Philosophy

merely giving, by anticipation, the reasons for regarding perception as a form of reaction to the environment, displayed in some bodily movement, rather than as a form of knowledge. When we have considered further what constitutes knowledge, we may find that perception is, after all, a form of knowledge, but only because knowledge is not quite what we naturally suppose it to be. For the present, let us stick to the view of perception that can be obtained by the external observer, i.e. as something displayed in the manner of reacting to the environment. From the point of view of the external observer, perception is established just like any other causal correlation. We observe that, whenever a certain object stands in a certain spatial relation to a man’s body, the man’s body makes a certain movement or set of movements; we shall then say that the man “perceives” the object. So the new-born baby turns its eyes slowly towards a bright light which is not in the centre of the field of vision; this entitles us to say that the baby “perceives” the light. If he is blind, his eyes do not move in this way. A bird flying about in a wood does not bump into the branches, whereas in a room it will bump into the glass of the window. This entitles us to say that the bird perceives the branches but not the glass. Do we “perceive” the glass or do we merely know that it is there? This question introduces us to the complications produced by association. We know by experience, from the sense of touch, that there is usually glass in window-frames; thus it makes us react to the window-frames as if we could see the glass. But sometimes there is no glass, and still we shall perhaps behave as if there were. If this can happen, it shows that we do not perceive the glass, since our reaction is the same whether there is glass or not. If, however, the glass is coloured, or slightly distorting, or not perfectly clean, a person accustomed to glass will be able to distinguish a frame containing glass from one which has none. In that case it is more difficult to decide whether we are to say that he “perceives” the glass or not. It is certain that perception is affected by experience. A person who can read perceives print where another would not. A musician perceives differences between notes which to an untrained ear are indistinguishable. People unaccustomed to the telephone cannot understand what they hear in it; but this is perhaps not really a case in point. The difficulty we are considering arises from the fact that a human body, unlike a scientific instrument, is perpetually changing its reaction to a given stimulus, under the influence of the law of association. Moreover, the human body is always doing something. How, then, are we to know whether what it is doing is the result of a given stimulus or not? In most cases, however, this difficulty is not very serious, particularly when we are dealing with people old enough to speak. When you go to the oculist he asks you to read a number of letters growing gradually smaller; at some point you fail. Where you have succeeded, he knows that you have perceived enough to make out what letter it is. Or you take a pair of compasses and press the points into a man’s back, asking him if he feels two pricks or only one. He may say one when the two points are near together; if he is on his guard against this error he may say two when in fact there is only one. But if the points are sufficiently far apart he will never make a mistake. That is to say, the bodily movement consisting in pronouncing the word “two” will invariably result from a certain stimulus. (Invariably, I mean, for a given subject on a given day.) This entitles us to say that the man can perceive that there are two points provided they are not too near together. Or you say: “What can you see on the horizon?” One man says, “I see a ship”. Another says, “I see a steamer with two funnels”. A third says, “I see a Cunarder going from Southampton to New York”. How much of what these three people say is to count as perception? They may all three be perfectly right in what they say, and yet we should not concede that a man can “perceive” that the ship is going from Southampton to New York. This, we should say, is inference. But it is by no means easy to draw a line; some things which are, in an important sense, inferential, must be admitted to be perceptions. The man who says “I see a ship” is using inference. Apart from experience, he only sees a queerly shaped dark dot on a blue background. Experience has taught him that that sort of dot “means” a ship; that is to say, he has a conditioned reflex which causes him to utter, aloud or to himself, the word “ship” when his eye is stimulated in a certain way. To disentangle what is due to experience, and what not, in the perceptions of an adult, is a hopeless task. Practically, if a word comes without previous verbal intermediaries, the ordinary man would include what the word means in the perception, while he would not do so if the man arrives at the word after verbal preliminaries, overt or internal. But this is itself a question of familiarity. Show a child a pentagon, and he will have to count the sides to know how many there are; but after a little experience of geometrical figures, the word “pentagon” will arise without any previous words. And in any case such a criterion is theoretically worthless. The whole affair is a matter of degree, and we cannot draw any sharp line between perception and inference. As soon as this is realised, our difficulties are seen