Philosophy

It will be remembered that we regarded perception, in Chapter V, as a species of “sensitivity”. Sensitivity to a given feature of the environment we defined as consisting in some characteristic reaction which is exhibited whenever that feature is present, but not otherwise; this property is possessed more perfectly, in given directions, by scientific instruments than by living bodies, though scientific instruments are more selective as to the stimuli to which they will respond. We decided that what, from the standpoint of an external observer, distinguishes perception from other forms of sensitivity is the law of association or conditioned reflexes. But we also found that this purely external treatment of perception presupposes our knowledge of the physical world as a going concern. We have now to investigate this presupposition, and to consider how we come to know about physics, and how much we really do know.

According to the theory of Chapter V, it is possible to perceive things that are not in a spatial contact with the body. There must be a reaction to a feature of the environment, but that feature may be at a greater or less distance from the body of the percipient; we can even perceive the sun and stars, within the limits of the definition. All that is necessary is that our reaction should depend upon the spatial relation between our body and the feature of the environment. When our back is towards the sun, we do not see it; when our face is towards it, we do.

When we consider perception—visual or auditory—of an external event, there are three different matters to be examined. There is first the process in the outside world, from the event to the percipient’s body; there is next the process in his body, in so far as this can be known by an outside observer; lastly, there is the question, which must be faced sooner or later, whether the percipient can perceive something of the process in his body which no other observer could perceive. We will take these points in order.

If it is to be possible to “perceive” an event not in the percipient’s body, there must be a physical process in the outer world such that, when a certain event occurs, it produces a stimulus of a certain kind at the surface of the percipient’s body. Suppose, for example, that pictures of different animals are exhibited on a magic lantern to a class of children, and all the children are asked to say the name of each animal in turn. We may assume that the children are sufficiently familiar with animals to say “cat”, “dog”, “giraffe”, “hippopotamus”, etc., at the right moments. We must then suppose—taking the physical world for granted—that some process travels from each picture to the eyes of the various children, retaining throughout these journeys such peculiarities that, when the process reaches their eyes, it can in one case stimulate the word “cat” and in another the word “dog”. All this the physical theory of light provides for. But there is one interesting point about language that should be noticed in this connection. If the usual physical theory of light is correct, the various children will receive stimuli which differ greatly according to their distance and direction from the picture, and according to the way the light falls. There are also differences in their reactions, for, though they all utter the word “cat”, some say it loud, others soft, some in a soprano voice, some in a contralto. But the differences in their reactions are much less than the differences in the stimuli. This is still more the case if we consider various different pictures of cats, to all of which they respond with the word “cat”. Thus language is a means of producing responses which differ less than the stimuli do, in cases where the resemblances between the stimuli are more important to us than the differences. This fact makes us apt to overlook the differences between stimuli which produce nearly identical responses.

As appears from the above, when a number of people simultaneously perceive a picture of a cat, there are differences between the stimuli to their various perceptions, and these differences must obviously involve differences in their reactions. The verbal responses may differ very little, but even the verbal responses could be made to differ by putting more complicated questions than merely “What animal is that?” One could ask: “Can the picture be covered by your thumb-nail held at arm’s length?” Then the answer would be different according as the percipient was near the picture or far off. But the normal percipient, if left to himself, will not notice such differences, that is to say, his verbal response will be the same in spite of the differences in the stimuli.

The fact that it is possible for a number of people to perceive the same noise or the same coloured pattern obviously depends upon the fact that a physical process can travel outward from a centre and retain certain of its characteristics unchanged, or very little changed. The most notable of such characteristics is frequency in a wave-motion. That, no doubt, affords a biological reason for the fact that our most delicate senses, sight and hearing, are sensitive to frequencies, which determine colour in what we see and pitch in what we hear. If there were not, in the physical world, processes spreading out from centres and retaining certain characters practically unchanged, it would be impossible for different percipients to perceive the same object from different points of view, and we should not have been able to discover that we all live in a common world.

