Routledge History of Philosophy Volume IV

358 LEIBNIZ: TRUTH, KNOWLEDGE AND METAPHYSICS
the chopping up of a table; in both cases we are simply left with parts of the
original body. In reply Leibniz seeks to reconcile the facts about the case of the
worm with his thesis that animals are genuine substances which possess true
unity by virtue of the souls which animate them. From the fact that both parts of
the worm continue to move, it does not follow that we must postulate either two
souls or none. The soul may continue to animate one of the parts, and it is this part
which is strictly to be identified with the worm. In this sense the worm survives
the division of its body. 18 LOGIC AND METAPHYSICS
The originally Aristotelian idea of substance as an ultimate subject of predication
thus plays a major role in the Discourse on Metaphysics and the correspondence
with Arnauld; it provides the basis for Leibniz’s persistent claim that substances
are genuine unities. But as we have seen, Leibniz thinks that the Aristotelian
doctrine does not go far enough. In the Discourse on Metaphysics Leibniz seeks
a deeper understanding of what is involved in being a substance, and he finds it
in what we may call the ‘complete concept theory’: this is the famous claim that
‘the nature of an individual substance or a complete being is to have a notion so
complete that it is sufficient to contain and to allow us to deduce from it all the
predicates of the subject to which the notion is attributed’. 19 In the following
sections of the Discourse Leibniz develops a train of thought which led Bertrand
Russell and the French scholar, Couturat, to claim that Leibniz derived his
metaphysics from his logic. 20
As a general theory about the roots of Leibniz’s metaphysics, the Russell-
Couturat thesis has come in for a good deal of criticism. For one thing, the thesis
does not seem to apply to the writings of Leibniz’s later period; there purely
logical theories seem to play little or no role in generating metaphysical
doctrines. Even at the time of the Discourse, Leibniz appeals to non-logical
considerations in support of his metaphysics. Leibniz invokes his physical theory
that in collisions ‘bodies really recede from other bodies through the force of
their own elasticity, and not through any alien force’. 21 In this way Leibniz seeks
to confirm his metaphysical doctrine that there is no causal interaction between
substances. Moreover, at least as formulated by Russell, the so-called ‘logicist’
thesis suffers from a different kind of difficulty. According to Russell, Leibniz
validly derived his metaphysics from his logic; against this, it has been remarked
that there are in fact serious problems with the purported deduction.
Considerations like these have led some writers to argue that Leibniz did not so
much derive his metaphysics from his logic as tailor his logic to a metaphysics to
which he is attracted for independent reasons. 22 Nonetheless, there does seem to
be some truth in the Russell-Couturat thesis. At least in the Discourse and other
writings of the same period, Leibniz certainly seems to rely on logical premises
in arguing for metaphysical conclusions. This is not to say that as it stands the