[LECTURE VI]
PERCEPTION, COMMON SENSE, AND SCIENCE
I
Nothing would seem easier, at first sight, than to give a general description of the ordinary beliefs of ordinary people about our familiar world of things and persons. It is the world in which we live; it is for all men a real world; it is for many men the real world; it is the world of common sense, the world where the plain man feels at home, and where the practical man seeks refuge from the vain subtleties of metaphysics. Our stock of beliefs about it may perhaps be difficult to justify, but it seems strange that they should be difficult to describe; yet difficult, I think, they are.
Some statements about it may, however, be made with confidence. It is in space and time; i.e. the material things of which it is composed, including living bodies, are extended, have mutual position, and possess at least some measure of duration.
Things are not changed by a mere change of place, but a change of place relative to an observer always changes their appearance for him. Common sense is, therefore, compelled in this, as in countless other cases, to distinguish the appearance of a thing from its reality; and to hold, as an essential article of its working creed, that appearances may alter, leaving realities unchanged.
Common sense does not, however, draw the inference that our experiences of material things is other than direct and immediate. It has never held the opinion—or, if you will, the heresy—that what we perceive (at least by sight and touch) are states of our own mind, which somehow copy or represent external things. Neither has it ever held that the character or duration of external things in any way depends upon our observations of them. In perception there is no reaction by the perceiving mind on the object perceived. Things in their true reality are not affected by mere observation, still less are they constituted by it. When material objects are in question, common sense never supposes that esse and percipi are identical.
But then, what, according to common sense, are things in their true reality? What are they “in themselves,” when no one is looking at them, or when only some of their aspects are under observation?
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.