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.