Philosophy

It will be remembered that the task upon which we are at present engaged is the definition of “knowledge” as a phenomenon discoverable by an outside observer. When we have said what we can from this objective standpoint, we will ask ourselves whether anything further, and if so what, is to be learnt from the subjective standpoint, in which we take account of facts which can only be discovered when the observer and the observed are the same person. But for the present we will resolutely confine ourselves to those facts about a human being which another human being can observe, together with such inferences as can be drawn from these facts. The word “knowledge” is very ambiguous. We say that Watson’s rats “know” how to get out of mazes, that a child of three “knows” how to talk, that a man “knows” the people with whom he is acquainted, that he “knows” what he had for breakfast this morning, and that he “knows” when Columbus first crossed the ocean. French and German are less ambiguous, since each has two words for different kinds of “knowing”, which we tend to confuse in our thoughts because we confuse them in our language. I shall not attempt as yet to deal with knowledge in general, but rather with certain less general concepts which would ordinarily be included under “knowledge”. And first of all I will deal with perception—not as it appears to the perceiver, but as it can be tested by an outside observer. Let us try, first, to get a rough preliminary view of the sort of thing we are going to mean by “perception”. One may say that a man “perceives” anything that he notices through his senses. This is not a question of the sense-organs alone, though they are a necessary condition. No man can perceive by sight what is not in his field of vision, but he may look straight at a thing without perceiving it. I have frequently had the experience—supposed to be characteristic of philosophers—of looking everywhere for my spectacles although they were before my eyes when my search began. We cannot therefore tell what a man is perceiving by observing his sense-organs alone, though they may enable us to know that he is not perceiving something. The observer can only know that a man is perceiving something if the man reacts in some appropriate manner. If I say to a man “please pass the mustard” and he thereupon passes it, it is highly probable that he perceived what I said, although it may of course be a mere coincidence that he passed it at that moment. But if I say to him “the telephone number you want is 2467” and he proceeds to call that number, the odds against his doing so by mere chance are very great—roughly 10,000 to 1. And if a man reads aloud out of a book, and I look over his shoulder and perceive the same words, it becomes quite fantastic to suppose that he does not perceive the words he is uttering. We can thus in many cases achieve practical certainty as to some of the things that other people are perceiving. Perception is a species of a wider genus, namely sensitivity. Sensitivity is not confined to living things; in fact it is best exemplified by scientific instruments. A material object is said to be “sensitive” to such and such a stimulus, if, when the stimulus is present, it behaves in a way noticeably different from that in which it behaves in the absence of the stimulus. A photographic plate is sensitive to light, a barometer is sensitive to pressure, a thermometer to temperature, a galvanometer to electric current, and so on. In all these cases, we might say, in a certain metaphorical sense, that an instrument “perceives” the stimulus to which it is sensitive. We do not in fact say so; we feel that perception involves something more than we find in scientific instruments. What is this something more? The traditional answer would be: consciousness. But this answer, right or wrong, is not what we are seeking at the moment, because we are considering the percipient as he appears to an outside observer, to whom his “consciousness” is only an inference. Is there anything in perception as viewed from without that distinguishes it from the sensitivity of a scientific instrument? There is, of course, the fact that human beings are sensitive to a greater variety of stimuli than any instrument. Each separate sense-organ can be surpassed by something made artificially sensitive to its particular stimulus. Photographic plates can photograph stars that we cannot see; clinical thermometers register differences of temperature that we cannot feel; and so on. But there is no way of combining a microscope, a microphone, a thermometer, a galvanometer, and so on, into a single organism which will react in an integral manner to the combination of all the different stimuli that affect its different “sense-organs”. This, however, is perhaps only a proof that our mechanical skill is not so great as it may in time become. It is certainly not enough to define the difference between a dead instrument and a living body. The chief difference—perhaps the only one from our present point of view—is that living bodies are subject to the law of association or of the “conditioned reflex”. Consider, for instance, an automatic machine. It has a reflex which makes it sensitive to pennies, in response to which it gives up chocolate. But it never learns to give up chocolate on merely seeing a penny, or hearing the word “penny”. If you kept it in your house, and said “Abracadabra” to it every time you inserted a penny, it would not in the end be moved to action by the mere word “Abracadabra”. Its reflexes remain unconditioned, as do some of ours, such as sneezing. But with us sneezing is peculiar in this respect—hence its unimportance. Most of