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History of Philosophy
by Turner, William (S.T.D.)

Life. René Descartes was born at La Haye, in Touraine, in the year 1596. He studied at the Jesuit college of La Flèche, and throughout his life maintained the most friendly relations with his teachers, his greatest regret being their refusal to accept his philosophy. On quitting the college of La Flèche (1612) he went to Paris, where for a time he abandoned all serious study; later, however, in obedience to the maxim Bene vixit qui bene latuit, which he made the guiding principle of his life, he retired into seclusion in a lonely quarter of the city, and there continued his studies. In 1617, determined to study the great book of the world, he took service as a volunteer in the army of Prince Maurice of Nassau, repairing first to Holland, and afterwards to Germany, where he left the army of Prince Maurice for that of the Elector of Bavaria. While in winter quarters at Neuburg on the Danube, in 1619-1620, he experienced the mental crisis of his life, and discovered, as he tells us, "the foundations of a wonderful science" -- the principle, namely, that all geometrical problems may be solved by algebraical symbols. It was in this same mental crisis that the notion of universal methodic doubt first occurred to him, as well as the thought that "the mysteries of Nature and the laws of Mathematics could both be unlocked by the same key." [1] After a brief visit to his native place, he took up his abode in Holland in 1629, and there published his most important philosophical works, the Discours de la méthode (1637), Meditationes de Prima Philosophia (1641), and Principia Philosophiae (1644). At the invitation of Queen Christina of Sweden, he went to Stockholm in 1649, where he died in the early part of the following year.
[1] "In otiis hibernis naturae mysteria componens cum legibus matheseos, utriusque arcana eadem clave reserari posse ausus est sperare." Epitaph composed by Chanut.
Sources. Besides the works mentioned in the preceding paragraph, Descartes wrote a Traité des passions de l'âme published in 1650. Among his posthumous works the most important are the Recherche de la vérité and Règles pour la direction de l'esprit, published in 1701. His Letters (published 1657-1667) are important for the understanding of his doctrines. The collected works of Descartes were published in 1650 and 1701. Cousin's edition (11 vols., Paris, 1824-1826) has long been the standard edition. It will doubtless be superseded by the edition which is being prepared by Messrs. Adam and Tannery, and of which three volumes have already (1901) appeared. With regard to secondary sources, it is impossible to give here an adequate list. Mahaffy's Descartes, included in Blackwood's Philosophical Classics (Edinburgh and Philadelphia, 1894), is an excellent manual for English students of Descartes. [2]
[2] Consult Bonillier, Histoire de la philosophie cartisienne (troisième édition, Paris, 1868); also Wallace, article on "Descartes" in Encyclopaedia Britannica. Translations: Method, Meditations, etc., by Veitch (tenth edition, London, 1890); Meditations, by Lowndes (London, 1878); Extracts, by Torrey (New York, 1892).

