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-