We come now to the process in the percipient’s body, in so far as this can be perceived by an outside observer. This raises no new philosophical problems, because we are still concerned, as before, with the perception of events outside the observer’s body. The observer, now, is supposed to be a physiologist, observing, say, what goes on in the eye when light falls upon it. His means of knowing are, in principle, exactly the same as in the observation of dead matter. An event in an eye upon which light is falling causes light-waves to travel in a certain manner until they reach the eye of the physiologist. They there cause a process in the physiologist’s eye and optic nerve and brain, which ends in what he calls “seeing what happens in the eye he is observing”. But this event, which happens in the physiologist, is not what happened in the eye he was observing; it is only connected with this by a complicated causal chain. Thus our knowledge of physiology is no more direct or intimate than our knowledge of processes in dead matter; we do not know any more about our eyes than about the trees and fields and clouds that we see by means of them. The event which happens when a physiologist observes an eye is an event in him, not on the eye that he is observing.

We come now at last to the question of self-observation, which we have hitherto avoided. I say “self-observation” rather than “introspection”, because the latter word has controversial associations that I wish to avoid. I mean by “self-observation” anything that a man can perceive about himself but that others, however situated, cannot perceive about him. What follows is only preliminary, since the subject will be discussed at length in Chapter XVI.

No one can deny that we know things about ourselves which others cannot know unless we tell them. We know when we have toothache, when we feel thirsty, what we were dreaming when we woke up, and so on. Dr. Watson might say that the dentist can know we have toothache by observing a cavity in a tooth. I will not reply that the dentist is often mistaken; this may be merely because the art of dentistry has not been sufficiently perfected. I will concede as possible, in the future, a state of odontology in which the dentist could always know whether I am feeling toothache. But even then his knowledge has a different character from mine. His knowledge is an inference, based upon the inducive law that people with such-and-such cavities suffer pain of a certain kind. But this law cannot be established by observation of cavities alone; it requires that, where these are observed, the people who have them should tell us that they feel toothache. And, more than that, they must be speaking the truth. Purely external observation can discover that people with cavities say they have toothache, but not that they have it. Saying one has toothache is a different thing from having it; if not we could cure toothache by not talking about it, and so save our dentists’ bills. I am sure the expert opinion of dentists will agree with me that this is impossible.

To this argument, however, it might be replied that having toothache is a state of the body, and that knowing I have toothache is a response to this bodily stimulus. It will be said that, theoretically, the state of my body when I have toothache can be observed by an outsider, who can then also know that I have toothache. This answer, however, does not really meet the point. When the outside observer knows that I have toothache, not only is his knowledge based upon an inductive inference, as we have already seen, but his knowledge of the inferred term, “toothache”, must be based upon personal experience. No knowledge of dentistry could enable a man to know what toothache is if he had never felt it. If, then, toothache is really a state of the body—which, at the moment, I neither affirm nor deny—it is a state of the body which only the man himself can perceive. In a word, whoever has experienced toothache and can remember it has knowledge that cannot be possessed by a man who has never experienced toothache.

Take next our knowledge of our own dreams. Dr. Watson has not, so far as I know, ever discussed dreams, but I imagine he would say something like this: In dreams, there are probably small laryngeal movements such as, if they were greater, would lead to speech; indeed, people do sometimes cry out in dreams. There may also be stimulations of the sense-organs, which produce unusual reactions owing to the peculiar physiological condition of the brain during sleep: but all these reactions must consist of small movements, which could theoretically be seen from outside, say by some elaboration of X-ray apparatus. This is all very well, but meantime it is hypothetical, and the dreamer himself knows his dreams without all this elaborate inference. Can we say that he really knows these hypothetical small bodily movements, although he thinks he knows something else? That would presumably be Dr. Watson’s position, and it must be admitted that, with a definition of “knowledge” such as we considered in Chapter VIII, such a view is not to be dismissed offhand as obviously impossible. Moreover, if we are to say the perception gives knowledge of the physical world, we shall have to admit that what we are perceiving may be quite different from what it seems to be. A table does not look like a vast number of electrons and protons, nor like trains of waves meeting and clashing. Yet this is the sort of thing a table is said to be by modern physicists. If, then, what seems to us to be just a table such as may be seen any day is really this odd sort of thing, it is possible that what seems to us to be a dream is really a number of movements in the brain.

