Routledge History of Philosophy Volume IV

364 LEIBNIZ: TRUTH, KNOWLEDGE AND METAPHYSICS
sharp this transition was, and it is true that there are times in his later writings
when Leibniz speaks as if there really are corporeal substances. But the
dominant character of Leibniz’s later metaphysics is well represented by his
remark to De Volder: ‘Considering the matter carefully, it must be said that there
is nothing in the world except simple substances and in them, perception and
appetite.’ 41 Taken strictly, this claim implies that there are no corporeal
substances.
The term ‘monad’ derives from a Greek word for unity. The fact that Leibniz
chose this term to denote the fundamental entities in his later metaphysics shows
that there is continuity in his thought; as before in the Discourse and the
correspondence with Arnauld, a substance is a genuine unity. But a monad, unlike
a corporeal substance, is a unity in a quite straightforward sense; it has no parts,
or, in other words, it is simple. Now the simplicity of monads is a clue to further
aspects of their nature. Since they are simple, monads are immaterial —which,
for Leibniz, means that they are spiritual, for everything material has parts. The
simplicity of monads also entails, for Leibniz, that they are indestructible. Here
the underlying idea is that destruction consists in decomposition, and that where
there are no parts, there can be no decomposition. Hence, in the case of monads,
‘there is no dissolution to fear’. 42
The fact that monads are immaterial and spiritual imposes a radical restriction
on the properties of which they are capable; it rules out all such physical
properties as size, shape and even position. As the quotation from the letter to De
Volder bears out, the basic properties of monads are perception and appetite, or
appetition. The notion of perception, which Leibniz defines as ‘the expression of
the many in the one’, 43 is central not just to Leibniz’s metaphysics but also to his
psychology, and it will accordingly be discussed in the penultimate section of
this chapter. But something may be said here about appetition. Appetition is the
dynamic principle in the monad; it is that by virtue of which a monad changes its
state. Yet, as one writer has suggested, it is possible that, for Leibniz, appetitions
and perceptions are not two kinds of modifications but rather the same
modification viewed differently.
From one point of view every passing state is an expression of the many in
the one and as such it is a perception. From the other point of view every
passing state is a tendency to a succeeding state and as such it is an
appetition. 44
A possible parallel would be Spinoza’s doctrine that every finite mode of
substance can be viewed under the attributes of both thought and extension.
The doctrine of monads is not merely idealistic; it is also in a sense monistic.
But the term ‘monism’ is a little misleading and needs clarification. Monadology
is certainly not monistic in the sense in which Spinoza’s metaphysics is
monistic; Leibniz is not asserting, as Spinoza does, that there is only one
substance (Deus seu Natura). Rather, monadology is monistic in the sense that,