to be purely verbal and therefore unimportant. It will be observed that we are not attempting at present to say what constitutes perception, but only what kind of behaviour on the part of a person whom we are observing will justify us in saying that he has perceived this or that feature of his environment. I suggest that we are justified in saying that a man “perceives” such a feature if, throughout some such period as a day, there is some bodily act which he performs whenever that feature is present, but not at any other time. This condition is clearly sufficient, but not necessary—that is to say, there may be perception even when it is not fulfilled. A man’s reaction may change through conditioning, even in so short a period as a day. Again, there may be a reaction, but one which is too slight to be observable; in this case the criterion of perception is theoretically satisfied, but not practically, since no one can know that it is. We often have evidence later on that something was perceived, although at the moment there was no discoverable reaction. I have frequently known children repeat afterwards some remark which, at the time, they seemed not to have heard. This sort of case affords another kind of evidence of perception, namely, the evidence afforded by a delayed response. Some people will sit silent and impassive in a company of talkers, giving no evidence that they are listening; yet they may go home and write down the conversation verbatim in their journals. These are the typical writers of memoirs. More remarkable still, I know one man—a man of genius, it is true—who talks incessantly, who yet, after meeting a total stranger, knows exactly what the stranger would have said if he had been given the chance. How this is managed, I do not know; but such a man is rightly called “perceptive”. Obviously, in dealing with human beings old enough to talk, words afford the best evidence of perception. A man’s verbal responses to perceptive situations do not change much after the first few years of life. If you see a kingfisher, and at the same moment your companion says “there’s a kingfisher”, that is pretty conclusive evidence that he saw it. But, as this case illustrates, our evidence that some one else has perceived something always depends upon our own perceptions. And our own perceptions are known to us in a different way from that in which the perceptions of others are known to us. This is one of the weak spots in the attempt at a philosophy from the objective standpoint. Such a philosophy really assumes knowledge as a going concern, and takes for granted the world which a man derives from his own perceptions. We cannot tackle all our philosophical problems by the objective method, but it is worth while to proceed with it as far as it will take us. This whole question of perception will have to be attacked afresh from a different angle, and we shall then find reason to regard the behaviouristic standpoint as inadequate, though valid so far as it goes. We have still, however, a long road to go before we shall be driven to consider the subjective standpoint; more particularly, we have to define “knowledge” and “inference” behaviouristically, and then, making a new start, to consider what modern physics makes of “matter”. But for the moment there are still some things to be said about perception from the objective standpoint. It will be seen that, according to our criterion of perception, an object perceived need not be in contact with the percipient’s body. The sun, moon, and stars are perceived according to the above criterion. In order, however, that an object not in contact with the body should be perceived, there are physical as well as physiological conditions to be fulfilled. There must be some physical process which takes place at the surface of the body when the object in question is suitably situated, but not otherwise; and there must be sense-organs capable of being affected by such a process. There are, as we know from physics, many processes which fulfil the necessary physical conditions, but fail to affect us through the inadequacy of our sense-organs. Waves of a certain sort make sound, but waves of exactly the same sort become inaudible if they are too short. Waves of a certain sort make light, but if they are too long or too short they are invisible. The waves used in wireless are of the same sort as those that make light, but are too long. There is no reason a priori why we should not be aware of wireless messages through our senses, without the need of instruments. X-rays are also of the same sort as those that make light, but in this case they are too short to be seen. They might render the objects from which they come visible, if we had a different sort of eye. We are not sensitive to magnetism, unless it is enormously powerful; but if we had more iron in our bodies, we might have no need of the mariner’s compass. Our senses are a haphazard selection of those that the nature of physical processes renders possible; one may suppose that they have resulted from chance variation and the struggle for existence. It is important to observe that our perceptions are very largely concerned with form or shape or structure. This is the point emphasised by what is called “Gestaltpsychologie”, or psychology of form. Reading is a case in point. Whether we read black letters on white paper or white letters on a blackboard is a matter which we hardly notice; it is the forms of the letters that affect us, not their colour or their size (so long as they remain legible). In this matter,