical Letters. Translated and edited by Anthony Kenny. Oxford, 1970.

Works about Descartes

Alquié, Ferdinand. La découverte métaphysique de l'homme chez Descartes. 2d ed. Paris, 1966.

Doney, Willis, ed. Descartes: A Collection of Critical Essays. Garden City, N.Y., 1967.

Gilson, Étienne. La doctrine cartésienne de la liberté et la théologie. Paris, 1915.

Gilson, Étienne. Études sur le rôle de la pensée médiévale dans la formation du système cartésien. Paris, 1930.

Gouhier, Henri. La pensée religieuse de Descartes. Paris, 1924.

Laporte, Jean. Le rationalisme de Descartes. 2d ed. Paris, 1950.

Leroy, Maxime. Descartes, le philosophe au masque. Paris, 1929.

Mouy, Paul. Le développement de la physique cartésienne. Paris, 1934.

Sebba, Gregor. Bibliographia Cartesiana. The Hague, 1964.

Leszek Kolakowski (1987)

Descartes, René Du perron

(b. La Haye, Touraine, France, 31 March 1596; d. Stockholm, Sweden, 11 February 1650)

natural philosophy, scientific method, mathematics, optics, mechanics, physiology.

Fontenelle, in the eloquent contrast made in his Éloge de Newton, described Descartes as the man who “tried in one bold leap to put himself at the source of everything, to make himself master of the first principles by means of certain clear and fundamental ideas, so that he could then simply descend to the phenomena of nature as to necessary consequences of these principles.” This famous characterization of Descartes as the theoretician who “set out from what he knew clearly, in order to find the cause of what he saw,” as against Newton the experimenter, who “set out from what he saw, in order to find the cause,” has tended to dominate interpretations of both these men who “saw the need to carry geometry into physics.”¹

Descartes was born into the noblesse de robe, whose members contributed notably to intellectual life in seventeenth-century France. His father was conseiller to the Parlement of Brittany; from his mother he received the name du Perron and financial independence from property in Poitou. From the Jesuits of La Flèche he received a modern education in mathematics and physics—including Galileo’s telescopic discoveries—as well as in philosophy and the classics, and there began the twin domination of imagination and geometry over his precocious mind. He described in an early work, the Olympica, how he found “in the writings of the poets weightier thoughts than in those of the philosophers. The reason is that the poets wrote through enthusiasm and the power of imagination.” The seeds of knowledge in us, “as in a flint were” brought to light by philosophers “through reason; struck out through imagination by poets they shine forth more brightly.”² Then, after graduating in law from the University of Poitiers, as a gentleman volunteer in the army of Prince Maurice of Nassau in 1618 he met Isaac Beeckman at Breda. Beeckman aroused him to self-discovery as a scientific thinker and mathematician and introduced him to a range of problems, especially in mechanics and acoustics, the subject of his first work, the Compendium musicae of 1618; published posthumously in 1650. On 26 March 1619 he reported to Beeckman his first glimpse of “an entirely new science,”³ which was to become his analytical geometry.

Later in the year, on 10 November, then in the duke of Bavaria’s army on the Danube, he had the experience in the famous poêle (lit. “stove,” “well-heated room”), claimed to have given direction to the rest of his life. He described in the Discours de la mèthode how, in a day of solitary thought, he reached two radical conclusions: first, that if he were to discover true knowledge he must carry out the whole program himself, just as a perfect work of art or architecture was always the work of one master hand; second, that he must begin by methodically doubting everything taught in current philosophy and look for self-evident, certain principles from which to reconstruct all the sciences. That night, according to his seventeenthcentury biographer Adrien Baillet, these resolutions were reinforced by three consecutive dreams. He found himself, first, in a street swept by a fierce wind, unable to stand, as his companions were doing, because of a weakness in his right leg; second, awakened by a clap of thunder in a room full of sparks; and third, with a dictionary, then a book in which he read Quid vitae sectabor iter? (“What way of life shall I follow?”), then verses presented by an unknown man beginning Est et non; he recognized the Latin as the opening lines of two poems by Ausonius. Before he finally awoke he had interpreted the first dream as a warning against past errors, the second as the descent of the spirit of truth, and the third as the opening to him of the path to true knowledge. However this incident may have been elaborated in the telling, it symbolizes both the strength and the hazards of Descartes’s unshakable confidence and resolve to work alone. But he did not make his vision his life’s mission for another nine years, during which (either before or after his tour of Italy from 1623 to 1625) he met Mersenne, who was to become his lifelong correspondent, and took part in scientific meetings in Paris. The next decisive incident, according to Baillet, was a public encounter in 1628 in which he demolished the unfortunate Chandoux by using his method to distinguish sharply between true scientific knowledge and mere probability. Among those present was the influential Cardinal de Bérulle, who a few days later charged him to devote his life to working out the application of “his manner of philosophizing... to medicine and mechanics. The one would contribute to the restoration and conservation of health, and the other to some diminution and relief in the labours of mankind.”⁴ To execute this design he withdrew, toward the end of the year, to the solitary life in the Netherlands which he lived until his last journey to Stockholm in 1649, where, as Queen Christina’s philosopher, he died in his first winter.

