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