becomes universal when it exists alongside of the more
specific images of its instances, and is knowingly contrasted with them.
In this case we find again, as we found when we were discussing words
in general in the preceding lecture, that images are not logically
necessary in order to account for observable behaviour, i.e. in this
case intelligent speech. Intelligent speech could exist as a motor
habit, without any accompaniment of images, and this conclusion applies
to words of which the meaning is universal, just as much as to words of
which the meaning is relatively particular. If this conclusion is valid,
it follows that behaviourist psychology, which eschews introspective
data, is capable of being an independent science, and of accounting
for all that part of the behaviour of other people which is commonly
regarded as evidence that they think. It must be admitted that this
conclusion considerably weakens the reliance which can be placed upon
introspective data. They must be accepted simply on account of the
fact that we seem to perceive them, not on account of their supposed
necessity for explaining the data of external observation.

This, at any rate, is the conclusion to which we are forced, so long
as, with the behaviourists, we accept common-sense views of the physical
world. But if, as I have urged, the physical world itself, as known,
is infected through and through with subjectivity, if, as the theory
of relativity suggests, the physical universe contains the diversity of
points of view which we have been accustomed to regard as distinctively
psychological, then we are brought back by this different road to the
necessity for trusting observations which are in an important sense
private. And it is the privacy of introspective data which causes much
of the behaviourists' objection to them.

This is an example of the difficulty of constructing an adequate
philosophy of any one science without taking account of other sciences.
The behaviourist philosophy of psychology, though in many respects
admirable from the point of view of method, appears to me to fail in
the last analysis because it is based upon an inadequate philosophy of
physics. In spite, therefore, of the fact that the evidence for images,
whether generic or particular, is merely introspective, I cannot
admit that images should be rejected, or that we should minimize their
function in our knowledge of what is remote in time or space.

LECTURE