The primarily centrifugal direction of Descartes’s thought, moving out into detailed phenomena from a firm central theory (in contrast with the more empirical scientific style of Francis Bacon and Newton), is shown by the sequence of composition of his major writings. He set out his method in the Rules for the Direction of the Mind, left unfinished in 1628 and published posthumously, and in the Discours de la méthode, written in the Netherlands along with the Météores, La dioptrique, and La géométrie, which he presented as examples of the method. All were published in one volume in 1637. At the same time his investigation into the true ontology led him to the radical division of created existence into matter as simply extended substance, given motion at the creation, and mind as unextended thinking substance. This conclusion he held to be guaranteed by the perfection of God, who would not deceive true reason. How these two mutually exclusive and collectively exhaustive categories of substance could have any interaction in the embodied soul that was a man was a question discussed between Gassendi, Hobbes, and Descartes in the Objections and Replies published with his Meditations on First Philosophy in 1641.

It was from these first principles that he had given an account in Le monde, ou Traité de la lumière of cosmogony and cosmology as products simply of matter in motion, making the laws of motion the ultimate “laws of nature” and all scientific explanation ultimately mechanistic. This treatise remained unpublished in Descartes’s lifetime. So too did the associated treatise L’homme, in which he represented animals and the human body as sheer mechanisms, an idea already found in the Rules. He withheld these essays, on the brink of publication, at the news of Galileo’s condemnation in 1633, and instead published his general system of physics, with its Copernicanism mitigated by the idea that all motion is relative, in the Principles of Philosophy in 1644. Finally, he brought physiological psychology within the compass of his system in Les passions de l’âme in 1649. This system aimed to be as complete as Aristotle’s, which it was designed to replace. It was not by chance that it dealt in the same order with many of the same phenomena (such as the rainbow), as well as with others more recently investigated (such as magnetism).

A comparison of Descartes’s performance with his program of scientific method presents a number of apparent contradictions. He made much of the ideal of a mathematically demonstrated physics, yet his fundamental cosmology was so nearly entirely qualitative that he came to fear that he had produced nothing more than a beautiful “romance of nature.”⁵ His planetary dynamics was shown by Newton to be quantitatively ridiculous. He wrote in the Discours, “I noticed also with respect to experiments [expériences] that they become so much the more necessary, the more we advance in knowledge,”⁶ yet his fundamental laws of nature, the laws of motion and impact, had to be dismantled by Huygens and Leibniz for their lack of agreement with observation. These apparent contradictions may be resolved in the contrast between Descartes’s theoretical ideal of completed scientific knowledge and the actual process and circumstances of acquiring such knowledge. For the modern reader to pay too much attention to his mechanics and to the Principles, a premature conception of completed science, can obscure Descartes’s firm grasp of the necessity for observation and experiment already expressed in the Rules in his criticism “of those philosophers who neglect experiments and expect truth to rise from their own heads like Minerva from Jupiter’s.”⁷

No other great philosopher, except perhaps Aristotle, can have spent so much time in experimental observation. According to Baillet, over several years he studied anatomy, dissected and vivisected embryos of birds and cattle, and went on to study chemistry. His correspondence from the Netherlands described dissections of dogs, cats, rabbits, cod, and mackerel; eyes, livers, and hearts obtained from an abattoir; experiments on the weight of the air and on vibrating strings; and observations on rainbows, parahelia, and other optical phenomena. Many of his scientific writings reflect these activities and show sound experimental knowledge, although the extreme formalism of his physiological models obscures the question of his actual knowledge of some aspects of anatomy. Attention to the whole range of his scientific thought and practice shows a clear conception not only of completed scientific knowledge but also of the roles of experiment and hypothesis in making discoveries and finding explanations by which the body of scientific knowledge was built up.

