ine in
this lecture.

I will state at the outset the view which I shall aim at establishing.
I believe that the stuff of our mental life, as opposed to its relations
and structure, consists wholly of sensations and images. Sensations are
connected with matter in the way that I tried to explain in Lecture V,
i.e. each is a member of a system which is a certain physical object.
Images, though they USUALLY have certain characteristics, especially
lack of vividness, that distinguish them from sensations, are not
INVARIABLY so distinguished, and cannot therefore be defined by these
characteristics. Images, as opposed to sensations, can only be defined
by their different causation: they are caused by association with a
sensation, not by a stimulus external to the nervous system--or perhaps
one should say external to the brain, where the higher animals are
concerned. The occurrence of a sensation or image does not in itself
constitute knowledge but any sensation or image may come to be known
if the conditions are suitable. When a sensation--like the hearing of a
clap of thunder--is normally correlated with closely similar sensations
in our neighbours, we regard it as giving knowledge of the external
world, since we regard the whole set of similar sensations as due to
a common external cause. But images and bodily sensations are not so
correlated. Bodily sensations can be brought into a correlation by
physiology, and thus take their place ultimately among sources of
knowledge of the physical world. But images cannot be made to fit in
with the simultaneous sensations and images of others. Apart from their
hypothetical causes in the brain, they have a causal connection
with physical objects, through the fact that they are copies of past
sensations; but the physical objects with which they are thus connected
are in the past, not in the present. These images remain private in
a sense in which sensations are not. A sensation SEEMS to give us
knowledge of a present physical object, while an image does not, except
when it amounts to a hallucination, and in this case the seeming is
deceptive. Thus the whole context of the two occurrences is different.
But in themselves they do not differ profoundly, and there is no reason
to invoke two different ways of knowing for the one and for the other.
Consequently introspection as a separate kind of knowledge disappears.

The criticism of introspection has been in the main the work of American