animal is reflective, like some men, it comes to think that it had the final situation in mind throughout; sometimes it comes to know what situation will bring satisfaction, so that in fact the discomfort does bring the thought of what will allay it. Nevertheless the sensation involving discomfort remains the prime mover.
This brings us to the question of the nature of discomfort and pleasure. Since Kant it has been customary to recognize three great divisions of mental phenomena, which are typified by knowledge, desire and feeling, where “feeling” is used to mean pleasure and discomfort. Of course, “knowledge” is too definite a word: the states of mind concerned are grouped together as “cognitive,” and are to embrace not only beliefs, but perceptions, doubts, and the understanding of concepts. “Desire,” also, is narrower than what is intended: for example, WILL is to be included in this category, and in fact every thing that involves any kind of striving, or “conation” as it is technically called. I do not myself believe that there is any value in this threefold division of the contents of mind. I believe that sensations (including images) supply all the “stuff” of the mind, and that everything else can be analysed into groups of sensations related in various ways, or characteristics of sensations or of groups of sensations. As regards belief, I shall give grounds for this view in later lectures. As regards desires, I have given some grounds in this lecture. For the present, it is pleasure and discomfort that concern us. There are broadly three theories that might be held in regard to them. We may regard them as separate existing items in those who experience them, or we may regard them as intrinsic qualities of sensations and other mental occurrences, or we may regard them as mere names for the causal characteristics of the occurrences which are uncomfortable or pleasant. The first of these theories, namely, that which regards discomfort and pleasure as actual contents in those who experience them, has, I think, nothing conclusive to be said in its favour.* It is suggested chiefly by an ambiguity in the word “pain,” which has misled many people, including Berkeley, whom it supplied with one of his arguments for subjective idealism. We may use “pain” as the opposite of “pleasure,” and “painful” as the opposite of “pleasant,” or we may use “pain” to mean a certain sort of sensation, on a level with the sensations of heat and cold and touch. The latter use of the word has prevailed in psychological literature, and it is now no longer used as the opposite of “pleasure.” Dr. H. Head, in a recent publication, has stated this distinction as follows:**
* Various arguments in its favour are advanced by A. Wohlgemuth, “On the feelings and their neural correlate, with an examination of the nature of pain,” “British Journal of Psychology,” viii, 4. (1917). But as these arguments are largely a reductio ad absurdum of other theories, among which that which I am advocating is not included, I cannot regard them as establishing their contention.
** “Sensation and the Cerebral Cortex,” “Brain,” vol. xli, part ii (September, 1918), p. 90. Cf. also Wohlgemuth, loc. cit. pp. 437, 450.
“It is necessary at the outset to distinguish clearly between ‘discomfort’ and ‘pain.’ Pain is a distinct sensory quality equivalent to heat and cold, and its intensity can be roughly graded according to the force expended in stimulation. Discomfort, on the other hand, is that feeling-tone which is directly opposed to pleasure. It may accompany sensations not in themselves essentially painful; as for instance that produced by tickling the sole of the foot. The reaction produced by repeated pricking contains both these elements; for it evokes that sensory quality known as pain, accompanied by a disagreeable feeling-tone, which we have called discomfort. On the other hand, excessive pressure, except when applied directly over some nerve-trunk, tends to excite more discomfort than pain.”
The confusion between discomfort and pain has made people regard discomfort as a more substantial thing than it is, and this in turn has reacted upon the view taken of pleasure, since discomfort and pleasure are evidently on a level in this respect. As soon as discomfort is clearly distinguished from the sensation of pain, it becomes more natural to regard discomfort and pleasure as properties of mental occurrences than to regard them as separate mental occurrences on their own account. I shall therefore dismiss the view that they are separate mental occurrences, and regard them as properties of such experiences as would be called respectively uncomfortable and pleasant.