Descartes’s conception of completed scientific knowledge was essentially that envisaged by Aristotle’s true scientific demonstration. It was the geometers’ conception of a system deduced from selfevident and certain premises. He wrote

In physics I should consider that I knew nothing if I were able to explain only how things might be, without demonstrating that they could not be otherwise. For, having reduced physics to mathematics, this is something possible, and I think that I can do it within the small compass of my knowledge, although I have not done it in my essays.⁸

His optimism about the possibility of achieving such demonstrations seems to have depended on which end of the chain of reasoning he was contemplating. When considering the results of his analysis reducing created existence to extension (with motion) and thought, he seems to have been confident that it would be possible to show that from these “simple natures” the composite observed world must follow. It may be argued that his treatment of motion failed just where his a priori confidence led him to suppose that his analysis (of what was soon seen to be an insufficient range of data) placed his first principles beyond the need for empirical test. But when considering the chain lower down, nearer this complex world, he was more hesitant. He wrote to Mersenne:

You ask me whether I think what I have written about refraction is a demonstration. I think it is, at least as far as it is possible, without having proved the principles of physics previously by metaphysics, to give any demonstration on this subject... as far as any other question of mechanics, optics, or astronomy, or any other question which is not purely geometrical or arithmetical, has ever been demonstrated. But to demand that I should give geometrical demonstrations of matters which depend on physics is to demand that I should do the impossible. If you restrict the use of “demonstration”to geometrical proofs only, you will be obliged to say that Archimedes demonstrated nothing in mechanics, nor Vitellio in optics, nor Ptolemy in astronomy, etc., which is not commonly maintained. For, in such matters, one is satisfied that the writers, having presupposed certain things which are not obviously contradictory to experience, have besides argued consistently and without logical fallacy, even if their assumptions are not exactly true.⁹

The paradox of Descartes as a natural scientist is that his grasp improved the more hopeless he found the immediate possibility of deducing solutions of detailed problems from his general first principles. Standing amidst the broken sections of a chain that he could not cast up to heaven, the experimentalist and constructor of hypothetical models came to life. In Descartes’s letter prefaced to the French translation of the Principles (1647), he wrote that two, and only two, conditions determined whether the first principles proposed could be accepted as true: “First they must be so clear and evident that the mind of man cannot doubt their truth when it attentively applies itself to consider them”; and secondly, everything else must be deducible from them. But he went on to admit,“It is really only God alone who has perfect wisdom, that is to say, who has a complete knowledge of the truth of all things.”¹⁰ To find the truth about complex material phenomena man must experiment, but as the sixth part of the Discours shows, the need to experiment was an expression of the failure of the ideal.

As well as being demonstrative, scientific knowledge had to be explanatory; for Descartes the two went together. He wrote, “I have described... the whole visible world as if it were only a machine in which there was nothing to consider but the shapes and movements [of its parts].”¹¹ To such a mechanism it was possible to apply mathematics and calculation, but it was the mechanism that explained. His insistence that even mathematical science without fundamental explanations was insufficient appears in his interestingly similar criticisms of Harvey for starting simply with a beating heart in explaining the circulation of the blood and of Galileo for likewise failing to reduce the mathematical laws of moving bodies to their ultimate mechanisms. He commented on the latter that “without having considered the first causes of nature, he has only looked for the reasons for certain particular effects, and that thus he has built without foundation.”¹² By this insistence Descartes here again extracted from the failure of his ideal a fundamental contribution to scientific thinking. He became the first great master to make the hypothetical model, or “conjecture,” a systematic tool of research.

Current natural philosophy accepted Aristotle’s absolute ontological distinction between naturally generated bodies (inanimate and animate) and artificial things made by man. Hence, in principle no humanly constructed imitation or model could throw real light on the naturally endowed essence and cause of behavior. This distinction had become blurred in the partial mechanization of nature made by some philosophers. Descartes’s innovation was to assert the identity of the synthesized artificial construction with the naturally generated product and to make this identification an instrument of scientific research:

And certainly there are no rules in mechanics that do not hold also in physics, of which mechanics forms a part or species [so that all artificial things are at the same time natural]: for it is not less natural for a clock, made of these or those wheels, to indicate the hours, than for a tree which has sprung from this or that seed to produce a particular fruit. Accordingly, just as those who apply themselves to the consideration of automata, when they know the use of some machine and see some of its parts, easily infer from these the manner in which others which they have not seen are made, so, from the perceptible effects and parts of natural bodies, I have endeavoured to find out what are their imperceptible causes and parts.¹³

This reduction made the principles of the mechanistic model the only principles operating in nature, thus bringing the objectives of the engineer into the search for the nature of things and throwing the entire world of matter open to the same form of scientific inquiry and explanation. Research, whether into cosmology or physiology, was reduced to the discovery and elucidation of mechanisms. He could construct in distant space the imaginary world of Le monde and L’homme, and later the world of the Principles, as explicitly and unambiguously hypothetical imitations of our actual world, made in accordance with the known laws of mechanics. The heuristic power of the model was that, like any other theory advanced in anticipation of facts, its own properties suggested new questions to put to nature. The main issue in any historical judgment of Descartes here is not whether his own answers were correct but whether his questions were fruitful. In insisting that experiment and observation alone could show whether the model corresponded with actuality, he introduced further precision into his theory of demonstration.

