Locke’s Theory of Perception 257
qualities of objects in nature. And this view, that certain
elements in the mind signify or stand for elements in nature,
is the representative theory of perception. Besides resem-
blance, however, Locke must mention something else to
answer the question, why did it ever occur to the mind that
there is, entirely outside it, a world of objects which in cer-
tain respects are like its ideas? After all, if everything di-
rectly experienced is in the mind, what could have ever
suggested to this mind that there is a whole real world out-
side it, even though there may be resemblance ? A good part
of our belief in the existence of an external world, Locke
answers, rises out of the feeling we have of “actually re-
ceiving”1 stimuli from an external non-mental source. That
is to say, over and above merely having ideas that happen to
resemble material properties in certain respects, we also have
an indefeasible sense that something is continually approach-
ing the mind from without, to make contact with it, and to
cause or produce in it its sensations. Our sensations are ex-
perienced as effects, and that is sufficient in itself to prove
the existence of their external causes. It is a feeling that if
we could really get outside of our minds and follow this
causal sequence back out into nature, we would eventually
arrive at the material object which is the source of stimula-
tion. The inference of its extramental existence is not a blind
or irrational one. Locke says we have unquestionable sensory
evidence at least of the existence of things outside our minds,
though of the precise nature of these things we may be com-
paratively ignorant. That such sensory evidence however is
really quite questionable, contrary to Locke’s belief, is shown
by the sceptical development his theory of knowledge under-
went in the hands of Berkely and Hume, who concluded that,
for all we know, nothing exists outside of mind.
ɪ ɪv, 2, 14, and ɪv, ɪɪ, 2.