It remains to be examined whether they are actual qualities of such occurrences, or are merely differences as to causal properties. I do not myself see any way of deciding this question; either view seems equally capable of accounting for the facts. If this is true, it is safer to avoid the assumption that there are such intrinsic qualities of mental occurrences as are in question, and to assume only the causal differences which are undeniable. Without condemning the intrinsic theory, we can define discomfort and pleasure as consisting in causal properties, and say only what will hold on either of the two theories. Following this course, we shall say:
“Discomfort” is a property of a sensation or other mental occurrence, consisting in the fact that the occurrence in question stimulates voluntary or reflex movements tending to produce some more or less definite change involving the cessation of the occurrence.
“Pleasure” is a property of a sensation or other mental occurrence, consisting in the fact that the occurrence in question either does not stimulate any voluntary or reflex movement, or, if it does, stimulates only such as tend to prolong the occurrence in question.*
* Cf. Thorndike, op. cit., p. 243.
“Conscious” desire, which we have now to consider, consists of desire in the sense hitherto discussed, together with a true belief as to its “purpose,” i.e. as to the state of affairs that will bring quiescence with cessation of the discomfort. If our theory of desire is correct, a belief as to its purpose may very well be erroneous, since only experience can show what causes a discomfort to cease. When the experience needed is common and simple, as in the case of hunger, a mistake is not very probable. But in other cases–e.g. erotic desire in those who have had little or no experience of its satisfaction–mistakes are to be expected, and do in fact very often occur. The practice of inhibiting impulses, which is to a great extent necessary to civilized life, makes mistakes easier, by preventing experience of the actions to which a desire would otherwise lead, and by often causing the inhibited impulses themselves to be unnoticed or quickly forgotten. The perfectly natural mistakes which thus arise constitute a large proportion of what is, mistakenly in part, called self-deception, and attributed by Freud to the “censor.”
But there is a further point which needs emphasizing, namely, that a belief that something is desired has often a tendency to cause the very desire that is believed in. It is this fact that makes the effect of “consciousness” on desire so complicated.
When we believe that we desire a certain state of affairs, that often tends to cause a real desire for it. This is due partly to the influence of words upon our emotions, in rhetoric for example, and partly to the general fact that discomfort normally belongs to the belief that we desire such-and-such a thing that we do not possess. Thus what was originally a false opinion as to the object of a desire acquires a certain truth: the false opinion generates a secondary subsidiary desire, which nevertheless becomes real. Let us take an illustration. Suppose you have been jilted in a way which wounds your vanity. Your natural impulsive desire will be of the sort expressed in Donne’s poem:
When by thy scorn, O Murderess, I am dead,
in which he explains how he will haunt the poor lady as a ghost, and prevent her from enjoying a moment’s peace. But two things stand in the way of your expressing yourself so naturally: on the one hand, your vanity, which will not acknowledge how hard you are hit; on the other hand, your conviction that you are a civilized and humane person, who could not possibly indulge so crude a desire as revenge. You will therefore experience a restlessness which will at first seem quite aimless, but will finally resolve itself in a conscious desire to change your profession, or go round the world, or conceal your identity and live in Putney, like Arnold Bennett’s hero. Although the prime cause of this desire is a false judgment as to your previous unconscious desire, yet the new conscious desire has its own derivative genuineness, and may influence your actions to the extent of sending you round the world. The initial mistake, however, will have effects of two kinds. First, in uncontrolled moments, under the influence of sleepiness or drink or delirium, you will say things calculated to injure the faithless deceiver. Secondly, you will find travel disappointing, and the East less fascinating than you had hoped–unless, some day, you hear that the wicked one has in turn been jilted. If this happens, you will believe that you feel sincere sympathy, but you will suddenly be much more delighted than before with the beauties of tropical islands or the wonders of Chinese art. A secondary desire, derived from a false judgment as to a primary desire, has its own power of influencing action, and is therefore a real desire according to our definition. But it has not the same power as a primary desire of bringing thorough satisfaction when it is realized; so long as the primary desire remains unsatisfied, restlessness continues in spite of the secondary desire’s success. Hence arises a belief in the vanity of human wishes: the vain wishes are those that are secondary, but mistaken beliefs prevent us from realizing that they are secondary.