Descartes used the word demonstrer to cover both the explanation of the observed facts by the assumed theory and the proof of the truth of the theory. When challenged with the criticism that this might make the argument circular, he replied by contrasting two kinds of hypothesis.¹⁴ In astronomy various geometrical devices, admittedly false in nature, were employed to yield true conclusions only in the sense that they “saved the appearances.” But physical theories were proposed as true. He was persuaded of the truth of the assumption that the material world consisted of particles in motion by the number of different effects he could deduce, as diverse as the operation of vision, the properties of salt, the formation of snow, the rainbow, and so on. Thus he made range of application the empirical criterion of truth. He wrote in the Discours:

If some of the matters of which I have spoken in the beginning of the Dioptrique and the Météores should, at first sight, shock people because I have called them suppositions, and do not seem to bother about their proof, let them have the patience to read them carefully right through, and I hope that they will find themselves satisfied. For it seems to me that the reasonings are so interwoven that as the later ones are demonstrated by the earlier which are their causes, these earlier ones are reciprocally demonstrated by the later which are their effects. And it must not be thought that in this I commit the fallacy which logicians call arguing in a circle, for, since experience renders the majority of these effects very certain, the causes from which I deduce them do not so much serve to prove them as to explain them; on the other hand, the causes are proved by the effects.¹⁵

The test implied precisely by the criterion of range of confirmation was the experimentum crucis. This is the most obvious feature in common between Descartes’s logic of experiment and that of Francis Bacon. Descartes described its function in the Discours:

Reviewing in my mind all the objects that have ever been presented to my senses, I venture truly to say that I have not there observed anything that I could not satisfactorily explain by the principles I had discovered. But I must also confess that the power of nature is so ample and so vast and that these principles are so simple and so general, that I have observed hardly any particular effect that I could not at once recognize to be deducible from them in several different ways, and that my greatest difficulty is usually to discover in which of these ways it depends on them. In such a case, I know no other expedient than to look again for experiments [expériences] such that their result is not the same if it has to be explained in one of these ways as it would be if explained in the other.¹⁶

It was a logician rather than an experimenter who seems to have been uppermost in Descartes’s application of this criterion in the same way to very general assumptions, such as the corpuscularian natural philosophy, and to questions as particular as whether the blood left the heart in systole or in diastole. Descartes argued in La description du corps humain (1648–1649) that whereas Harvey’s theory that the blood was forced out of the heart by a muscular contraction might agree with the facts observed so far, “that does not exclude the possibility that all the same effects might follow from another cause, namely from the dilatation of the blood which I have described. But in order to be able to decide which of these two causes is true, we must consider other observations which cannot agree with both of them.”¹⁷ Harvey replied in his Second Disquisition to Jean Riolan.

As the great optimist of the scientific movement of the seventeenth century, Descartes habitually wrote as if he had succeeded in discovering the true principles of nature to such an extent that the whole scientific program was within sight of completion. Then, as Seth Ward neatly put it, “when the operations of nature shall be followed up to their staticall (and mechanicall) causes, the use of induction will cease, and syllogisme succeed in place of it.” But Descartes would surely have agreed with Ward’s qualification that “in the interim we are to desire that men have patience not to lay aside induction before they have reason.”¹⁸

NOTES

1. Fontenelle, Oeuvres diverses, new ed., III (The Hague, 1729), 405–406.

2. Part of the Olympica incorporated in the Cogitationes privatae (1619–1621); see Oeuvres, X, 217.

3.Oeuvres, X, 156.

4. Baillet. II, 165.

5.Ibid., preface, p. xviii.

6.Oeuvres, VI, 63.

7. Rule V: see Oeuvres, X, 380.

8. Letter to Mersenne, 11 Mar. 1640; see Oeuvres, III, 39. The “Essays” were the volume of 1637.

9. Letter to Mersenne, 27 May 1638; see Oeuvres, II, 141–142.

10.Oeuvres, IX. pt. 2, 2–3.

11.Principia philosophiae, IV, 188; Oeuvres, VIII, pt. 1, 315 (Latin);IX, pt. 2, 310 (French, alone with passage in square brackets).

12. Letter to Mersenne, 11 Oct. 1638; see Oeuvres, II, 380. For his comments on Harvey, see Discours V.

13.Principia philosophiae, IV, 203; Oeuvres, VIII, pt. 1, 326 (Latin); IX, pt. 2, 321–322 (French, alone with passage in square brackets).

14. Letter to J.-B. Morin, 13 July 1638; see Oeuvres, II, 197–202; cf. his letters to Vatier, 22 Feb. 1638, ibid., I, 558–565, and to Mersenne, I Mar. 1638, ibid., II, 31–32.