Physical and Mathematical Doctrines. Descartes' contributions to the mathematical and physical sciences, important as they are, cannot be treated here except in a general way. Descartes is the founder of analytical geometry; to the science of algebra he contributed the treatment of negative roots and the invention of the system of index notation; to physics he contributed the first statement of the "law of sines" in reference to the refraction of light. This last point is, however, a matter of dispute, the discovery being by some authorities attributed to Snellius. [3]
[3] Cf. Revue de métaphysique et de morale, Juillet, 1896.
Descartes' Method. Descartes, as is well known, advocates universal methodic doubt as the beginning of philosophical thinking. During his sojourn at Neuburg, to which allusion has already been made, he occupied himself with the project of finding some one certain truth and of discovering "the true method of attaining to the knowledge of all things of which his mind was capable." With this purpose in view he first resolved to get rid of all prejudices acquired from books, and to call in question all the principles and conclusions of science and philosophy. It is to be remarked that Descartes did not propose this method of doubt as a means to be used indiscriminately by all; the resolution which he made was merely for his personal use. It is to be noted, in the second place, that Descartes excepted from his universal doubt truths belonging to theology and to the political and moral sciences. Having resolved, then, to doubt everything that his predecessors had taught, he proceeded to draw up a set of rules for his further guidance. The logic of the schools, he remarked, will be of little avail in this systematic inquiry, because it is suited rather to the communication than to the discovery of truth. Accordingly, he proposed to substitute for the rules of formal logic the four following principles: (1) To admit nothing as true which is not perceived so clearly and distinctly as to admit of no doubt; (2) to divide, as far as possible, every question into its natural parts; (3) to pass (synthetically) from the easier to the more difficult; (4) to make accurate and complete enumerations, both in seeking middle terms and in considering the elements of difficult problems. [4]
[4] Cf. Discours de la méthode, IIme partie (OEuvres choisies, p. 14).
These simple and elementary rules are not difficult of observance. They indicate (and this is the point with which we are chiefly concerned) the essentially deductive nature of the method which Descartes introduced. Indeed, during the winter of 1619-1620, when Descartes started out to construct a system of knowledge by the aid of these rules, he first applied them to the mathematical sciences, but finding the method to be at once easy and fertile of results, and considering that the principles of all sciences are derived from first philosophy, he determined to apply to all branches of physical and philosophical science the method which he had so successfully used in mathematical studies. Descartes' own statements preclude all possible doubt as to the deductive nature of his philosophical and scientific method:
Toute ma physique n'est autre chose que géométrie, les
mathematiques sont les principaux fondements sur lesquels j'appuie tous
mes raisonnements. . . . apud me omnia sunt mathematica in
natura. [5]
[5] Cf. Lettres, in Cousin's edition of Descartes' Works, VII, 121, and Règles, etc., passim.
Starting Point. The plan conceived during the winter of 1619-1620 -- that, namely, of applying to all branches of knowledge the mathematical method, which starts from an intuition and proceeds by deduction -- was perfected in the Discourse on Method, which appeared in 1637, and in the Meditations, published in 1641. In these treatises Descartes attempts to discover an incontrovertible truth (aliquid inconcussum), known to us by a clear and distinct intuition, and from that single truth to deduce all science. The truth which he discovers to be beyond all possibility of doubt, and which he accordingly selects as the beginning of all scientific knowledge, is the fact of his own conscious thought. I may doubt, he observes, about everything else, but I cannot doubt that I think, for to doubt is to think. But if I think, I exist; "Cogito, ergo sum." [6]
[6] Cf. Discours, IVme partie (OEuvres choisies, p. 25); also IIme Méditation, op. cit., p. 79.
To this Gassendi objected that one may infer existence from any external action, such as walking, and argue Ambulo, ergo sum. But Descartes protested that the ergo sum is not an inference, as indeed it cannot be if Cogito is the first truth; it is, however, evident that Descartes himself, by the use of the word ergo, gave rise to the misunderstanding. The complex proposition, therefore, "Cogito, ergo sum," merely expresses the undeniable certainty of the self-evident intuition that I think, and of the equally self-evident intuition that I exist. No doubt Descartes selected thought rather than an external action, such as walking, because, though I may be deceived as to whether I am walking or not, I cannot be deceived as to whether I am thinking. He felt, too, that thought in some way implies existence, and he had, perhaps, in mind St. Augustine's Quod si fallor, sum; he does not, however, appear to have realized the difference between an indirect argument such as St. Augustine's was -- merely a reductio ad absurdum of an opponent's contention -- and a direct proof or demonstration.

Descartes might have turned, at this point, to the consideration of matter or extension; he might have considered that we have a clear and distinct idea of extension, which is as primitive and underived as is our idea of thought and thinking-subject; but instead of doing this he proceeded, like the mathematician that he was, to deduce all knowable truth from the fewest possible premises. He passed, therefore, deductively, from his own existence to the existence of God, and from the existence of God to the existence of extended matter (external world).

