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 and our private experiences.

In one sense it must be admitted that we can never prove the existence
of things other than ourselves and our experiences. No logical absurdity
results from the hypothesis that the world consists of myself and my
thoughts and feelings and sensations, and that everything else is mere
fancy. In dreams a very complicated world may seem to be present, and
yet on waking we find it was a delusion; that is to say, we find that
the sense-data in the dream do not appear to have corresponded with such
physical objects as we should naturally infer from our sense-data. (It
is true that, when the physical world is assumed, it is possible to
find physical causes for the sense-data in dreams: a door banging, for
instance, may