He merely gives us a fuller and a more exact account than was before within our reach of the space relations which obtain in the world of external objects, a world we already know pretty well.
Suppose that we say to him: You have spent many years in dividing up space and in scrutinizing the relations that are to be discovered in that realm; now tell us, what is space?
Is it real?
Is it a thing, or a quality of a thing, or merely a relation between things?
And how can any man think space, when the ideas through which he must think it are supposed to be themselves non-extended?
The space itself is not supposed to be in the mind; how can a collection of non-extended ideas give any inkling of what is meant by extension?
Would any teacher of mathematics dream of discussing these questions with his class before proceeding to the proof of his propositions?
It is generally admitted that, if such questions are to be answered at all, it is not with the aid of geometrical reasonings that they will be answered.
10.

THE SCIENCE OF PSYCHOLOGY .-- Now let us come back to a science which has to do directly with things.

We have seen that the plain man has some knowledge of minds as well as of material things.

Every one admits that the psychologist knows minds better.

May we say that his knowledge of minds differs from that of the plain man about as the knowledge of plants possessed by the botanist differs from that of all intelligent persons who have cared to notice them?
Or is it a knowledge of a quite different kind?
Those who are familiar with the development of the sciences within recent years have had occasion to remark the fact that psychology has been coming more and more to take its place as an independent science.
Formerly it was regarded as part of the duty of the philosopher to treat of the mind and its knowledge; but the psychologist who pretends to be no more than a psychologist is a product of recent times.