Routledge History of Philosophy Volume IV

SPINOZA: METAPHYSICS AND KNOWLEDGE 265
and thinking substance, he implied that each has many attributes (Principles of
Philosophy, Pt I, 53; CSM i, 210), understanding by an attribute (ibid., Pt I, 56)
that which always remains unmodified, such as existence and duration in the
case of created things. Each substance, however, has one ‘principal attribute’,
and these are extension in the case of corporeal substance and thought in the case
of thinking substance. Spinoza and Descartes, then, agree in holding that one
must explain physical nature in terms of extension and mental states and events
in terms of thought. They also agree to some extent (though here there are also
important differences) that we must explain the former in terms of extension
alone and the latter in terms of thought alone. Descartes expresses this by saying
(Meditation VI, CSM ii, 54) that corporeal and thinking substance are ‘really
distinct’. 53 Spinoza would say that Descartes was right in holding that we cannot
mix mental terms with physical terms when we try to explain either mind or
matter—still less can we reduce mental terms to physical terms (as in the case of
materialism) or physical terms to mental terms. But, he would say, the
metaphysics in terms of which Descartes made this point was seriously at fault.
Contrary to Descartes, there is only one substance, and what Descartes says in
terms of two substances must be translated into terms of the attributes of thought
and extension, each of which is ‘conceived through itself’. 54
Spinoza would also argue that by regarding thought and extension in this way
—as self-enclosed attributes, which are attributes of one substance—he can solve
a problem which had faced Descartes: that of the relation between mind and
body. Descartes wanted to maintain two theses: first, that corporeal and mental
substance are really distinct, but second, that mind and body act on each other,
and indeed that the human being is a unity of mind and body. The problem for
Descartes was to explain how these propositions can both be true, and Spinoza
thought (as many others have thought) that he failed to do so. To grasp Spinoza’s
solution, however, it is necessary to go further into his system. This is because the
problem is one which concerns particular minds and particular bodies, and this
means that one has to see how Spinoza accommodates these within his system.
That is, it is necessary to consider his theory of ‘modes’.
Spinoza argues, not only that the infinite substance must be unique, but that it
must also be indivisible, and that the same can be said of any of its attributes. 55
This raises the question of how the indivisible substance, or its indivisible
attributes, is to be related to the particular things that we meet in our experience.
That is, it raises the question: what is the place of the concept of a particular
thing in Spinoza’s system? The answer is that it enters by way of the concept of a
‘mode’. Particular things, Spinoza says, are simply ‘modes by which attributes of
God are expressed in a certain and determinate manner’. 56 Spinoza has already
defined a mode in the fifth of the definitions of Part I of the Ethics, saying that it
is ‘that which is in something else, through which it is also conceived’. This
definition can be illuminated by relating it to what Descartes has to say about
real and modal distinctions. For Descartes, a real distinction holds between two
or more substances, and is recognized by the fact that one can be clearly and