Routledge History of Philosophy Volume IV

354 LEIBNIZ: TRUTH, KNOWLEDGE AND METAPHYSICS
how in his later writings Leibniz abandons his theory of corporeal substance for
a form of idealism; this is the famous doctrine of monads. In the fourth section we
shall look at the anti-Newtonian theories of space and time which Leibniz
formulated at the very end of his career. In the following section we shall study
Leibniz’s somewhat ill-conceived attempt to apply his general theory of causality
to the problem of the relationship between mind and body which Descartes
bequeathed to his successors. Finally, in the last two sections we shall analyse
Leibniz’s psychology and his theory of knowledge; here we shall see how
Leibniz seeks to reinterpret some ideas deriving from Descartes and Spinoza.
THE ARISTOTELIAN BACKGROUND: SUBSTANCE
AND AGGREGATE
The synthesizing spirit of Leibniz’s philosophy is clearly visible in Leibniz’s
first mature work, the Discourse on Metaphysics, and in the correspondence with
Arnauld which it precipitated. One way of looking at these works is to see that
Leibniz is trying to revive Aristotelian doctrines about substance and to show that
they are in conformity with the new science; indeed, they are largely free of the
conceptual difficulties which plague the more recent Cartesian ideas. It is true
that Leibniz thinks that Aristotle did not say the last word about substance. But it
is still possible to see Leibniz as engaged in extending, rather than replacing, the
Aristotelian project.
We must begin by reminding ourselves of two very influential claims that
Aristotle made about substance. First, for Aristotle, a substance is what may be
termed an ‘ultimate subject of predication’. Thus, by this criterion Alexander is a
substance because while we can predicate properties of Alexander—we can say,
for instance, that he was a Macedonian—he himself is not predicable of anything
else; there is nothing of which we can say that it is an Alexander. To put the point
another way, the noun ‘Alexander’ can appear only in the subject position in a
sentence and never in the predicate position. By contrast, honesty is a subject of
predication but not an ultimate one; for though we can predicate properties of
honesty, honesty itself is predicable of other things—for instance, a person who
possesses the virtue. 3 Second, in response to the characteristically Greek
preoccupation with flux, Aristotle claims that substances are substrata of change:
‘The most distinctive mark of substance appears to be that while remaining
numerically one and the same, it is capable of admitting contradictory qualities.’ 4
Thus, although he never instantiates both properties simultaneously, Alexander
as an infant is two feet tall and as an adult, say, six feet tall. To say that
Alexander is a substance is a way of drawing our attention to the fact that one
and the same individual persists through the change in qualities. The relation
between these two claims about substance is not entirely clear, but on the face of
it, they do not seem to be equivalent; it seems that there could be items which are
ultimate subjects of predication, even though they do not persist through time. A