The Existence of God. Descartes reduces his proofs of the existence of God to two: [7] the a posteriori argument from effect to cause, and the a priori argument, which proceeds from the idea of God to the existence of God. We take up first the a posteriori argument.
[7] Cf. Réponses aux premières objections, op. cit., p. 146. Elsewhere (OEuvres, ed. Cousin, IX, 164) Descartes enumerates three proofs.
Having established the truth that I think and that therefore I exist, Descartes goes on, in the Third Meditation, to argue deductively as follows: Of the ideas which I find in my mind, some arise from external causes, and others from the mind itself. Now, among the ideas which I possess is the idea of God, that is, the idea of a most perfect Being. This idea, however, cannot have been produced by me; for the fact that I doubt proves that I am an imperfect being, and an imperfect being cannot cause that which is most perfect. He alone Who is Himself endowed with all perfection can produce in my mind the idea of a most perfect Being. Therefore, from the idea of God which I possess, I am warranted in concluding that God exists. [8]
[8] OEuvres choisies, p. 103.
The existence of God is, then, not an intuitive truth, but rather a truth inferred from an intuition of the contents of the mind. The most serious flaw in Descartes' a posteriori argument is the assumption of the principle of causality. Descartes, it must be remembered, has resolved to doubt about everything, and up to this point he has established merely the truth that he thinks and that he exists. He has no right, therefore, to assume the principle of causality, in virtue of which it is affirmed that whatever perfection is in the effect must be also in the cause. If he assumes it in virtue of clear and distinct perception, he must abandon the attempt to deduce all truth from one intuition. Apart from this flaw, which may be called accidental, the argument is intrinsically invalid. It is not true that an idea cannot contain representatively a perfection which is neither formally nor eminently in the mind that conceives the idea. I may form in my mind an idea of the Infinite without possessing the perfections which the idea of the Infinite represents. The principle that the effect is not greater than the sum of its causes, is true in the order of being; but in the argument which we are studying, the effect is in the order of representation, while the cause is in the order of existence, and the transition from the ideal order to the real order is always fallacious.

We next come to the a priori, or, as Descartes calls it, the geometrical proof of the existence of God. We find in our minds certain ideas possessing properties so fixed and immutable that we cannot acquire such ideas without holding to the truth of the properties which are necessarily connected with them. We cannot, for example, possess the idea of a triangle, and understand what the idea means, without admitting that the sum of the angles of a triangle is equal to two right angles. Now, when we examine the idea of God we find that it is the idea of the most perfect Being, an idea, namely, which comprises all perfections, including that of existence. If existence were not comprised among the perfections of God, He would not be the most perfect Being. Therefore, from the fact that we possess the idea of a supremely perfect Being we are warranted in concluding that such a Being exists. The argument may be stated in Scholastic form and phraseology thus:
Ens, de cujus essentia est existentia, necessario existit: Atqui Deus
est ens de cujus essentia est existentia; ergo Deus necessario
existit. [9]
[9] Cf. Revue de métaphysique et de morale, Juillet, 1896, p. 436. The argument is found in the Vme Méd., Oeuvres Choisies, p. 120.
Descartes' geometrical or ontological argument raised a perfect tempest of controversy. It was attacked on all sides as being a mere restatement of St. Anselm's argument, as containing an illogical transition from the ideal to the real order, and as falsely assuming that existence is a perfection. Despite these objections, the argument gained many supporters, and remained in honor among the Cartesians of the seventeenth and eighteenth centuries.

Having thus demonstrated the existence of God, Descartes next proceeds to infer from the goodness and wisdom of God the veracity of the faculties of the human mind, and to build on this basis the whole superstructure of philosophy. The circulus vitiosus is flagrant: Descartes proves the existence of God and then from the veracity of God infers the reliableness of the cognitive powers by which the existence of God has been established.

If, Descartes proceeds to argue, our faculties of knowledge are reliable, our senses are to be believed when they testify to the existence of the external world. The existence of material extended being is not known therefore by intuition, but rather by way of inference from the primitive intuition of my own existence and from the truths deduced therefrom.

