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 extension with a real mathematical point, and call the tree nonextended in this sense. If we do this we are still in the old error—we have not gotten away from real space, but have substituted position in that space for extension in that space. Nothing mental can have even a position in real space. To do that it would have to be a real thing in the sense indicated.
Let us, then, agree with the plain man in affirming that the mind is nonextended, but let us avoid misconception. The mind is constituted of experiences of the subjective order. None of these are in space—real space. But some of them have apparent extension, and we must not overlook all that this implies.
Now for the mind as immaterial. We need not delay long over this point. If we mean by the mind the phenomena of the subjective order, and by what is material the phenomena of the objective order, surely we may and must say that the mind is immaterial. The two classes of phenomena separate themselves out at once.
[1] "The Passions," Articles 34 and 42.