What may, with some propriety, be called self-deception arises through the operation of desires for beliefs. We desire many things which it is not in our power to achieve: that we should be universally popular and admired, that our work should be the wonder of the age, and that the universe should be so ordered as to bring ultimate happiness to all, though not to our enemies until they have repented and been purified by suffering. Such desires are too large to be achieved through our own efforts. But it is found that a considerable portion of the satisfaction which these things would bring us if they were realized is to be achieved by the much easier operation of believing that they are or will be realized. This desire for beliefs, as opposed to desire for the actual facts, is a particular case of secondary desire, and, like all secondary desire its satisfaction does not lead to a complete cessation of the initial discomfort. Nevertheless, desire for beliefs, as opposed to desire for facts, is exceedingly potent both individually and socially. According to the form of belief desired, it is called vanity, optimism, or religion. Those who have sufficient power usually imprison or put to death any one who tries to shake their faith in their own excellence or in that of the universe; it is for this reason that seditious libel and blasphemy have always been, and still are, criminal offences.
It is very largely through desires for beliefs that the primitive nature of desire has become so hidden, and that the part played by consciousness has been so confusing and so exaggerated.
We may now summarize our analysis of desire and feeling.
A mental occurrence of any kind–sensation, image, belief, or emotion–may be a cause of a series of actions, continuing, unless interrupted, until some more or less definite state of affairs is realized. Such a series of actions we call a “behaviour-cycle.” The degree of definiteness may vary greatly: hunger requires only food in general, whereas the sight of a particular piece of food raises a desire which requires the eating of that piece of food. The property of causing such a cycle of occurrences is called “discomfort”; the property of the mental occurrences in which the cycle ends is called ” pleasure.” The actions constituting the cycle must not be purely mechanical, i.e. they must be bodily movements in whose causation the special properties of nervous tissue are involved. The cycle ends in a condition of quiescence, or of such action as tends only to preserve the status quo. The state of affairs in which this condition of quiescence is achieved is called the “purpose” of the cycle, and the initial mental occurrence involving discomfort is called a “desire” for the state of affairs that brings quiescence. A desire is called “conscious” when it is accompanied by a true belief as to the state of affairs that will bring quiescence; otherwise it is called “unconscious.” All primitive desire is unconscious, and in human beings beliefs as to the purposes of desires are often mistaken. These mistaken beliefs generate secondary desires, which cause various interesting complications in the psychology of human desire, without fundamentally altering the character which it shares with animal desire.
LECTURE IV. INFLUENCE OF PAST HISTORY ON PRESENT OCCURRENCES IN LIVING ORGANISMS
In this lecture we shall be concerned with a very general characteristic which broadly, though not absolutely, distinguishes the behaviour of living organisms from that of dead matter. The characteristic in question is this:
The response of an organism to a given stimulus is very often dependent upon the past history of the organism, and not merely upon the stimulus and the HITHERTO DISCOVERABLE present state of the organism.
This characteristic is embodied in the saying “a burnt child fears the fire.” The burn may have left no visible traces, yet it modifies the reaction of the child in the presence of fire. It is customary to assume that, in such cases, the past operates by modifying the structure of the brain, not directly. I have no wish to suggest that this hypothesis is false; I wish only to point out that it is a hypothesis. At the end of the present lecture I shall examine the grounds in its favour. If we confine ourselves to facts which have been actually observed, we must say that past occurrences, in addition to the present stimulus and the present ascertainable condition of the organism, enter into the causation of the response.
The characteristic is not wholly confined to living organisms. For example, magnetized steel looks just like steel which has not been magnetized, but its behaviour is in some ways different. In the case of dead matter, however, such phenomena are less frequent and important than in the case of living organisms, and it is far less difficult to invent satisfactory hypotheses as to the microscopic changes of structure which mediate between the past occurrence and the present changed response. In the case of living organisms, practically everything that is distinctive both of their physical and of their mental behaviour is bound up with this persistent influence of the past. Further, speaking broadly, the change in response is usually of a kind that is biologically advantageous to the organism.