Doctrine of Two Substances. By direct intuition, then, we know that there is a thinking substance, self, and by inference we know that there is an extended substance, matter. Now, substance being that which so exists as to need nothing else for its existence (res quae ita existit ut nulla alia re indigeat ad existendum), it is clear that God alone is, properly and strictly speaking, a substance. Mind, however, and matter, since they need nothing for their existence except the cooperation of God, may be called created substances. The essence of mind is thought; the essence of matter is extension. Everything that may be predicated of mind is a mode of thought, while everything that may be predicated of matter is a mode of extension. Mind and matter, therefore, are antithetical. [10] It remains to see how Descartes applied this doctrine of dualism to his concept of nature and to anthropology. But before taking up Descartes' philosophy of nature, it will be convenient to gather from the foregoing doctrines the principles of Descartes' epistemology.
[10] Cf. VIme Méd., op. cit., p. 126.
Descartes' Epistemology. When Descartes makes the veracity of God the all-sufficient guarantee for the reliability of our sense processes and of our thought processes, he lays down a principle which he wishes to be regarded as the ultimate metaphysical basis of certitude. But in every system of epistemology principles of psychology are implied, and we may ask, for example, by what quality is the knowledge which comes from the outside world to be distinguished from the knowledge which comes from the world within us? How can I distinguish the idea of a thing from the idea of a mere mental fancy? How, for instance, does my idea of Julius Caesar differ from my idea of Aladdin? Descartes would answer that the mind, being a res cogitans, a substance whose very essence is thought, must be conscious of all its acts. When, therefore, I am conscious of an idea which I myself formed (idea a meipsofacta) I am conscious of having formed it; but when an idea comes to me from outside (idea adventitia), I am conscious of the non-interference of my will, and I know that, whether I will it or not, the idea represents so much and no more. Ideas of this latter class must, therefore, be caused by something outside the mind, and I conclude that the something-outside-the-mind exists. Descartes is, then, a reasoned realist.

Descartes maintains the existence of real substance as well as of real qualities; for, if qualities exist, substances exist, since nothing can have no qualities (Nihili nulla sunt attributa). Thus in the Principia Philosophiae [11] he writes: "Ex hoc quod aliquod attributum adesse percipiamus concludimus aliquam adesse rem existentem sive substantiam cui illud tribui possit." Still, he teaches that the secondary qualities, taste, color, etc., of material things, are modes of consciousness rather than qualities of real substances. There are, indeed, movements of real substances, which movements, on being communicated to the nerves or filaments, are conducted to the pineal gland, where they come in contact with the mind and are perceived by it. It is not, however, the movement of the substance in the world outside us that is perceived by the mind, but merely the movement of the filaments, which is caused by the movement of the external substance. There is, then, a real cause of color, taste, etc.; nevertheless, color, taste, etc., being only modes of the subjective organism, are, strictly speaking, states of self rather than states of not-self. By this doctrine of subjectivism Descartes paved the way for the idealism of subsequent philosophers. It was easy for Berkeley, for example, to reason away the primary qualities of matter by reducing them, as Descartes had reduced the secondary qualities, to states of self, and to conclude that the very substance of matter has no existence except in thought. Descartes, it must be remembered, is not an idealist; he maintains the existence of an external world of matter with its qualities, extension and motion; nevertheless, he is justly regarded as the founder of modern idealism.
[11] II, 52.
Philosophy of Nature. What is the essence of material substance? Descartes, as we have seen, answered that it is extension. The secondary qualities are merely states of the perceiving mind, and among the primary qualities extension alone is so essential to matter that without it matter is unthinkable. Now, from extension proceed the divisibility, figurability, and mobility of matter. Of course, the principle that matter is nothing but extension would, if pushed to its logical conclusions, lead to subjectivism. Descartes taught, as is well known, that the essences of things depend on the will of God. Now, the Divine Will is immutable; matter, having at its creation been endowed with a certain measure of motion and rest, retains this measure unchanged. 12] Hence the laws of motion: Everything tends to continue in the state of rest or of motion in which it is, and changes that state only as a result of the interference of some extraneous cause. Thus Descartes' notion of matter harmonized with subsequent discoveries. He himself inferred from his notion of matter the homogeneousness of space, the existence of substance in the interstellar spaces, the formation of the universe from a primitively homogeneous mass, the explanation of the distinction between solid and fluid bodies, and so forth. The only thing that extension confers on matter is mobility; matter is essentially inert, and receives its motion from the first efficient cause.
[12] Op. cit., III, 47.
Descartes devotes special attention to the application of his mechanical concept of nature to dioptrics. He discards the entire Scholastic system of forms, accidental and substantial, entitative (accounting for the qualities of things) and representative (accounting for our knowledge of things), and explains the phenomena of light, color, vision, and so forth in terms of motion. All sensations, he teaches, including that of light, are accounted for by the motion of particles; light itself is a motion -- not, indeed, a vibration (Descartes did not advance so far as this) but a horizontal pushing of one particle by another. It is needless to remark that, long before the days of Descartes, Aristotle denied the emission theory of light and held that light is a mode of motion. Descartes, however, advanced beyond all his predecessors when he taught [13] that the difference of one color from another is due to the varying velocities with which the motions of light reach the eye. Not less interesting is the portion of the Dioptric (Sixth Discourse) in which he anticipates many of Berkeley's contributions to the theory of vision.
[13] Météores, VIIIme Discours.
Psychology. It is in Descartes' psychology that the disastrous consequences of his doctrine of the two substances appear. If mind and matter are so opposed as to have nothing in common, the union of soul and body in man must be merely a mechanical one. The body, Descartes teaches, is a machine, so constructed that it carries on its own operations by virtue of the impulse received from the soul, which Descartes locates in the pineal gland. This portion of the brain is selected as the seat of the soul because it is the only part of the cerebral substance which is not double, and it is evident, Descartes observes, that if the organ of the soul were double, we should perceive two objects instead of one.

