But when we look back, and speculate as to how the common-sense categories may have achieved their wonderful supremacy, no reason appears why it may not have been by a process just like that by which the conceptions due to Democritus, Berkeley, or Darwin, achieved their similar triumphs in more recent times.  In other words, they may have been successfully discovered by prehistoric geniuses whose names the night of antiquity has covered up; they may have been verified by the immediate facts of experience which they first fitted; and then from fact to fact and from man to man they may have spread, until all language rested on them and we are now incapable of thinking naturally in any other terms.  Such a view would only follow the rule that has proved elsewhere so fertile, of assuming the vast and remote to conform to the laws of formation that we can observe at work in the small and near.

For all utilitarian practical purposes these conceptions amply suffice; but that they began at special points of discovery and only gradually spread from one thing to another, seems proved by the exceedingly dubious limits of their application to-day.  We assume for certain purposes one ‘objective’ Time that AEQUABILITER FLUIT, but we don’t livingly believe in or realize any such equally-flowing time.  ‘Space’ is a less vague notion; but ‘things,’ what are they?  Is a constellation properly a thing? or an army? or is an ens RATIONIS such as space or justice a thing?  Is a knife whose handle and blade are changed the ‘same’?  Is the ‘changeling,’ whom Locke so seriously discusses, of the human ‘kind’?  Is ‘telepathy’ a ‘fancy’ or a ‘fact’?  The moment you pass beyond the practical use of these categories (a use usually suggested sufficiently by the circumstances of the special case) to a merely curious or speculative way of thinking, you find it impossible to say within just what limits of fact any one of them shall apply.

The peripatetic philosophy, obeying rationalist propensities, has tried to eternalize the common-sense categories by treating them very technically and articulately.  A ‘thing’ for instance is a being, or ens.  An ens is a subject in which qualities ‘inhere.’  A subject is a substance.  Substances are of kinds, and kinds are definite in number, and discrete.  These distinctions are fundamental and eternal.  As terms of discourse they are indeed magnificently useful, but what they mean, apart from their use in steering our discourse to profitable issues, does not appear.  If you ask a scholastic philosopher what a substance may be in itself, apart from its being the support of attributes, he simply says that your intellect knows perfectly what the word means.