0. REAL THINGS.--And what is this _real tree_ that we are supposed to
see as it is when we are close to it?

About two hundred years ago the philosopher Berkeley pointed out that
the distinction commonly made between things as they look, the
apparent, and things as they are, the real, is at bottom the
distinction between things as presented to the sense of sight and
things as presented to the sense of touch. The acute analysis which he
made has held its own ever since.

We have seen that, in walking towards the tree, we have a long series
of visual experiences, each of which differs more or less from all of
the others. Nevertheless, from the beginning of our progress to the
end, we say that we are looking at the same tree. The images change
color and grow larger. We do not say that the tree changes color and
grows larger. Why do we speak as we do? It is because, all along the
line, we mean by the real tree, not what is given to the sense of
sight, but something for which this stands as a sign. This something
must be given in our experience somewhere, we must be able to perceive
it under some circumstances or other, or it would never occur to us to
recognize the visual experiences as _signs_, and we should never say
that in being conscious of them in succession we are looking at the
same tree. They are certainly not the same with each other; how can we
know that they all stand for the same thing, unless we have had
experience of a connection of the whole series with one thing?

This thing for which so many different visual experiences may serve as
signs is the thing revealed in experiences of touch. When we ask: In
what direction is the tree? How far away is the tree? How big is the
tree? we are always referring to the tree revealed in touch. It is
nonsense to say that _what we see_ is far away, if by what we see we
mean the visual experience itself. As soon as we move we lose that
visual experience and get another, and to recover the one we lost we
must go back where we were before. When we say we see a tree at a
distance, we must mean, then, that we know from certain visual
experiences which we have that by moving a certain distance we will be
able to touch a tree. And what does it mean to move a certain
distance? In the last analysis it means to us to have a certain
quantity of movement sensations.

Thus the real world of things, for which experiences of sight serve as
signs, is a world revealed in