254 Public Lectures
as we have been describing, and it simply states that there is
a space-time interval between cause and effect, such that the
yellow sensation one has on looking at Jupiter cannot be
Jupiter itself, since the sensation is effect and Jupiter cause.
Admit causation between external object and sensation, and
thereafter you cannot say that what is directly sensed is
identical with its cause in another part of the universe.
We seem now, with Locke, to have shown that a sensation
is one thing, and the outer cause of it another. This estab-
lishes, on a causal basis, the dualistic or indirect theory of
perception. But, having revealed the width and depth of the
mote between sensation and outer cause, we find ourselves
faced with the necessity of explaining how experience bridges
this gap. After all, to show that all immediate sensations are
in the mind, is not to show how knowledge occurs about
things outside the mind. Merely seeing a thing in the mind
is not knowing anything of the nature of say a real chair or
table, such that if we do know things like real chairs and
tables, we have yet to explain the nature of this knowledge.
This brings us to another important aspect of Locke’s view,
namely, what is called the representative theory of percep-
tion. The kernel of this thesis is well brought out by turning
to Locke’s definitions of “idea” and “quality.”
We have seen how, though the characteristic of the mind
is to be active or to operate upon things, it can allow itself
to be passively operated upon by things. It is at this point
of the mind’s lending itself to be operated upon that sensa-
tion occurs. The part of the mind that is most intimately
united to the body is itself capable of being causally affected
by the motions in the sense-organs. One might almost say
that in thus becoming passive, the mind acquires a kind of
materiality in order to become capable of being moved by
matter. That is, if mind did not here tend towards becoming