Routledge History of Philosophy Volume IV

270 RENAISSANCE AND SEVENTEENTH-CENTURY RATIONALISM
human art’. So (Spinoza implies) there is no reason to think that the movements
of the craftsman’s hands cannot be explained in purely physical terms.
Spinoza’s theory of the relations between mind and body is often, and with
some justice, said to be a form of ‘psycho-physical parallelism’. By this is meant
the view that body does not act on mind, nor mind on body, but that the states of
mind and body are such that for each bodily state there is a corresponding mental
state and conversely; and similarly for bodily and mental events. However, to
describe Spinoza’s theory of mind-body relations in this way does not identify it
completely. This is because to talk of psycho-physical parallelism is to talk, not
of one theory, but of a group of theories. One could say, for example, that
Leibniz’s theory of pre-established harmony, 68 as applied to the relations
between mind and body, is a form of psycho-physical parallelism; but Leibniz’s
theory of mind-body relations is very different from Spinoza’s. To categorize
Spinoza’s theory more precisely, we have to consider his answer to the question
why the parallelism should hold. The answer, as we have seen, is that each
attribute is not only ‘conceived through itself but is also an attribute of one and
the same substance. Seen in this way, Spinoza’s theory of the relations between
mind and body is a classical form of what is often called the ‘double-aspect
theory’. 69 This theory is clearly defined in Baldwin’s Dictionary of Philosophy
and Psychology (London, 1901) as the theory which states that ‘mental and
bodily facts are parallel manifestations of a single underlying reality’. The theory
professes to overcome the onesidedness of materialism and idealism by
regarding both series as only different aspects of the same reality, like the
convex and the concave views of a curve; or, according to another
favourite metaphor, the bodily and the mental facts are really the same
facts expressed in different language.
Spinoza never calls an attribute an ‘aspect’ of substance; however, he often
describes the relation between substance and attribute in terms of expression (cf.
pp. 285–6), and it has just been noted (p. 292) that he says expressly that a mode
of extension and the corresponding mode of thought are ‘one and the same thing,
but expressed in two ways’.
What Spinoza has to say about the relation between God and his modes is
intimately connected with what he has to say about God as a cause. It has already
been seen that God is self-caused, causa sui (p. 282); but Spinoza also says that
God is the efficient cause of all modes. His reason for saying this 70 is that an
infinity of modes follows from the necessity of the divine nature. Now, by virtue
of Spinoza’s thesis that the causal relation is a logical relation (p. 283), this is the
same as saying that God is the cause of an infinity of modes.
In calling God an ‘efficient cause’, Spinoza is using traditional terminology,
which goes back to Aristotle. Such a cause, according to Aristotle, is a source of
change or coming to rest (Physics II, 3, 194 b29–32). So, for example, a man
who gave advice is a cause in this sense, and a father is the efficient cause of his