This again is all very well, but there is one point which it fails to explain, namely, what is meant by “seeming”. If a dream or a table “seems” to be one sort of thing while it is “really” another, we shall have to admit that it really seems, and that what it seems to be has a reality of its own. Nay more, we only arrive at what it “really” is by an inference, valid or invalid, from what it seems to be. If we are wrong about the seeming, we must be doubly wrong about the reality, since the sole ground for asserting the table composed of electrons and protons is the table that we see, i.e. the “seeming” table. We must therefore treat “seeming” with respect.

Let us consider Dr. Watson watching a rat in a maze. He means to be quite objective, and report only what really goes on. Can he succeed? In one sense he can. He can use words about what he sees which are the same as any other scientifically trained observer will use if he watches the same rat at the same time. But Dr. Watson’s objectivity emphatically does not consist in using the same words as other people use; his vocabulary is very different from that of most psychologists. He cannot take as the sole test of truth the consensus of mankind. “Securus judicat orbis terrarum” is another example of a Latin tag which is false, and which certainly Dr. Watson would not consider true. It has happened again and again in human history that a man who said something that had never been said before turned out to be right, while the people who repeated the wise saws of their forefathers were talking nonsense. Therefore, when Dr. Watson endeavours to eliminate subjectivity in observing rats, he does not mean that he says what everybody else says. He means that he refrains from inferring anything about the rat beyond its bodily movements. This is all to the good, but I think he fails to realise that almost as long and difficult an inference is required to give us knowledge of the rat’s bodily movements as to give us knowledge of its “mind”. And what is more, the data from which we must start in order to get to know the rat’s bodily movements are data of just the sort that Dr. Watson wishes to avoid, namely private data patent to self-observation but not patent to anyone except the observer. This is the point at which, in my opinion, behaviourism as a final philosophy breaks down.

When several people simultaneously watch a rat in a maze, or any other example of what we should naturally regard as matter in motion, there is by no means complete identity between the physical events which happen at the surface of their eyes and constitute the stimuli to their perceptions. There are differences of perspective, of light and shade, of apparent size, and so on, all of which will be reproduced in photographs taken from the places where the eyes of the several observers are. These differences produce differences in the reactions of the observers—differences which a quite unthinking person may overlook, but which are familiar to every artist. Now it is contrary to all scientific canons to suppose that the object perceived, in addition to affecting us in the way of stimulus and reaction, also affects us directly by some mystical epiphany; certainly it is not what any behaviourist would care to assert. Our knowledge of the physical world, therefore, must be contained in our reaction to the stimulus which reaches us across the intervening medium; and it seems hardly possible that our reaction should have a more intimate relation to the object than the stimulus has. Since the stimulus differs for different observers, the reaction also differs; consequently, in all our perceptions of physical processes there is an element of subjectivity. If, therefore, physics is true in its broad outlines (as the above argument supposes), what we call “perceiving” a physical process is something private and subjective, at least in part, and is yet the only possible starting-point for our knowledge of the physical world.

There is an objection to the above argument which might naturally be made, but it would be in fact invalid. It may be said that we do not in fact proceed to infer the physical world from our perceptions, but that we begin at once with a rough-and-ready knowledge of the physical world, and only at a late stage of sophistication compel ourselves to regard our knowledge of the physical world as an inference. What is valid in this statement is the fact that our knowledge of the physical world is not at first inferential, but that is only because we take our percepts to be the physical world. Sophistication and philosophy come in at the stage at which we realise that the physical world cannot be identified with our percepts. When my boy was three years old, I showed him Jupiter, and told him that Jupiter was larger than the earth. He insisted that I must be speaking of some other Jupiter, because, as he patiently explained, the one he was seeing was obviously quite small. After some efforts, I had to give it up and leave him unconvinced. In the case of the heavenly bodies, adults have got used to the idea that what is really there can only be inferred from what they see; but where rats in mazes are concerned, they still tend to think that they are seeing what is happening in the physical world. The difference, however, is only one of degree, and naive realism is as untenable in the one case as in the other. There are differences in the perceptions of two persons observing the same process; there are sometimes no discoverable differences between two perceptions of the same persons observing different processes, e.g. pure water and water full of bacilli. The subjectivity of our perceptions is thus of practical as well as theoretical importance.

