Routledge History of Philosophy Volume IV

120 SCIENCE AND MATHEMATICS UP TO DESCARTES
The extent of Galileo’s reliance upon mathematics, sometimes to the neglect
of exact correspondence with empirical facts, may have worried a good
Baconian, but to his younger contemporary René Descartes the principal fault lay
in a different direction. Writing to Marin Mersenne in 1638, shortly after the
publication of the Discorsi, he gave the opinion that, although Galileo
‘philosophized much better than most, yet he has only sought the reasons of
certain particular effects without considering the first causes of nature, and so
has built without foundation’. 43 This was to be seen as contrasting with
Descartes himself, whose science of mechanics depended intimately upon both
his method and metaphysics, and whose Discours de la Méthode, together with
the Diotrique, Météores and Géométrie, had been published in the preceding
year. And before that Descartes had almost completed his Le Monde, a major
work on natural philosophy, which, as noted above, he then suppressed because
of Galileo’s condemnation in 1633.
After Descartes had in a familiar manner proved to his own satisfaction the
existence of himself, of God, and of an external physical world, he was in a
position to consider more exactly the nature of the last of these. And a very
austere picture it was that he had of it. As he put it in the Principia Philosophiae
(published in 1644), if we attend to the intellect, rather than the senses,
We shall easily admit that it is the same extension that constitutes the
nature of body and the nature of space, nor do these two differ from each
other more than the nature of the genus or species differs from the nature
of the individual. If while attending to the idea which we have of a body,
for example a stone, we reject from it all that we recognize as not required
for the nature of body, let us certainly first reject hardness, for if a stone is
liquefied or divided into the minutest particles of dust, it will lose this, but
will not on that account cease to be body; let us also reject colour, for we
often see stones so transparent as there were no colour in them; let us
reject heaviness, for although fire is so light, we do not the less think it to
be body; and then finally let us reject cold and heat, and all other qualities,
because either they are not considered to be in the stone, or, if they are
changed, the stone is not on that account thought to have lost the nature of
body. We shall then be aware that nothing plainly remains in the idea of it
other than that it is something extended in length, breadth and depth, and
the same is contained in the idea of space, not only full of bodies, but also
that which is called a vacuum. 44
In this way the physical universe is reduced to characterless matter swirling
around in the famous Cartesian vortices, and by its actions on our sense organs
producing our perceptions of all the different qualities.
Descartes’s physical universe has certain similarities with that of the ancient
atomists, but there were important differences. In the first place, matter for
Descartes was not composed of indivisible atoms moving in void, but constituted