This part of his theory was abandoned by his school—first by his Dutch disciple Geulincx, and later by Malebranche and Spinoza. The physicists discovered the conservation of momentum, according to which the total quantity of motion in the world in any given direction is constant. This showed that the sort of action of mind on matter that Descartes imagined is impossible. Assuming—as was very generally assumed in the Cartesian school—that all physical action is of the nature of impact, dynamical laws suffice to determine the motions of matter, and there is no room for any influence of mind. But this raises a difficulty. My arm moves when I will that it shall move, but my will is a mental phenomenon and the motion of my arm a physical phenomenon. Why then, if mind and matter cannot interact, does my body behave as if my mind controlled it? To this Geulincx invented an answer, known as the theory of the “two clocks.” Suppose you have two clocks which both keep perfect time: whenever one points to the hour, the other will strike, so that if you saw one and heard the other, you would think the one caused the other to strike. So it is with mind and body. Each is wound up by God to keep time with the other, so that, on occasion of my volition, purely physical laws cause my arm to move, although my will has not really acted on my body.
There were of course difficulties in this theory. In the first place, it was very odd; in the second place, since the physical series was rigidly determined by natural laws, the mental series, which ran parallel to it, must be equally deterministic. If the theory was valid, there should be a sort of possible dictionary, in which each cerebral occurrence would be translated into the corresponding mental occurrence. An ideal calculator could calculate the cerebral occurrence by the laws of dynamics, and infer the concomitant mental occurrence by means of the “dictionary.” Even without the “dictionary,” the calculator could infer any words and actions, since these are bodily movements. This view would be difficult to reconcile with Christian ethics and the punishment of sin.
These consequences, however, were not at once apparent. The theory appeared to have two merits. The first was that it made the soul, in a sense, wholly independent of the body, since it was never acted on by the body. The second was that it allowed the general principle: “one substance cannot act on another.” There were two substances, mind and matter, and they were so dissimilar that an interaction seemed inconceivable. Geulincx’s theory explained the appearance of interaction while denying its reality.
In mechanics, Descartes accepts the first law of motion, according to which a body left to itself will move with constant velocity in a straight line. But there is no action at a distance, as later in Newton’s theory of gravitation. There is no such thing as a vacuum, and there are no atoms; yet all interaction is of the nature of impact. If we knew enough, we should be able to reduce chemistry and biology to mechanics; the process by which a seed develops into an animal or a plant is purely mechanical. There is no need of Aristotle’s three souls; only one of them, the rational soul, exists, and that only in man.
With due caution to avoid theological censure, Descartes develops a cosmogony not unlike those of some pre-Platonic philosophers. We know, he says, that the world was created as in Genesis, but it is interesting to see how it might have grown naturally. He works out a theory of the formation of vortices: round the sun there is an immense vortex in the plenum, which carries the planets round with it. The theory is ingenious, but cannot explain why planetary orbits are elliptical, not circular. It was generally accepted in France, where it was only gradually ousted by the Newtonian theory. Cotes, the editor of the first English edition of Newton’s Principia, argues eloquently that the vortex theory leads to atheism, while Newton’s requires God to set the planets in motion in a direction not towards the sun. On this ground, he thinks, Newton is to be preferred.
I come now to Descartes’s two most important books, so far as pure philosophy is concerned. These are the Discourse on Method (1637) and the Meditations ( 1642). They largely overlap, and it is not necessary to keep them apart.
In these books Descartes begins by explaining the method of “Cartesian doubt,” as it has come to be called. In order to have a firm basis for his philosophy, he resolves to make himself doubt everything that he can manage to doubt. As he foresees that the process may take some time, he resolves, in the meanwhile, to regulate his conduct by commonly received rules; this will leave his mind unhampered by the possible consequences of his doubts in relation to practice.
He begins with scepticism in regard to the senses. Can I doubt, he says, that I am sitting here by the fire in a dressing-gown? Yes, for sometimes I have dreamt that I was here when in fact I was naked in bed. (Pyjamas, and even nightshirts, had not yet been invented.) Moreover madmen sometimes have hallucinations, so it is possible that I may be in like case.
Dreams, however, like painters, present us with copies of real things, at least as regards their elements. (You may dream of a winged horse, but only because you have seen horses and wings.) Therefore corporeal nature in general, involving such matters as extension, magnitude, and number, is less easy to question than beliefs about particular things. Arithmetic and geometry, which are not concerned with particular things, are therefore more certain than physics and astronomy; they are true even of dream objects, which do not differ from real ones as regards number and extension. Even in regard to arithmetic and geometry, however, doubt is possible. It may be that God causes me to make mistakes whenever I try to count the sides of a square or add 2 to 3. Perhaps it is wrong, even in imagination, to attribute such unkindness to God, but there might be an evil demon, no less cunning and deceitful than powerful, employing all his industry in misleading me. If there be such a demon, it may be that all the things I see are only illusions of which he makes use as traps for my credulity.
