We can, at all events, say what (according to common sense) things are _not_. They are more than collections of aspects. If we could simultaneously perceive a “thing” at a thousand different distances, at a thousand different angles, under a thousand varieties of illumination, with its interior ideally exposed in a thousand different sections, common sense, if pressed, would, I suppose, still hold that these were no more than specimens of the endless variety of ways in which things may appear, without either changing their nature or fully revealing what that nature is. But though common sense might give this answer, it would certainly resent the question being put. It finds no difficulty in carrying on its work without starting these disturbing inquiries. It is content to say that, though a thing is doubtless always more than the sum of those aspects of it to which we happen to be attending, yet our knowledge _that_ it is and _what_ it is, however imperfect, is, for practical purposes, sufficiently clear and trustworthy, requiring the support neither of metaphysics nor psychology.—This, with all its difficulties, is, I believe, an account, true as far as it goes, of the world of things as common sense conceives it. This is the sort of world which science sets out to explain. Let me give an illustration. We perceive some object—let us say the sun. We perceive it directly and not symbolically. What we see is not a mental image of the sun, nor a complex of sensations caused by the sun; but the sun itself. Moreover, this material external object retains its identity while it varies in appearance. It is red in the morning; it is white at midday; it is red once more in the evening; it may be obscured by clouds or hidden in eclipse; it vanishes and reappears once in every twenty-four hours; yet, amid all these changes and vanishings, its identity is unquestioned. Though we perceive it differently at different times, and though there are times when we do not perceive it at all, we know it to be the same; nor do we for a moment believe (with Heraclitus) that when it is lost to view it has, on that account, either altered its character or ceased to exist.