Routledge History of Philosophy Volume IV

DESCARTES: METAPHYSICS AND THE PHILOSOPHY OF MIND 203
By the time this full-blown argument is deployed in the Sixth Meditation,
Descartes has more resources at his disposal than he had in the Discourse when
he blandly observed that he could pretend he did not have a body without thereby
pretending that the ‘I by which I am what I am’ did not exist. In the Sixth
Meditation, God (whose existence is taken to have been proved at this stage) is
invoked as the guarantor of the clear and distinct perceptions of the human mind.
Hence, if we can clearly and distinctly conceive of X without Y, it follows that Y
cannot be essential to X. The modern reader may feel uncomfortable here: surely
all the argument proves is that mind and body could conceivably exist
separately, not that they are in fact separate entities. But it is precisely the
conceivability of mind separate from body which Descartes relies on in order to
establish his dualistic thesis: ‘the mere fact that I can clearly and distinctly
understand one thing apart from another is enough to make me certain that the
two things are distinct, since they are capable of being separated, at least by
God.’ 86 Whether in fact the mind will exist after the death of the body is
something that Descartes is content to leave undetermined by reason: it is a
matter of religious faith. 87 It is enough that it is, as we should say nowadays,
logically possible that it should exist without physical matter. That possibility,
which Descartes takes himself to have demonstrated, is enough to guarantee the
incorporeality thesis—that what makes me me, the conscious awareness of
myself as a res cogitans, cannot depend on the existence of any physical object.
What the above analysis suggests is that Descartes’s version of dualism stands
or falls with the claim that the existence of mind without matter is at least a
logical possibility. And a good many modern philosophers, however adamantly
they may be disposed to insist that mental properties are structural or functional
properties of a physical or biological system (the brain, the nervous system),
often concede that disembodied consciousness is at least logically conceivable.
But what does the alleged logical possibility of mind without matter amount to?
It must presumably boil down to some such claim as that there is no logical
contradiction in conjoining (as Descartes does in the Discourse) the two
statements (a) ‘I exist as a conscious being at time t’ and (b) ‘my body (including
my brain and nervous system) does not exist at time t’. But this seems a very
weak argument. As Leibniz was later to observe (in a rather different context), it
is not enough, to establish the coherence of a set of propositions, that one cannot
immediately detect any obvious inconsistency in them. For it is quite possible
that a set of propositions which seems consistent on the face of it might turn out
on further analysis to contain hitherto undetected incoherence. 88 Borrowing the
terminology of Karl Popper from our own time (and transferring it from the
realm of philosophy of science to that of logic), we may say that claims of
logical possibility are falsifiable (by producing a contradiction) but not
conclusively verifiable. Now admittedly, when we are dealing with very simple
and transparent truths (those of elementary arithmetic or geometry, for example),
we may be entitled to be sure that there could be no hidden inconsistency which
would undermine the logical coherence of a group of propositions. But when we