al phenomena constitute the things which belong to the
external world?

He who says this says no more than that the mind is known and is
knowable. It is what it is perceived to be; and the more we know of
mental phenomena, the more do we know of the mind. Shall we call the
mind as thus known a _substance_? That depends on the significance
which we give to this word. It is better, perhaps, to avoid it, for it
is fatally easy to slip into the old use of the word, and then to say,
as men have said, that we do not know the mind as it is, but only as it
appears to us to be--that we do not know the reality, but only its
appearances.

And if we keep clearly before us the view of the mind which I am
advocating, we shall find an easy way out of the difficulties that seem
to confront us when we consider it as nonextended and immaterial.

Certain complexes of mental phenomena--for example, the barber's pole
above alluded to--certainly appear to be extended. Are they really
extended? If I imagine a tree a hundred feet high, is it really a
hundred feet high? Has it any real size at all?

Our problem melts away when we realize what we mean by this "real
size." In Chapter V, I have distinguished between apparent space and
real space. Real space is, as was pointed out, the "plan" of the real
physical world. To occupy any portion of real space, a thing must be a
real external thing; that is, the experiences constituting it must
belong to the objective order, they must not be of the class called
mental. We all recognize this, in a way. We know that a real material
foot rule cannot be applied to an imaginary tree. We say, How big did
the tree seen in a dream _seem_; we do not say, How big was it
_really_? If we did ask such a question, we should be puzzled to know
where to look for an answer.

And this for a very good reason. He who asks: How big was that
imaginary tree really? asks, in effect: How much real space did the
unreal tree fill? The question is a foolish one. It assumes that
phenomena not in the objective order are in the objective order. As
well ask how a color smells or how a sound looks. When we are dealing
with the material we are not dealing with the mental, and we must never
forget this.

The tree imagined or seen in a dream seems extended. Its extension is
_apparent_ extension, and this apparent extension has no place in the
external world whatever. But we must not confound this apparent
exte