the same as what we immediately experience by sight or touch or
hearing. The real table, if there is one, is not _immediately_ known
to us at all, but must be an inference from what is immediately known.
Hence, two very difficult questions at once arise; namely, (1) Is
there a real table at all? (2) If so, what sort of object can it be?

It will help us in considering these questions to have a few simple
terms of which the meaning is definite and clear. Let us give the
name of 'sense-data' to the things that are immediately known in
sensation: such things as colours, sounds, smells, hardnesses,
roughnesses, and so on. We shall give the name 'sensation' to the
experience of being immediately aware of these things. Thus, whenever
we see a colour, we have a sensation _of_ the colour, but the colour
itself is a sense-datum, not a sensation. The colour is that _of_
which we are immediately aware, and the awareness itself is the
sensation. It is plain that if we are to know anything about the
table, it must be by means of the sense-data--brown colour, oblong
shape, smoothness, etc.--which we associate with the table; but, for
the reasons which have been given, we cannot say that the table is the
sense-data, or even that the sense-data are directly properties of the
table. Thus a problem arises as to the relation of the sense-data to
the real table, supposing there is such a thing.

The real table, if it exists, we will call a 'physical object'. Thus
we have to consider the relation of sense-data to physical objects.
The collection of all physical objects is called 'matter'. Thus our
two questions may be re-stated as follows: (1) Is there any such thing
as matter? (2) If so, what is its nature?

The philosopher who first brought prominently forward the reasons for