I am not maintaining that what we primarily know is our own perceptions. This is largely a verbal question; but with the definition of knowledge given in Chapter VIII, it will be correct to say that from the first we know external objects, the question is not as to what are the objects we know, but rather as to how accurately we know them. Our non-inferential knowledge of an object cannot be more accurate than our reaction to it, since it is part of that reaction. And our reaction cannot be more accurate than the stimulus. But what on earth can you mean by the “accuracy” of a stimulus? I may be asked. I mean just the same as by the accuracy of a map or a set of statistics. I mean a certain kind of correspondence. One pattern is an accurate representation of another if every element of the one can be taken as the representative of just one element of the other, and the relations that make the one set into a pattern correspond with relations making the other set into a pattern. In this sense, writing can represent speech with a certain degree of accuracy; to every spoken word a written word corresponds, and to the time-order of the spoken words the space-order of the written words corresponds. But there are inflexions and tones of voice that cannot be represented in writing, except, to some extent, by musical notation. A gramophone record is a much more accurate representation of vocal sounds than any writing can be; but even the best gramophone record fails to be completely accurate. The impression made upon an observer is very analogous to a gramophone record or a photograph, but usually less accurate owing to the influence of the law of association, and the lack of delicacy in our senses. And whatever limitations there are to the accuracy of our impressions are limitations to the accuracy of our non-inferential knowledge of the external world.

Another point: If we accept the definition of knowledge given in Chapter VIII, which was framed so far as to be as favourable as possible to behaviourism, a given reaction may be regarded as knowledge of various different occurrences. When we see Jupiter, we have, according to the definition, knowledge of Jupiter, but we also have knowledge of the stimulus at the surface of the eye, and even of the process in the optic nerve. For it is arbitrary at what point we start in the process leading to a certain event in the brain: this event, and the consequent bodily action, may be regarded as a reaction to a process starting at any earlier point. And the nearer our starting-point is to the brain, the more accurate becomes the knowledge displayed in our reaction. A lamp at the top of a tall building might produce the same visual stimulus as Jupiter, or at any rate one practically indistinguishable from that produced by Jupiter. A blow on the nose might make us “see stars”. Theoretically, it should be possible to apply a stimulus direct to the optic nerve, which should give us a visual sensation. Thus when we think we see Jupiter, we may be mistaken. We are less likely to be mistaken if we say that the surface of the eye is being stimulated in a certain way, and still less likely to be mistaken if we say that the optic nerve is being stimulated in a certain way. We do not eliminate the risk of error completely unless we confine ourselves to saying that an event of a certain sort is happening in the brain; this statement may still be true if we see Jupiter in a dream.

But, I shall be asked, what do you know about what is happening in the brain? Surely nothing. Not so, I reply. I know about what is happening in the brain exactly what naive realism thinks it knows about what is happening in the outside world. But this needs explaining, and there are other matters that must be explained first.

When the light from a fixed star reaches me, I see the star if it is night and I am looking in the right direction. The light started years ago, probably many years ago, but my reaction is primarily to something that is happening now. When my eyes are open, I see the star; when they are shut, I do not. Children discover at a fairly early age that they see nothing when their eyes are shut. They are aware of the difference between seeing and not seeing, and also of the difference between eyes open and eyes shut; gradually they discover that these two differences are correlated—I mean that they have expectations of which this is the intellectualist transcription. Again, children learn to name the colours, and to state correctly whether a thing is blue or red or yellow or what-not. They ought not to be sure that light of the appropriate wave-length started from the object. The sun looks red in a London fog, grass looks blue through blue spectacles, everything looks yellow to a person suffering from jaundice. But suppose you ask: What colour are you seeing? The person who answers, in these cases, red for the sun, blue for the grass, and yellow for the sick-room of the jaundiced patient, is answering quite truly. And in each of these cases he is stating something that he knows. What he knows in such cases is what I call a “percept”. I shall contend later that, from the standpoint of physics, a percept is in the brain; for the present, I am only concerned to say that a percept is what is most indubitable in our knowledge of the world.

