no means an easy matter.
For our purposes, it is not important to determine what exactly is the
sensational core in any case; it is only important to notice that
there certainly is a sensational core, since habit, expectation and
interpretation are diversely aroused on diverse occasions, and the
diversity is clearly due to differences in what is presented to
the senses. When you open your newspaper in the morning, the actual
sensations of seeing the print form a very minute part of what goes
on in you, but they are the starting-point of all the rest, and it
is through them that the newspaper is a means of information or
mis-information. Thus, although it may be difficult to determine what
exactly is sensation in any given experience, it is clear that there is
sensation, unless, like Leibniz, we deny all action of the outer world
upon us.

Sensations are obviously the source of our knowledge of the world,
including our own body. It might seem natural to regard a sensation as
itself a cognition, and until lately I did so regard it. When, say, I
see a person I know coming towards me in the street, it SEEMS as
though the mere seeing were knowledge. It is of course undeniable that
knowledge comes THROUGH the seeing, but I think it is a mistake to
regard the mere seeing itself as knowledge. If we are so to regard it,
we must distinguish the seeing from what is seen: we must say that, when
we see a patch of colour of a certain shape, the patch of colour is one
thing and our seeing of it is another. This view, however, demands the
admission of the subject, or act, in the sense discussed in our first
lecture. If there is a subject, it can have a relation to the patch of
colour, namely, the sort of relation which we might call awareness. In
that case the sensation, as a mental event, will consist of awareness of
the colour, while the colour itself will remain wholly physical, and
may be called the sense-datum, to distinguish it from the sensation.
The subject, however, appears to be a logical fiction, like mathematical
points and instants. It is introduced, not because observation reveals
it, but because it is linguistically convenient and apparently demanded
by grammar. Nominal entities of this sort may or may not exist, but
there is no good ground for assuming that they do. The functions that
they appear to perform can always be performed by classes or series or
other logical constructions, consisting of less dubious entities.