15.Oeuvres, VI, 76.

16.Ibid., pp. 64–65; cf. Principia philosophiae, III, 46; VIII. pt. 2,100–101; and IX, pt. 2, 124–125.

17.Oeuvres, XI, 241–242; cf. the comments on this controversy by J. B. Duhamel, “Quae sit cordis motus effectrix causa,” in Philosophia vetus et nova. II, Physica generalis, III.ii.2 (Paris,1684), 628–631.

18.Vindiciae academiarum (Oxford, 1654), p. 25.

BIBLIOGRAPHY

Descartes’s complete works can be found in Oeuvres de Descartes, C. Adam and P. Tannery, eds. 12 vols. (Paris,1897–1913), together with the revised Correspondence, C. Adam and G. Milhaud, eds. (Paris, 1936–). Besides these, primary sources for Descartes’s life are Adrien Baillet, La vie de Monsieur Descartes, 2 vols. (Paris, 1691), which should be read with C. Adam, Vie et oeuvres de Descartes (in Oeuvres, XII); Isaac Beeckman, Journal tenu... de 1604 à 1634, C. de Waard, ed., 3 vols. (The Hague,1939–1953): Marin Mersenne, Correspondance, C. de Waard, R. Pintard, B. Rochot, eds. (Paris, 1932–).

For Descartes’s philosophy and method and their background, see E. Gilson, Index scolastico-cartésien (Paris,1912); Études sur le rôle de la pensée médiévale dans la formation du système cartésien (Paris, 1930); Discours de la méthode: texte et commentaire (Paris, 1947); Alexandre Koyré, Entretiens sur Descartes (Paris-New York, 1944); G. Milhaud, Descartes savant (Paris, 1921); L. Roth, Descartes’ Discourse on Method (Oxford, 1937); H. Scholz, A. Kratzer, and J. E. Hofmann, Descartes (Münster, 1951); and Norman Kemp Smith, New Studies in the Philosophy of Descartes (London, 1952).

Specific aspects of Descartes’s scientific method are discussed in A. Gewirtz, “Experience and the Non-mathematical in the Cartesian Method,” in Journal of the History of Ideas, 2 (1941), 183–210; and A. C. Crombie,“Some Aspects of Descartes’ Attitude to Hypothesis and Experiment,” in Académie Internationale d’Histoire des Sciences, Actes du Symposium International des Sciences Physiques et Mathématiques dans la Première Moitié du XVII^e Siècle: Pise-Vinci, 16–18 Juin 1958 (Paris, 1960), pp. 192–201. An indispensable bibliography is G. Sebba, Descartes and His Philosophy: A Bibliographical Guide to the Literature, 1800–1958 (Athens, Ga., 1959).

A. C. Crombie

DESCARTES, RENE DU PERRON

(b. La Haye, Touraine, France, 31 March 1596;

d. Stockholm, Sweden, 11 February 1650), natural philosophy, scientific method, mathematics, optics, mechanics, physiology. For the original article on Descartes see DSB, vol. 4.

Since the 1970s there has been enormous interest in Descartes’s scientific thought. There have been numerous new studies of his physics and its foundations, and its relation to scholastic thought about the physical world. Recent studies have emphasized the systematic nature of Descartes’s scientific thought, and the way in which the various pieces of his thought fuse to make a unified whole. Also, as historians come to understand the period better, they have come to see what is distinctively Cartesian in this point of view, and how Descartes’s scientific thought differs radically from that of other contemporaries, such as Galileo.

Natural Philosophy . In both Le monde, ou Traité de la lumière (1630–1633) and the later and more formal Principia philosophiae (1644), Descartes put forward a genuine natural philosophy, as opposed to the kind of mixed mathematical investigations found in his Dioptrics or his mechanical writings. (See the treatment of those domains in “Descartes: Mathematics and Physics” in DSB vol. 4.) Central to this natural philosophy is a conception of a world created and sustained by God and governed by laws of nature. Indeed, Descartes was arguably the first to make the idea of a law of nature central to his conception of physics. This view, in turn, grounded a program for explaining the present state of the world by showing how it could be derived from an initial state, evolving in accordance with those laws of nature. In these respects, among others, Descartes’s program offers an interesting contrast to the very influential view of nature found in contemporaries such as Galileo.