There remains, however, something that I cannot doubt: no demon, however cunning, could deceive me if I did not exist. I may have no body: this might be an illusion. But thought is different. “While I wanted to think everything false, it must necessarily be that I who thought was something; and remarking that this truth, I think, therefore I am, was so solid and so certain that all the most extravagant suppositions of the sceptics were incapable of upsetting it, I judged that I could receive it without scruple as the first principle of the philosophy that I sought.”*
This passage is the kernel of Descartes’s theory of knowledge, and contains what is most important in his philosophy. Most philosophers since Descartes have attached importance to the theory of knowledge, and their doing so is largely due to him. “I think, therefore I am” makes mind more certain than matter, and my mind (for me) more certain than the minds of others. There is thus, in all philosophy derived from Descartes, a tendency to subjectivism, and to regarding matter as something only knowable, if at all, by inference from what is known of mind. These two tendencies exist both in Continental idealism and in British empiricism—in the former triumphantly, in the latter regretfully. There has been, in quite recent times, an attempt to escape from this subjectivism by the philosophy known as instrumentalism, but of this I will not speak at present. With this exception, modern philosophy has very largely accepted the formulation of its problems from Descartes, while not accepting his solutions.
The reader will remember that Saint Augustine advanced an argument closely similar to the cogito. He did not, however, give prominence to it, and the problem which it is intended to solve occupied only a small part of his thoughts. Descartes’s originality, therefore, should be admitted, though it consists less in inventing the argument than in perceiving its importance.
Having now secured a firm foundation, Descartes sets to work to rebuild the edifice of knowledge. The I that has been proved to exist has been inferred from the fact that I think, therefore I exist while I think, and only then. If I ceased to think, there would be no evidence of my existence. I am a thing that thinks, a substance of which the whole nature or essence consists in thinking, and which needs no place or material thing for its exist
ence. The soul, therefore, is wholly distinct from the body and easier to know than the body; it would be what it is even if there were no body.
Descartes next asks himself: why is the cogito so evident? He concludes that it is only because it is clear and distinct. He therefore adopts as as a general rule the principle: All things that we conceive very clearly and very distinctly are true. He admits, however, that there is sometimes difficulty in knowing which these things are.
“Thinking” is used by Descartes in a very wide sense. A thing that thinks, he says, is one that doubts, understands, conceives, affirms, denies, wills, imagines, and feels—for feeling, as it occurs in dreams, is a form of thinking. Since thought is the essence of mind, the mind must always think, even during deep sleep.
Descartes now resumes the question of our knowledge of bodies. He takes as an example a piece of wax from the honeycomb. Certain things are apparent to the senses: it tastes of honey, it smells of flowers, it has a certain sensible colour, size and shape, it is hard and cold, and if struck it emits a sound. But if you put it near the fire, these qualities change, although the wax persists; therefore what appeared to the senses was not the wax itself. The wax itself is constituted by extension, flexibility, and motion, which are understood by the mind, not by the imagination. The thing that is the wax cannot itself be sensible, since it is equally involved in all the appearances of the wax to the various senses. The perception of the wax “is not a vision or touch or imagination, but an inspection of the mind.” I do not see the wax, any more than I see men in the street when I see hats and coats. “I understand by the sole power of judgement, which resides in my mind, what I thought I saw with my eyes.” Knowledge by the senses is confused, and shared with animals; but now I have stripped the wax of its clothes, and mentally perceive it naked. From my sensibly seeing the wax, my own existence follows with certainty, but not that of the wax. Knowledge of external things must be by the mind, not by the senses.
This leads to a consideration of different kinds of ideas. The commonest of errors, Descartes says, is to think that my ideas are like outside things. (The word “idea” includes sense-perceptions, as used by Descartes.) Ideas seem to be of three sorts: (1) those that are innate, (2) those that are foreign and come from without, (3) those that are invented by me. The second kind of ideas, we naturally suppose, are like outside objects. We suppose this, partly because nature teaches us to think so, partly because such ideas come independently of the will (i.e., through sensation), and it therefore seems reasonable to suppose that a foreign thing imprints its likeness on me. But are these good reasons? When I speak of being “taught by nature” in this connection, I only mean that I have a certain inclination to believe it, not that I see it by a natural light. What is seen by a natural light cannot be denied, but a mere inclination may be towards what is false. And as for ideas of sense being involuntary, that is no argument, for dreams are involuntary although they come from within. The reasons for supposing that ideas of sense come from without are therefore inconclusive.
Moreover there are sometimes two different ideas of the same external object, e.g., the sun as it appears to the senses and the sun in which the astronomers believe. These cannot both be like the sun, and reason shows that the one which comes directly from experience must be the less like it of the two.
But these considerations have not disposed of the sceptical arguments which threw doubt on the existence of the external world. This can only be done by first proving the existence of God.
Descartes’s proofs of the existence of God are not very original; in the main they come from scholastic philosophy. They were better stated by Leibniz, and I will omit consideration of them until we come to him.
