Routledge History of Philosophy Volume IV

356 LEIBNIZ: TRUTH, KNOWLEDGE AND METAPHYSICS
ascribe modes and states to the composing entities without any need to
refer to the aggregate itself. 8
Thus, a proposition such as ‘The army fought bravely’ is reducible to
propositions which ascribe various properties to the members of the aggregate,
namely, the individual soldiers.
Perhaps more controversial is the second premise of the argument. A nonorganic
body such as a block of marble does not seem to be on a par with clearcut
examples of aggregates such as an army or a flock of sheep. Leibniz must
admit that a block of marble is more tightly bonded than these aggregates, but he
would claim that this fact is not metaphysically significant; a block of marble is
no less an entity by aggregation than a flock of sheep. 9 But in that case what is a
block of marble an aggregate of? At first sight it seems that Leibniz would say that
a block of marble is an aggregate of physical parts which are themselves aggregates
and so on ad infinitum. But though he shows some hesitancy on this issue, in the
correspondence with Arnauld Leibniz suggests that a marble slab is an aggregate
of organisms no less than a flock of sheep: ‘perhaps this marble block is merely a
heap of an infinite number of living bodies, or is like a lake full of fish, although
these animals are ordinarily visible only in half-rotten bodies.’ 10 This thesis draws
support from the empirical discoveries made possible by the recent invention of
the microscope.
Thus Leibniz reaches an important negative conclusion which is in obvious
conflict with Cartesian theses; no non-organic bodies are substances. 11 But this
conclusion still leaves open the question of Leibniz’s positive views on the issue
of what items qualify as substances. Recent work has shown that around the time
of the Discourse on Metaphysics Leibniz was remarkably hesitant on this issue;
indeed, he flirted with a number of possible positions. 12 He was perhaps
particularly uncertain as to whether anything physical counted as a substance,
but as we shall see, he also had doubts about the ontological status of souls.
Despite his hesitations, the view to which he seems to have been most attracted
is that organisms, and perhaps souls, are the only substances; organisms are what
Leibniz calls ‘corporeal substances’. With regard to physical objects, then,
Leibniz’s teaching is that every body is either itself a corporeal substance or an
aggregate of corporeal substances.
Leibniz’s somewhat tentative positive thesis raises an obvious question: why are
organisms better candidates for substantiality than non-organic bodies? Leibniz’s
short answer to this question is clear: organisms are not just aggregates but true
unities, and every entity which is endowed with a true unity is a substance. For
Leibniz, an organism is truly one by virtue of possessing a soul or principle of
life which confers unity on it; in scholastic terminology the soul is said to inform
the body. Indeed, Leibniz even goes so far as to revive the scholastic doctrine
that the soul is the substantial form of the body; here he is drawing on the fact
that in medieval philosophy it is the presence of a substantial form that makes a
body a natural unity. 13