our reflexes can be conditioned, and the conditioned reflex can in turn be conditioned afresh, and so on without limit. This is what makes the reactions of the higher animals, and especially of man, so much more interesting and complicated than the reactions of machines. Let us see whether this one law will suffice to distinguish perception from other forms of sensitivity. The variability in a human being’s responses to a given stimulus has given rise to the traditional distinction between cognition and volition. When one’s rich uncle comes for a visit, smiles are the natural response; after he has lost his money, a colder demeanour results from the new conditioning. Thus the reaction to the stimulus has come to be divided into two parts, one purely receptive and sensory, the other active and motor. Perception, as traditionally conceived, is, so to speak, the end term of the receptive-sensory part of the reaction, while volition (in its widest sense) is the first term of the active-motor part of the reaction. It was possible to suppose that the receptive part of the reaction would be always the same for the same stimulus, and that the difference due to experience would only arise in the motor part. The last term of the passive part, as it appears to the person concerned, was called “sensation”. But in fact the influence of the law of conditioned reflexes goes much deeper than this theory supposed. As we saw, the contraction of the pupil, which is normally due to bright light, can be conditioned so as to result from a loud noise. What we see depends largely upon muscular adjustments of the eyes, which we make quite unconsciously. But apart from the contraction of the pupil only one of them is a true reflex, namely turning the eyes towards a bright light. This is a movement which children can perform on the day of their birth; I know this, not merely from personal observation, but also, what is more, from the text-books. But new-born infants cannot follow a moving light with their eyes, nor can they focus or accommodate. As a consequence, the purely receptive part of their reaction to visual objects, in so far as this reaction is visual, is different from that of adults or older children, whose eye muscles adjust themselves so as to see clearly. But here again all sorts of factors enter in. Innumerable objects are in our field of vision, but only some (at most) are interesting to us. If some one says “look, there’s a snake”, we adjust our eyes afresh and obtain a new “sensation”. Then, when the purely visual part is finished, there are stimulations, by association, of other centres in the brain. There are pictures, in Köhler’s book, of apes watching other apes on the top of insecure piles of boxes, and the spectators have their arms raised in sympathetic balancing movements. Any one who watches gymnastics or skilful dancing is liable to experience sympathetic muscular contractions. Any visual object that we might be touching will stimulate incipient touch reactions, but the sun, moon, and stars do not. Conversely, visual reactions may be stimulated through association with other stimuli. When motor-cars were still uncommon, I was walking one day with a friend when a tire punctured in our neighbourhood with a loud report. He thought it was a revolver, and averred that he had seen the flash. In dreams, this sort of mechanism operates uncontrolled. Some stimulus—say the noise of the maid knocking at the door—becomes interpreted in fantastic ways which are governed by association. I remember once dreaming that I was in an inn in the country in Germany and was wakened by a choir singing outside my window. Finally I really woke, and found that a spring shower was making a very musical noise on the roof. At least, I heard a very musical noise, and now re-interpreted it as a shower on the roof. This hypothesis I confirmed by looking out of the window. In waking life we are critical of the interpretative hypotheses that occur to us, and therefore do not make such wild mistakes as in dreams. But the creative, as opposed to the critical, mechanism is the same in waking life as it is in dreams: there is always far more richness in the experience than the sensory stimulus alone would warrant. All adaptation to environment acquired during the life of the individual might be regarded as learning to dream dreams that succeed rather than dreams that fail. The dreams we have when we are asleep usually end in a surprise: the dreams we have in waking life are less apt to do so. Sometimes they do, as when pride goes before a fall; but in that case they are regarded as showing maladjustment, unless there is some large external cause, such as an earthquake. One might say that a person properly adapted to his environment is one whose dreams never end in the sort of surprise that would wake him up. In that case, he will think that his dreams are objective reality. But if modern physics is to be believed, the dreams we call waking perceptions have only a very little more resemblance to objective reality than the fantastic dreams of sleep. They have some truth, but only just so much as is required to make them useful. Until we begin to reflect, we unhesitatingly assume that what we see is really “there” in the outside world, except in such cases as reflections in mirrors. Physics and the theory of the way in which perceptions are caused show that this naive belief cannot be quite true. Perception may, and I think does, enable us to know something of the outer world, but it is not the direct revelation that we naturally suppose it to be. We cannot go into this question adequately until we have considered what the philosopher has to learn from physics; I am