It is important to note that Descartes attaches to the word mind a meaning which is at once narrower than that of the word soul and wider than that of the expression thinking faculty. He defines mind as res cogitans; but he includes under the term thought sensation, imagination, and volition as well as the processes of ideation; thought, in fact, he makes synonymous with states of consciousness. Thought, however, does not include all the vital functions. [14]
[14] Principia Philosophiae, I, 9.
In his account of the physiological processes of the body, as well as in his doctrine regarding sensation, Descartes has recourse to the theory of animal spirits. The only physiological principles which he admits are motion and warmth. God, he observes, has placed in the hearts of men and animals a vital warmth which promotes the circulation of the blood [15] and separates from the blood its finest and most mobile particles, which constitute the animal spirits (spiritus animales). This fluid ("very subtle wind," as he sometimes calls it) conveys the stimulation of the senses to the pineal gland, and, returning through the nerves to the muscles, conveys the impulse of motion from the pineal gland to the limbs. In animals there is no conscious sensation but only this automatic response of the animal mechanism to stimuli; so that when an animal on the dissecting table utters what is apparently a cry of pain, the noise is, as the Cartesian vivisectionists contended, merely the crash of broken machinery. In man, however, the motion of the animal spirits, on reaching the pineal gland, enters into the region of thought, and thus there arises a passio. In the same way, the motion imparted by the mind from the pineal gland leaves the region of thought and is an actio. Hence, the contents of the human mind (cogitationes) are divided into actiones and passiones. Descartes, however, does not maintain this distinction in the details of his account of the contents of the human mind.
[15] Descartes mentions in terms of praise Harvey's De Motu Cordis et Sanguinis in Animalibus (1628).
With regard to the origin of ideas, Descartes at one time held a threefold classification of ideas, namely innatae, adventitiae, and a meipsofactae. He saw fit, however, at a later period, to explain that by innate ideas he meant merely natural dispositions of the mind which enable it to develop certain ideas. "In the same sense," he observes in his answer to Regius, [16] "we say that certain illnesses are innate in certain families, by which we mean merely that children are born with a disposition for developing those illnesses." None of our ideas, therefore, are actually innate. All our ideas are either occasioned by our sensations, that is, they come, apparently at least, from the world outside and are therefore called adventitiae, or result from voluntary combinations of elements of thought, and hence are called ideae a meipso factae. Besides these two classes, we must distinguish the innate dispositions to develop certain ideas, and these dispositions we may describe as innate potencies of ideas.
[16] Cousin's edition, X, 70.
Descartes contrasts will with mind. The mind is essentially limited, while the will is unlimited. We are directly and immediately conscious of our power to perform or to omit certain actions, and in this power freedom consists. [17] From the freedom of will comes the power of choosing to assert that which we do not understand. The will is, therefore, the source of error.
[17] IVme Méd.
The passions of the soul form, as we have seen, the subject of a special treatise by Descartes. Passion, like every other state of consciousness, is a thought: it is not a state of the body, for every state of the body is either a figure or a movement. Still it is occasioned by the body, for it arises in the following manner. When an impression is conveyed to the brain, the animal spirits are disturbed and the commotion thus produced results in approach or flight or attitude of defense. Now, in the lower animals, this is all that takes place. But in the case of man, the mind perceives this commotion of the animal spirits, and the thought of the commotion is emotion, or passion. Passion, therefore, is a specifically human phenomenon. [18] According to Descartes; the primitive emotions are six in number: admiratio, amor, odium, cupiditas (désir), gaudium, and tristitia.
[18] Cf. Mahaffy, Descartes, p. 184.
The consideration of the emotions leads us to the next and last division of Descartes' philosophy, namely, his ethical doctrines.

