Routledge History of Philosophy Volume IV

DESCARTES: METAPHYSICS AND THE PHILOSOPHY OF MIND 207
the gland that special movement which represents the same object to the
soul, and makes it recognize the object as the one it wanted to remember. 99
What strikes the reader here is not so much the wealth of obsolete physiological
detail (modern readers will readily be able to substitute electrochemical events in
the cerebral cortex for Descartes’s movements of the pineal gland and ‘animal
spirits’) as the way in which that physiological detail is expected to ‘mesh’ with
events in the non-physical realm of the soul. Descartes has managed to supply a
host of mechanisms whereby movements, once initiated in the pineal gland, can
be transferred to other parts of the brain and body; but he does not seem to have
tackled the central issue of how an incorporeal soul can initiate such movements
in the first place. And the same problem will apply when the causal flow is in the
other direction. Descartes devotes a lot of attention to the physiological
mechanisms whereby bodily stimuli of various kinds cause changes in the
nervous system and brain which ‘dispose’ the soul to feel emotions like anger or
fear. 100 But he does not explain how mere brain events, however complex their
physiological genesis, could have the power to arouse or excite events in the
mental realm.
Why exactly is the causal aspect of the mind-body relation problematic for
Descartes? The answer, in brief, is that throughout the rest of his metaphysics
and physics he seems to presuppose that causal transactions should be in some
sense transparent to the human intellect. ‘The effect is like the cause’ was a
standard maxim of the scholastics which (as noted earlier in this chapter)
Descartes readily accepts. 101 In his causal proofs of God’s existence he relies on
the principle that the cause of an object possessing a given degree of perfection
must itself possess as much or more perfection: whatever is found in the effect must
be present in the cause. In physics, too, Descartes often seems inclined to require
explanations that reveal transparent connections between causes and effects (in
the unfolding of the laws of motion, for example, a simple transmission model is
invoked—a cause transmits or passes on a determinate quantity of motion to its
effect). 102 In all these cases, Descartes apparently wants to be able to appeal to
something very simple and self-evident: if we could not ‘see’ how effects
inherited features from their causes, we would have a case of something arising
‘from nothing’, which would be absurd. But now it is immediately clear that no
such transparency could be available in the mindbody interactions which
Descartes describes in such detail in the Passions of the Soul. Transparent
connections can be unfolded so long as we remain within the realm of
physiology and trace how the stimulation of a sense organ generates changes in
the ‘animal spirits’ which in turn cause modifications in the movements of the
pineal gland. But at the end of the story, there will be a mental event which
simply ‘arises’ in the soul: the smooth progression of causal explanations
abruptly jolts to a halt. Whatever it is that bridges the gulf between the bodily
and the mental realms, it seems that it must remain opaque to causal explanation,
in the sense in which that notion is normally understood by Descartes. 103