With this view the idealist will be in agreement; his objection is of a different kind. He rejects, as the pragmatist does, the notion of a reality independent of human nature that forces upon us the changes that our conceptions undergo. These changes, he holds, are the inner working of the conceptions themselves, the manifestation of our intellectual nature, ever striving for an ideal of logical consistency. Truth is this ideal. We do not make it; we move towards it. If we compare, then, the idealist and the pragmatist doctrine, it will seem that, while for the idealist truth is growing with advancing knowledge into an ever larger because more comprehensive system of reality, for the pragmatist it is ever narrowing, discarding failures as useless and irrelevant to present purpose. How indeed, the idealist will ask, if practical consequences be the meaning of truth, is it possible to understand that knowledge has advanced or can advance? Does not the history of science prove a continual expansion, an increasing { 53} comprehension? It is within the conception that the inconsistency is revealed, not in any mere outward use of the conceptions, and the intellectual effort is to reconcile the contradiction by relating the conception to a more comprehensive whole. How, then, does the idealist meet this case which we have specially instanced, the demand for new notions of space and time made by the Principle of Relativity? He denies that the new conceptions are called forth by human needs in the narrow sense--that is to say, in the sense that working hypotheses or practical postulates are required. The need is purely logical. The inconsistency revealed in the notions that have hitherto served us can only be reconciled by apprehending a higher unity. If the older notions of space and time are inadequate to the more comprehensive view of the universe as a co-ordination of systems of movement, then this very negation of the older notions is the affirmation of the new, and from the negation by pure logic the content and meaning which are the truth of the new notions are derived. To this objection the pragmatist reply is that if this be the meaning of the truth there is no way shown by which it can be distinguished from error. There is in fact for idealism no error, no illusion, no falsehood; as real facts, there are only degrees of truth. But a theory of truth which ignores such stubborn realities as illusion, falsehood, and error is, from whatever standpoint we view it, useless. On the other hand, pragmatism offers a test by which we can discriminate between true and false--namely, the method of judging conceptions by their practical consequences. Can we or can we not make our conceptions work? That is the whole meaning of asking, Are they true or false? And now, lest the reader is alarmed at the prospect of having to revise his working ideas of space and { 54} time, I will, to reassure him, quote the words with which Henri Poincaré concluded his account of the new conceptions, and which admirably express and illustrate the pragmatist's attitude: "What is to be our position in view of these new conceptions? Are we about to be forced to modify our conclusions? No, indeed: we had adopted a convention because it seemed to us convenient, and we declared that nothing could compel us to abandon it. To-day certain physicists wish to adopt a new convention. It is not because they are compelled to; they judge this new convention to be more convenient--that is all; and those who are not of this opinion can legitimately keep the old and so leave their old habits undisturbed. I think, between ourselves, that this is what they will do for a long time to come."