252 Public Lectures
Locke’s argument on behalf of the causal theory of percep-
tion. Indeed, it was beginning with that phase of perception
which is least likely to prove his point.1 For example, you
are much more likely to get away with the assertion that the
taste of an apple is just a sensation in you, than with the
assertion that the red apparently on its surface is just a sen-
sation in you. There is something objective about color
which is wanting in sounds, smells, tastes, and sensations of
temperature and pain. A pain or a taste may pretty safely
be said to be where the body is, but are not colors at a dis-
tance from the eye ? It is fairly reasonable to say that an
apple is sweet and cool only in contact with some palate,
but is it as reasonable to say that the apple is red only in
contact with some eye? Certainly, Locke would answer, and
it is reasonable for the same reasons, because in both cases
there are in the real apple only certain atoms and aggregates
of atoms in motion which directly or indirectly strike upon
the sense-organs to produce sensations in the mind. Red is a
sensation, like taste or pain. If a steel wedge were driven
into the palm of your hand, would you say that the resultant
pain is in the steel, a quality of the steel, like its solidity?
If not, why say that the gray-blue sensation you experience
when the wedge operates upon your eye is in the steel ? There
is, if you will, a slight difference in the two cases, for in the
case of pain, the actual bulk of the object is pressed against
the tactual organs, whereas in the case of gray-blue, the bulk
of the object is not pressed up against the eye. But it is
none the less in indirect physical contact with the eye, for
from its surface a thin regular sequence of light-particles is
being emitted to the retina, whence rises the gray-blue sensa-
tion in the mind of the observer. In short, Locke interprets
1Locke himself wrote ". . . visible species are the most difficult to be
explained by material causes.” Wks. Vol. IX, p. 215.