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
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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 deceit-
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ful 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
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* 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 cared “Cartesian doubt.”
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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 existence. 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 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 out-
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side 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