To behaviourism as a metaphysic one may put the following dilemma. Either physics is valid in its main lines, or it is not. If it is not, we know nothing about the movements of matter; for physics is the result of the most serious and careful study of which the human intelligence has hitherto been capable. If, on the other hand, physics is valid in its main lines, any physical process starting either inside or outside the body will, if it reaches the brain, be different if the intervening medium is different; moreover two persons, initially very different, may become indistinguishable as they spread and grow fainter. On both grounds, what happens in the brain is not connected quite accurately with what happens elsewhere, and our perceptions are therefore infected with subjectivity on purely physical grounds. Even, therefore, when we assume the truth of physics, what we know most indubitably through perception is not the movements of matter, but certain events in ourselves which are connected, in a manner not quite invariable, with the movements of matter. To be specific, when Dr. Watson watches rats in mazes, what he knows, apart from difficult inferences, are certain events in himself. The behaviour of the rats can only be inferred by the help of physics, and is by no means to be accepted as something accurately knowable by direct observation.

I do not in fact entertain any doubts that physics is true in its main lines. The interpretation of physical formulæ is a matter as to which a considerable degree of uncertainty is possible; but we cannot well doubt that there is an interpretation which is true roughly and in the main. I shall come to the question of interpretation later; for the present, I shall assume that we may accept physics in its broad outlines, without troubling to consider how it is to be interpreted. On this basis, the above remarks on perception seem undeniable. We are often misled as to what is happening, either by peculiarities of the medium between the object and our bodies, or by unusual states of our bodies, or by a temporary or permanent abnormality in the brain. But in all these cases something is really happening, as to which, if we turn our attention to it, we can obtain knowledge that is not misleading. At one time when, owing to illness, I had been taking a great deal of quinine, I became hypersensitive to noise, so that when the nurse rustled the newspaper I thought she was spilling a scuttle of coals on the floor. The interpretation was mistaken, but it was quite true that I heard a loud noise. It is a commonplace that a man whose leg has been amputated can still feel pains in it; here again, he does really feel the pains, and is only mistaken in his belief that they come from his leg. A percept is an observable event, but its interpretation as knowledge of this or that event in the physical world is liable to be mistaken, for reasons which physics and physiology can make fairly clear.

The subjectivity of percepts is a matter of degree. They are more subjective when people are drunk or asleep than when they are sober and awake. They are more subjective in regard to distant objects than in regard to such as are near. They may acquire various peculiar kinds of subjectivity through injuries to the brain or to the nerves. When I speak of a percept as “subjective” I mean that the physiological inferences to which it gives rise are mistaken or vague. This is always the case to some extent, but much more so in some circumstances than in others. And the sort of defect that leads to mistakes must be distinguished from the sort that leads to vagueness. If you see a man a quarter of a mile away, you can see that it is a man if you have normal eyesight, but you probably cannot tell who it is, even if in fact it is some one you know well. This is vagueness in the percept: the inferences you draw are correct so far as they go, but they do not go very far. On the other hand, if you are seeing double and think there are two men, you have a case of mistake. Vagueness, to a greater or less extent, is universal and inevitable; mistakes, on the other hand, can usually be avoided by taking trouble and by not always trusting to physiological inference. Anybody can see double on purpose, by focussing on a distant object and noticing a near one; but this will not cause mistakes, since the man is aware of the subjective element in his double vision. Similarly we are not deceived by after-images, and only dogs are deceived by gramophones.

From what has been said in this chapter, it is clear that our knowledge of the physical world, if it is to be made as reliable as possible, must start from percepts, and must scrutinize the physiological inferences by which percepts are accompanied. Physiological inference is inference in the sense that it sometimes leads to error and physics gives reason to expect that percepts will, in certain circumstances, be more or less deceptive if taken as signs of something outside the brain. It is these facts that give a subjective cast to the philosophy of physics, at any rate in its beginnings. We cannot start cheerfully with a world of matter in motion, as to which any two sane and sober observers must agree. To some extent, each man dreams his own dream, and the disentangling of the dream element in our percepts is no easy matter. This is, indeed, the work that scientific physics undertakes to do.