When God’s existence has been proved, the rest proceeds easily. Since God is good, He will not act like the deceitful demon whom Descartes has imagined as a ground for doubt. Now God has given me such a strong inclination to believe in bodies that He would be deceitful if there were none; therefore bodies exist. He must, moreover, have given me the faculty of correcting errors. I use this faculty when I employ the principle that what is clear and distinct is true. This enables me to know mathematics, and physics also, if I remember that I must know the truth about bodies by the mind alone, not by mind and body jointly.
The constructive part of Descartes’s theory of knowledge is much less interesting than the earlier destructive part. It uses all sorts of scholastic maxims, such as that an effect can never have more perfection than its cause, which have somehow escaped the initial critical scrutiny. No reason is given for accepting these maxims, although they are certainly less self-evident than one’s own existence, which is proved with a flourish of trumpets. Plato’s Theaetetus, Saint Augustine, and Saint Thomas contain most of what is affirmative in the Meditations.
The method of critical doubt, though Descartes himself applied it only half-heartedly, was of great philosophic importance. It is clear, as a matter of logic, that it can only yield positive results if scepticism is to stop somewhere. If there is to be both logical and empirical knowledge, there must be two kinds of stopping points: indubitable facts, and indubitable principles of inference. Descartes’s indubitable facts are his own thoughts—using “thought” in the widest possible sense. “I think” is his ultimate premiss. Here the word “I” is really illegitimate; he ought to state his ultimate premiss in the form “there are thoughts.” The word “I” is grammatically convenient, but does not describe a datum. When he goes on to say “I am a thing which thinks,” he is already using uncritically the apparatus of categories handed down by scholasticism. He nowhere proves that thoughts need a thinker, nor is there reason to believe this except in a grammatical sense. The decision, however, to regard thoughts rather than external objects as the prime empirical certainties was very important, and had a profound effect on all subsequent philosophy.
In two other respects the philosophy of Descartes was important. First: it brought to completion, or very nearly to completion, the dualism of mind and matter which began with Plato and was developed, largely for religious reasons, by Christian philosophy. Ignoring the curious transactions in the pineal gland, which were dropped by the followers of Descartes, the Cartesian system presents two parallel but independent worlds, that of mind and that of matter, each of which can be studied without reference to the other. That the mind does not move the body was a new idea, due explicitly to Geulincx but implicitly to Descartes. It had the advantage of making it possible to say that the body does not move the mind. There is a considerable discussion in the Meditations as to why the mind feels “sorrow” when the body is thirsty. The correct Cartesian answer was that the body and the mind were like two clocks, and that when one indicated “thirst” the other indicated “sorrow.” From the religious point of view, however, there was a grave drawback to this theory; and this brings me to the second Characteristic of Cartesianism that I alluded to above.
In the whole theory of the material world, Cartesianism was rigidly deterministic. Living organisms, just as much as dead matter, were governed by the laws of physics; there was no longer need, as in the Aristotelian philosophy, of an entelechy or soul to explain the growth of organisms and the movements of animals. Descartes himself allowed one small exception: a human soul could, by volition, alter the direction though not the quantity of the motion of the animal spirits. This, however, was contrary to the spirit of the system, and turned out to be contrary to the laws of mechanics; it was therefore dropped. The consequence was that all the movements of matter were determined by physical laws, and, owing to parallelism, mental events must be equally determinate. Consequently Cartesians had difficulty about free will. And for those who paid more attention to Descartes’s science than to his theory of knowledge, it was not difficult to extend the theory that animals are automata: why not say the same of man, and simplify the system by making it a consistent materialism? This step was actually taken in the eighteenth century.
There is in
Descartes an unresolved dualism between what he learnt from contemporary science and the scholasticism that he had been taught at La Flèche. This led him into inconsistencies, but it also made him more rich in fruitful ideas than any completely logical philosopher could have been. Consistency might have made him merely the founder of a new scholasticism, whereas inconsistency made him the source of two important but divergent schools of philosophy.
* Descartes says it was a stove (poêle), but most commentators think this impossible. Those who know old-fashioned Bavarian houses, however, assure me that it is entirely credible.
* The above argument, “I think, therefore I am” (cogito ergo sum), is known as Descartes’s cogito, and the process by which it is reached is called “Cartesian doubt.”
CHAPTER X
Spinoza
SPINOZA (1634-77) is the noblest and most lovable of the great philosophers. Intellectually, some others have surpassed him, but ethically he is supreme. As a natural consequence, he was considered, during his lifetime and for a century after his death, a man of appalling wickedness. He was born a Jew, but the Jews excommunicated him. Christians abhorred him equally ; although his whole philosophy is dominated by the idea of God, the orthodox accused him of atheism. Leibniz, who owed much to him, concealed his debt, and carefully abstained from saying a word in his praise; he even went so far as to lie about the extent of his personal acquaintance with the heretic Jew.
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