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