There was a standard distinction between pure mathematics and mixed mathematics that dates far before the seventeenth century. Pure mathematics included geometry and arithmetic and was the pure study of mathematical objects such as geometrical objects and numbers. Mixed mathematics, however, included such domains as astronomy, optics, music, mechanics, and, by the seventeenth century, motion. Mixed mathematics was mathematical insofar as it treated its subjects with the tools of mathematics, but it differed from pure mathematics insofar as it applied to the physical world. It also differed from physics or natural philosophy, terms generally synonymous in the period. For an Aristotelian physicist, natural philosophy was limited to the natural world, the world of things with natures, such as the Aristotelian elements (fire, air, water, and earth), living things, and appropriate mixtures. This differs from the mixed mathematical science of mechanics, which treats machines, which are artificial and have no nature properly speaking. For Descartes and some of his contemporaries, though, the distinction between the natural and the artificial had been broken down, thus making this distinction between mixed mathematics and natural philosophy irrelevant. (See the treatment of this issue in “Descartes” in DSB vol. 4.) However, natural philosophy was also distinguished from the mixed mathematical sciences by virtue of the fact that in natural philosophy, one dealt with the true causes and explanations of things, and not just their mathematical descriptions at least in principle.

Descartes worked on both sides of the divide. His Dioptrics (1637) and essay on mechanics (Explication des engins par l’aide desquels on peut avec une petite force lever un fardeau fort pesant of 1637) can be read as essays in mixed mathematics, though even in these texts Descartes shows his interest in understanding the true cause of the phenomena. But in Le monde (1630–1633) and more especially in the Principia philosophiae (1644) his goal was a complete natural philosophy, beginning with first principles and deriving a complete account of the world from them.

At the bottom level are the first principles, what he called his first philosophy or his metaphysics. These included the existence and nature of the soul or mind (the first thing we come upon when we philosophize in order), followed by God, and finally the existence and nature of matter or body. These are treated in part I and the beginning of part II of the Principia philosophiae, though they are treated at greater length in the Meditations (1641). (These were discussed less systematically in Le monde, though they did enter into the details of the arguments.) Whereas the soul would enter into his account of the human being, it is God and the nature of body that were most at issue in his account of the physical world.

Descartes argued that the nature of body was to be extended. For him that meant that in the strictest sense bodies had geometrical properties and nothing else: Bodies were the objects of geometry made real, and nothing else. And so, apparent properties of bodies such as hot or cold, wet or dry (to take the Aristotelian primary qualities), or color, are just sensations in the mind, grounded in the size, shape and motion of the smaller parts that make up bodies. It also follows from this conception that bodies have no inherent tendency to move in any particular direction. The natural tendency fire has to rise or earth to fall must be explained, again, in terms of the size, shape and motion of the parts that make up the bodies in question, as they interact with the other bodies in their environment. Another consequence of this conception of body is that there is no empty space. Any volume constitutes an extension, and because one cannot have an extension without a substance in which it inheres, Descartes argued that any volume will be an extended substance and therefore a body. For that reason Descartes did not recognize space as something over and above body: To talk about space is just to talk about bodies in an abstract way. To say that a body D can occupy the same space that is now occupied by a body C is to say that it could happen that D hold the same relation to some other bodies A and B that C now bears to those bodies. And because all space is occupied, even though the universe as a whole is infinite, Descartes argued that all motion is ultimately circular, as bodies move out of the way of other bodies in order to make way for the other bodies to enter the spaces where they had formerly been.

Laws of Motion . Motion can be defined in terms of the relation of bodies to one another. However, to understand the laws of motion, Descartes turned to the general cause of motion, God. Whereas the laws of nature (laws of motion) are first introduced in chapter 7 of Le monde, the most systematic presentation was later in the Principia philosophiae. The discussion there began with a characterization of God as the “universal and primary cause [of motion], which is the general cause of all motions which are in the world” (Principia part II § 36). God’s activity in sustaining the world from moment to moment gives rise to an important general rule: “from the sole fact that God moved the parts of matter when he first created them, and now conserves matter as a whole in the same way and with the same order with which he first created it, it is most consistent with reason that we think that he always conserves the same amount of motion in it” (Principia part II § 36). This amount is what he called quantity of motion, the sum of the size times the speed of the particles that make up the universe. (Note here that this is not what later came to be called momentum. Directionality, what Descartes called determination is not governed by this law, only speed, a scalar quantity.)

Descartes did not identify this general conservation law as a law. It is a very general constraint that governs the universe as a whole, and did not say anything about the behavior of particular bodies. For that reason, in the following sections Descartes introduced three specific constraints, each of which was explicitly identified as a law of nature(lex naturae). The first law is that “each and every thing, insofar as it can [quantum in se est] perseveres in the same state, nor is it ever moved unless by an external cause.” More specifically, Descartes inferred from this that “what is once moved, always proceeds to move” (Principia part II § 37). This is a law of the persistence of motion in an individual body, understood as a special case of the persistence of any property bodies have. The second reads: “every motion in itself is straight and therefore that which moves circularly always tends to recede from the center of the circle which it describes” (Principia part II § 39). This is a law of the persistence of directionality in an individual body. These two laws are often regarded as Descartes’s law of inertia, connecting them to Newton’s first law of motion. But this is misleading. For Descartes and his contemporaries, inertia was the property bodies have by virtue of which they tend to come to rest. For Descartes these laws dealt with the property bodies have by virtue of which they remain in rectilinear motion. The third law governs the collision of bodies:

