The Problems of Philosophy | Page 6

whom we call ' I'. So far as immediate certainty goes, it
might be that the something which sees the brown colour is quite momentary, and not the
same as the something which has some different experience the next moment.
Thus it is our particular thoughts and feelings that have primitive certainty. And this
applies to dreams and hallucinations as well as to normal perceptions: when we dream or
see a ghost, we certainly do have the sensations we think we have, but for various reasons
it is held that no physical object corresponds to these sensations. Thus the certainty of our
knowledge of our own experiences does not have to be limited in any way to allow for
exceptional cases. Here, therefore, we have, for what it is worth, a solid basis from which
to begin our pursuit of knowledge.
The problem we have to consider is this: Granted that we are certain of our own
sense-data, have we any reason for regarding them as signs of the existence of something
else, which we can call the physical object? When we have enumerated all the sense-data
which we should naturally regard as connected with the table, have we said all there is to
say about the table, or is there still something else--something not a sense-datum,
something which persists when we go out of the room? Common sense unhesitatingly
answers that there is. What can be bought and sold and pushed about and have a cloth
laid on it, and so on, cannot be a mere collection of sense-data. If the cloth completely

hides the table, we shall derive no sense-data from the table, and therefore, if the table
were merely sense-data, it would have ceased to exist, and the cloth would be suspended
in empty air, resting, by a miracle, in the place where the table formerly was. This seems
plainly absurd; but whoever wishes to become a philosopher must learn not to be
frightened by absurdities.
One great reason why it is felt that we must secure a physical object in addition to the
sense-data, is that we want the same object for different people. When ten people are
sitting round a dinner-table, it seems preposterous to maintain that they are not seeing the
same tablecloth, the same knives and forks and spoons and glasses. But the sense-data are
private to each separate person; what is immediately present to the sight of one is not
immediately present to the sight of another: they all see things from slightly different
points of view, and therefore see them slightly differently. Thus, if there are to be public
neutral objects, which can be in some sense known to many different people, there must
be something over and above the private and particular sense-data which appear to
various people. What reason, then, have we for believing that there are such public
neutral objects?
The first answer that naturally occurs to one is that, although different people may see the
table slightly differently, still they all see more or less similar things when they look at
the table, and the variations in what they see follow the laws of perspective and reflection
of light, so that it is easy to arrive at a permanent object underlying all the different
people's sense-data. I bought my table from the former occupant of my room; I could not
buy his sense-data, which died when he went away, but I could and did buy the confident
expectation of more or less similar sense-data. Thus it is the fact that different people
have similar sense-data, and that one person in a given place at different times has similar
sense-data, which makes us suppose that over and above the sense-data there is a
permanent public object which underlies or causes the sense-data of various people at
various times.
Now in so far as the above considerations depend upon supposing that there are other
people besides ourselves, they beg the very question at issue. Other people are
represented to me by certain sense-data, such as the sight of them or the sound of their
voices, and if I had no reason to believe that there were physical objects independent of
my sense-data, I should have no reason to believe that other people exist except as part of
my dream. Thus, when we are trying to show that there must be objects independent of
our own sense-data, we cannot appeal to the testimony of other people, since this
testimony itself consists of sense-data, and does not reveal other people's experiences
unless our own sense-data are signs of things existing independently of us. We must
therefore, if possible, find, in our own purely private experiences, characteristics which
show, or tend to show, that there are in the world things other than ourselves