Routledge History of Philosophy Volume IV

SPINOZA: METAPHYSICS AND KNOWLEDGE 275
rests on sense experience, so there is knowledge that rests on induction; indeed,
in the Tractatus de Intellectus Emendatione Spinoza says that such knowledge is
of great importance in everyday life (G ii, 11). One may infer that Spinoza
regards such knowledge as defective in that it does not give us any satisfactory
explanation of why the inductive generalization holds. It tells us (say) that oil
feeds a fire, but does not tell us why it does so.
It is clear from all this why Spinoza should regard sense experience and
induction as involving inadequate ideas; what is not so clear is why he regards
them as providing us with knowledge. Some indication of an answer is provided
by the note to Proposition 17 of Part II of the Ethics, already quoted on pp. 291–
2. In this, Spinoza defends his postulates on the grounds that they contain
scarcely anything that is not borne out by experience. This itself may seem to
stand in need of justification, in view of the attacks on the reliability of sense
experience contained in the first and sixth of Descartes’s Meditations, and in fact
Spinoza attempts to provide this. What he says is that we may not doubt of
experience ‘after having shown that the human body as we sense it exists’.
Spinoza is in effect saying that sense experience may not be doubted once it has
been backed up by sound science and sound metaphysics, that is, once we realize
that sense experience is the expression in the attribute of thought of that which,
in the attribute of extension, consists of causal processes involving the
percipient’s body and the external world. 79
What Spinoza says about imagination, and in particular what he says about
sense experience, is important in that it serves to correct the impression that he
believes that human beings, in their search for knowledge, could in principle
proceed in a purely a priori way, in the sense that all they have to do is to deduce
consequences from definitions and axioms. The passage just quoted, in which
Spinoza supports his postulates by an appeal to sense experience, shows that this
is not so, and this is confirmed by an early letter (Ep 10, c. March 1663). In this,
Spinoza says that we need experience in the case of those things ‘which cannot
be inferred from the definition of a thing, as e.g. the existence of modes’. What he
seems to mean is that (say) the true proposition that there is a pen in front of me
is something that cannot be established by deductive means; if its truth is to be
known, it can only be by means of sense experience. Spinoza, then, is not
advocating arm-chair science; for him, experience has an important part to play
in the acquisition of knowledge. At the same time, however, he would insist that,
if we are to obtain the explanations that we seek, we must be able to place the
data of experience within the context of a deductive system, whose axioms are
self-evident.
The second and third kinds of knowledge—‘reason’ and ‘intuitive
knowledge’—are said to involve adequate ideas (Ethics, Pt II, Proposition 41).
This means that (unlike imagination) they do not present us with conclusions
that are cut off from their premises. In the case of ‘reason’, Spinoza says that it is
the kind of knowledge that we have when we possess ‘common notions and
adequate ideas of the properties of things’, and derive valid conclusions from