When a moving body comes upon another, if it has less force for proceeding in a straight line than the other has to resist it, then it is deflected in another direction, and retaining its motion, changes only its determination. But if it has more, then it moves the other body with it, and gives the other as much of its motion as it itself loses. (Principles, part II, § 40)

Unlike the conservation principle and the first two laws, all of which deal with the persistence of certain features of bodies, this law can be thought of as reconciling the behavior of two bodies whose motion and direction would tend to be conserved, but because of the impenetrability of bodies, cannot. Descartes followed this with seven rules of impact, showing how the third law can be applied to the case of direct collision under certain assumptions, such as that the bodies are perfectly hard and isolated from all other bodies. In the examples Descartes made it clear how collisions are meant to be governed by his general conservation principle, and how he thought the forces involved are to be calculated. Descartes’s collision rule turned out to be very problematic. It is not at all clear what exactly he meant by force in the law, and how bodies that contain only extension can have either a force for proceeding or a force of resistance. The rules of impact drew serious criticisms from a number of later people, most notably Christiaan Huygens and Gottfried W. von Leibniz, who showed that they are inconsistent with a relativistic conception of motion and with certain plausible wider constraints that one might want to impose on a scientific theory.

Even though the laws were somewhat suspicious, particularly the collision law and the rules of impact that are connected with it, the overall view of natural philosophy and the physical world were important and influential. What Descartes offered was a conception of a world governed by laws of nature, grounded in God. Even though Descartes himself did not present them in mathematical form, because they could in principle be given in terms of size, shape, and motion, it was a conception of a law-governed universe that was well-suited to a mathematical physics. Another important feature of the view was that the basic laws are understood in terms of the conservation of certain features of bodies. This conception of physics would characterize the conception of physics found later in Leibniz’s system.

Structure of the World . With these laws in place, Descartes then proceeded to account for the current state of the world in outline. He began with an hypothesis about the initial state of the world, an assumption of random sized initial bodies in chapter 6 of Le monde and of uniform sided initial bodies in Principia part III § 46. He then showed how from this initial state and the laws of nature, these initial bodies would divide themselves into bodies of three different sizes, which he called elements. Because the world is a plenum, and all motion circular, the universe will become divided into an infinity of vortices of fluid matter, each with a sun (or star) at the center which will be the source of light, understood as centrifugal pressure in the vortex. In Le monde(chapter 9) the larger masses of matter from the initial creation form planets and comets, the former staying within a single vortex and rotating around its sun, the latter migrating from one vortex to another, moving at the interstices between vortices. In part III of the Principia philosophiae, Descartes argued that these larger masses are formed from suns (stars) which become encrusted with sunspots, and are either captured by vortices (and become planets) or wander from one vortex to another (and become comets).

In part four of the Principia Descartes dealt with the structure of the Earth in some detail. Descartes argued that the Earth has three regions. Because it originated as a star, encrusted by sunspots, it still retains at its center the same celestial matter found in other stars. Above that is the dense and opaque material that derives from the sunspots that encrusted the original star. The top layer is a mixture of different elements, resulting from the interaction between the second layer and the particles in the vortex surrounding the Earth. All the bodies in human experience are made up of the parts of this third layer. Such terrestrial bodies are not heavy in themselves, but only because they are driven toward the center of the Earth by the heavenly matter that surrounds the Earth and forms a vortex around it. Descartes went on to deal with a wide variety of terrestrial phenomena, including the formation of mountains and valleys, the nature of the air, oceans and their tides, the properties of various chemicals and metals and why they are found where they are in the Earth, the properties of fire and how it is generated, and the properties of glass. The account of the bodies found on Earth ends with a lengthy account of the magnet, giving an ingenious mechanistic model that attempts to unify a wide variety of empirical data about the behavior of magnets by way of a few simple hypotheses.

The main body of the Principia ends with terrestrial physics. However, Descartes had intended to end with an account of living things, derived in the same way that he attempted to derive the properties of the Earth, arguing genetically from some initial assumptions and the laws of nature, in a broadly evolutionary fashion. Descartes was working on these issues in his last years, though never fully integrated his account of the life sciences into his natural philosophy. (See the treatment of Descartes’s work in the life sciences in “Descartes: Physiology” in DSB vol. 4.)

