Routledge History of Philosophy Volume IV

SPINOZA: METAPHYSICS AND KNOWLEDGE 269
anticipate, Spinoza holds that a true idea fits, and a false idea does not fit, into an
explanatory system, and it may be that the relation between an idea and its
attribute has to be conceived along such lines. However, perhaps enough has
been said here about Spinoza’s theory of ideas to enable one to grasp his answer
to the problem posed on p. 287—the problem of mind-matter relations.
It will be recalled that the problem arose for Descartes because he wanted to
maintain two propositions. On the one hand, he wanted to say that mind and
body are ‘really distinct’; on the other hand, he felt compelled to grant that,
despite this, mind and body act on one another, and indeed that the human being
is a unity of mind and matter. Spinoza’s answer to the problem is given in terms
of his theory of attributes and modes. In effect, he holds that Descartes was right
in saying (Reply to First Objections, CSM ii, 86) that one has a complete
understanding of what a body is without ascribing to it anything that belongs to
the nature of a mind, and conversely in the case of a mind. Descartes’s error,
Spinoza would say, lay in his supposition that there must exist substances of
basically different kinds, namely mental and corporeal substances. Really, there
exists just one substance with different attributes, each of which (and here
Spinoza expresses a qualified agreement with Descartes) must be ‘conceived
through itself’.
It is because the attributes are conceived through themselves that we must
explain physical states and events in physical terms only, and mental states and
events in mental terms only. Yet the human mind and body are not wholly
unrelated; for any state of or event in the one there is a corresponding state of or
event in the other. This is because thought and extension are different attributes
of one and the same substance. As Spinoza puts it in an important note to
Proposition 7 of Part II of the Ethics,
A mode of extension and the idea of that mode are one and the same thing,
but expressed in two ways…. For example, a circle existing in nature and
the idea of an existing circle…is one and the same thing, though explained
through different attributes.
In Proposition 2 of Part III of the Ethics, Spinoza observes that it follows from
what he has said about the nature of the attributes that ‘The body cannot
determine the mind to think, nor the mind the body to motion, nor to rest.’ As he
recognizes, this may seem paradoxical. Suppose, for example, 66 that some
craftsman is building a temple; surely the craftsman’s mind must guide the
movements of his hands? Spinoza replies that this cannot be so, and that people
only suppose that it must be so because ‘they know not what a body can do, or
what can be deduced from mere contemplation of its nature’. He goes on to hint
that, when people think of the capabilities of the human body, they tend to think
in terms of the machines they can construct. But ‘the construction of the human
body (corporis humani fabrica 67 )…far surpasses any piece of work made by