Ethical Doctrines. Descartes did not attempt to elaborate a system of ethics from the principles of his speculative philosophy. In his Letters, and especially in those addressed to Princess Elizabeth, daughter of Frederick V of the Palatinate, and in those written to Queen Christina, he lays down certain ethical principles which betray the influence of the Stoics. The highest happiness, he teaches, is to be attained by striving for a knowledge of what is right and by cultivating the will in order to strengthen it in its resolve to do what is right. Knowledge of God as the author of all things, knowledge of the universe as infinite in magnitude, knowledge of the soul as distinct from the body, and knowledge of self as part of the domestic and civil society, -- these are the greatest aids to the attainment of virtue and happiness. We should realize the unlimited power of the will; for from this feeling of power springs the virtue of magnanimity, which is the foundation of all other virtues. [19]
[19] Cf. Höffding, Hist. of Mod. Phil., I, 240, 241.
Historical Position. Descartes exercised a profound influence on his own and subsequent generations. He stirred the thinking world of his time to its very depths. His doctrines left their impress on the theology, science, and literature, as well as on the philosophy of the seventeenth century. His philosophy was adopted and defended by religious orders. He had for patron the Prince of Condé, the ablest general of the age, and such was the greatness of his fame that more than one royal personage sought admission to the ranks of his pupils. All this enthusiasm produced, however, a natural reaction against his teachings. His works were placed on the Index donec corrigantur (November 20, 1663), the Calvinist universities in Holland proscribed his writings, and the University of Oxford forbade the teaching of his philosophy. [20] But in spite of all opposition, Descartes' influence continued, and it is hardly an exaggeration to say that his thought determined the whole course of the development of modern philosophy.
[20] Cf. González, op. cit., III, 239.
Descartes' philosophy is original in form rather than in content. His most noteworthy contribution to philosophy is his method. This method is, as we have seen, essentially mathematical, the very opposite of what is known as the scientific method. Yet, by a strange irony of fate, physical science owes more to Descartes than to Bacon, who sought to reform the sciences by the introduction of the inductive in lieu of the syllogistic process.

Descartes has been compared to Socrates, and indeed he is, in a sense, the Socrates of modern thought. He called attention, as Socrates had done, to the necessity of studying the nature of thought and the conditions of knowledge. But, unfortunately for the subsequent development of philosophy, he did not base his system of psychology on experience. All his psychological inquiry was vitiated by his preconceived doctrine of the absolute antithesis of mind and matter, a doctrine which, by creating an imaginary chasm between subject and object, undid all that Socrates, Aristotle, and the schoolmen had accomplished. This doctrine is the luckless legacy of Cartesianism to modern thought, for "how to bridge the (imaginary) chasm between mind and matter" came to be the problem which almost every great philosopher since Descartes' time has striven in vain to solve.

From this fundamental misconception of the relation between mind and matter followed a complete misunderstanding of the purpose of philosophical inquiry. After Descartes, philosophy once more becomes anthropocentric, -- it reduces itself to the study of individual consciousness, to a geometry of deductions from internal experience; and the objective world, its origin, plan, and destiny, the place of man in nature, and even the existence of an intelligent first cause, are all made secondary subjects of inquiry, to be decided according to the result of the study of our own consciousness. This inversion of the natural perspective is what a modern writer has characterized as the "topsy-turveydom of Cartesianism."

To Descartes, too, may be traced the misunderstanding which prevails between those who believe in the spirituality of the human soul and those who rightly insist on the value of experimental methods in the study of psychic phenomena. For the concrete dualistic spiritualism of Aristotle and the schoolmen Descartes substituted the absolute dualistic spiritualism of Plato, thereby establishing at the outset of the modern period an altogether unnecessary antagonism between spiritualism and empiricism -- an antagonism which eventually drove the empirical psychologist to adopt the materialistic concept of the soul as the only concept which justified the study of the correlation between psychic phenomena and physiological processes.


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