Contrast with Galileo . Though often paired with Galileo as one of the founding fathers of the New Science of the seventeenth century, Descartes actually saw himself as doing something radically different. In a letter to Marin Mersenne from 11 October 1638, Descartes conveyed his comments on Galileo’s program, with particular reference to the Discorsi (1637). He wrote:

I find in general that he philosophizes much better than is common, insofar as he avoids as much as he can the errors of the schools, and tries to examine physical matters using mathematical reasons. In that I am entirely in agreement with him.… But it seems to me that he is greatly lacking insofar as he continually makes digressions and never stops to explain a matter in its entirety. This shows that he hasent examined them in arder, and without having considered the first causes of nature, he has only looked for the reasons for certain particular effects, and thus that he has built without a foundation.

This nicely captures the spirit of the natural philosophical approach that Descartes took in contrast to the mixed mathematical approach that he saw in Galileo. For Descartes, what was important was bringing the explanation of phenomena back to their ultimate causes, building a science grounded in first principles. When possible, he was happy to derive mathematically rigorous representations of nature, like Galileo, as he did, for example, with the sine law of refraction. (See the treatment of refraction in “Descartes: Mathematics and Physics” in the original DSB). But for Descartes, the mathematical expressions were empty unless accompanied by an account of the true causes.

SUPPLEMENTARY BIBLIOGRAPHY

WORKS BY DESCARTES

Regulae ad directionem ingenii. Edited by Giovanni Crapulli. Gravenhage, Netherlands: Martinus Nijhoff, 1966. This is a scholarly edition of the text.

Régles utiles et claires pour la direction de l’esprit en la recherche de la vérité. Edited and translated by Jean-Luc Marion and Pierre Costabel. The Hague: Martinus Nijhoff, 1977. This is a translation of the Regulae with an extensive commentary on the scientific themes.

Ecrits physiologiques et médicaux. Edited by Vincent Aucante. Paris: Presses Universitaires de France, 2000.

Tutte le lettere 1619–1650. Edited by Giulia Belgioioso et al. Milan: Bompiani, 2005. This is a new edition of all Descartes’s correspondence, in original language with Italian translation and excellent notes on the scientific and mathematical letters.

OTHER SOURCES

Aiton, Eric J. The Vortex Theory of Planetary Motions. London: Macdonald, 1972.

Ariew, Roger. Descartes and the Last Scholastics. Ithaca, NY: Cornell University Press, 1999.

Armogathe, Jean Robert, and Giulia Belgioioso. Descartes, Principia Philosophiae: 1644–1994: Atti del convegno per il 350^o anniversario della pubblicazione dell’opera. Naples, Italy: Vivarium, 1996. This is a major collection of writings on Descartes’s scientific work from a conference given on the anniversary of the publication of the Principia.

———, and Vincent Carraud. Bibliographie Cartésienne : 1960–1996. Lecce, Italy: Conte Editore, 2003.

Aucante, Vincent. La philosophie médicale de Descartes. Paris: Presses Universitaires de France, 2006.

Belgioioso, Giulia, ed., et al. Descartes, Il Metodo e I Saggi : Atti del convegno per il 350^o anniversario della pubblicazione del Discours de la méthode e degli Essais. Rome: Istituto della enciclopedia italiana, 1990. This is a major collection of writings on Descartes’s scientific work from a conference given on the anniversary of the publication of the Discourse and Essays.

Clarke, Desmond M. Descartes: A Biography. Cambridge, U.K.: Cambridge University Press, 2006.

Des Chene, Dennis. Physiologia: Natural Philosophy in Late Aristotelian and Cartesian Thought. Ithaca, NY: Cornell University Press, 1996.

———. Spirits and Clocks: Machine and Organism in Descartes. Ithaca, NY: Cornell University Press, 2001.

Duchesneau, François. Les modèles du vivant de Descartes à Leibniz. Paris: J. Vrin, 1998.

Garber, Daniel. Descartes’ Metaphysical Physics, Science and Its Conceptual Foundations. Chicago: University of Chicago Press, 1992.

Gaukroger, Stephen. Descartes: Philosophy, Mathematics and Physics. Sussex and Totowa, N.J.: Harvester Press and Barnes and Noble Books, 1980. This is an important collection that contains a number of essays that have become classics, including essays by John Schuster, Michael Mahoney, Martial Gueroult, and Alan Gabbey.

———. Descartes: An Intellectual Biography. Oxford: Oxford University Press, 1995.

———, John Schuster, and John Sutton. Descartes’ Natural Philosophy, Routledge Studies in Seventeenth-Century Philosophy. London: Routledge, 2000. This is a large collection of late twentieth century studies focused on Descartes’s science.

———. Descartes’ System of Natural Philosophy. Cambridge, U.K.: Cambridge University Press, 2002.

Daniel Garber

René Descartes

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). 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). □