Routledge History of Philosophy Volume IV

366 LEIBNIZ: TRUTH, KNOWLEDGE AND METAPHYSICS
Leibniz held that, though in the abstract, matter is infinitely divisible, taken
concretely it is composed of organisms which are material beings endowed with
souls, and that these organisms are genuinely basic entities. In his later
philosophy Leibniz may have continued to hold that matter is in some sense
composed of organisms, but he gave up the thesis that organisms are genuinely
basic entities or intrinsic natural unities.
Why, then, did Leibniz give up the view that organisms are basic entities? A
plausible answer is that he came to feel that some of the claims about substance
which he had deduced from his logic did not clearly apply to organisms.
According to the Discourse substances are indivisible but, as we saw earlier, in
the correspondence with Arnauld Leibniz had difficulty defending the thesis that
organisms are indivisible. Possibly Leibniz became dissatisfied with his answer
to Arnauld’s puzzle about the worm that is cut in two. By contrast, monadology
is largely free from these difficulties: as a simple, immaterial being a monad
satisfies the indivisibility criterion much more clearly than an organism.
Moreover, the earlier, Aristotelian metaphysics fares less well than monadology
in accommodating the thesis that there is no causal interaction between
substances. In the earlier metaphysics this thesis implies that no two organisms
interact, but it has no such implications for other bodies; for instance, it does not
entail that no two billiard balls interact. And this may well have come to seem
arbitrary to Leibniz. By contrast, monadology suffers from no such problem. For
one thing, it is perhaps fairly intuitive to say that souls cannot causally interact.
But in any case, by restricting the thesis to souls or soul-like entities, Leibniz is at
least able to escape the charge that he is simply drawing an arbitrary line through
the physical world.
An obvious problem for an idealist philosopher who holds that reality is
ultimately spiritual is to determine the status of bodies. Leibniz’s idealism
certainly implies that bodies cannot be substances, but beyond that it leaves their
status unspecified. For one thing, idealism does not discriminate between
eliminativist and reductionist approaches to this issue; in other words, it does not
discriminate between the thesis that bodies do not exist and the thesis that,
although bodies exist, they are to be reduced to something which is ontologically
more basic. Fortunately, on this issue Leibniz leaves us in no doubt about his
position: in a letter to De Volder he remarks:
I do not really eliminate body, but I reduce it to what it is. For I show that
corporeal mass, which is thought to have something over and above simple
substance, is not a substance, but a phenomenon resulting from simple
substances, which alone have unity and absolute reality. 47
Leibniz is thus in some sense a reductionist about bodies; what is less clear is the
nature of the reduction. Some writers have claimed that Leibniz anticipated
Berkeley’s phenomenalism; they have thought that he came to espouse the thesis