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