History of Western Philosophy - Bertrand Russell [319]
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.'2
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