Following a suggestion derived from Semon (“Die Mneme,” Leipzig, 1904; 2nd edition, 1908, English translation, Allen & Unwin, 1921; “Die mnemischen Empfindungen,” Leipzig, l909), we will give the name of “mnemic phenomena” to those responses of an organism which, so far as hitherto observed facts are concerned, can only be brought under causal laws by including past occurrences in the history of the organism as part of the causes of the present response. I do not mean merely–what would always be the case–that past occurrences are part of a CHAIN of causes leading to the present event. I mean that, in attempting to state the PROXIMATE cause of the present event, some past event or events must be included, unless we take refuge in hypothetical modifications of brain structure.) For example: you smell peat-smoke, and you recall some occasion when you smelt it before. The cause of your recollection, so far as hitherto observ able phenomena are concerned, consists both of the peat smoke (present stimulus) and of the former occasion (past experience). The same stimulus will not produce the same recollection in another man who did not share your former experience, although the former experience left no OBSERVABLE traces in the structure of the brain. According to the maxim “same cause, same effect,” we cannot therefore regard the peat-smoke alone as the cause of your recollection, since it does not have the same effect in other cases. The cause of your recollection must be both the peat-smoke and the past occurrence. Accordingly your recollection is an instance of what we are calling “mnemic phenomena.”
Before going further, it will be well to give illustrations of different classes of mnemic phenomena.
(a) ACQUIRED HABITS.–In Lecture II we saw how animals can learn by experience how to get out of cages or mazes, or perform other actions which are useful to them but not provided for by their instincts alone. A cat which is put into a cage of which it has had experience behaves differently from the way in which it behaved at first. We can easily invent hypotheses, which are quite likely to be true, as to connections in the brain caused by past experience, and themselves causing the different response. But the observable fact is that the stimulus of being in the cage produces differing results with repetition, and that the ascertainable cause of the cat’s behaviour is not merely the cage and its own ascertainable organization, but also its past history in regard to the cage. From our present point of view, the matter is independent of the question whether the cat’s behaviour is due to some mental fact called “knowledge,” or displays a merely bodily habit. Our habitual knowledge is not always in our minds, but is called up by the appropriate stimuli. If we are asked “What is the capital of France?” we answer “Paris,” because of past experience; the past experience is as essential as the present question in the causation of our response. Thus all our habitual knowledge consists of acquired habits, and comes under the head of mnemic phenomena.
(b) IMAGES.–I shall have much to say about images in a later lecture; for the present I am merely concerned with them in so far as they are “copies” of past sensations. When you hear New York spoken of, some image probably comes into your mind, either of the place itself (if you have been there), or of some picture of it (if you have not). The image is due to your past experience, as well as to the present stimulus of the words “New York.” Similarly, the images you have in dreams are all dependent upon your past experience, as well as upon the present stimulus to dreaming. It is generally believed that all images, in their simpler parts, are copies of sensations; if so, their mnemic character is evident. This is important, not only on its own account, but also because, as we shall see later, images play an essential part in what is called “thinking.”
(c) ASSOCIATION.–The broad fact of association, on the mental side, is that when we experience something which we have experienced before, it tends to call up the context of the former experience. The smell of peat-smoke recalling a former scene is an instance which we discussed a moment ago. This is obviously a mnemic phenomenon. There is also a more purely physical association, which is indistinguishable from physical habit. This is the kind studied by Mr. Thorndike in animals, where a certain stimulus is associated with a certain act. This is the sort which is taught to soldiers in drilling, for example. In such a case there need not be anything mental, but merely a habit of the body. There is no essential distinction between association and habit, and the observations which we made concerning habit as a mnemic phenomenon are equally applicable to association.
(d) NON-SENSATIONAL ELEMENTS IN PERCEPTION.–When we perceive any object of a familiar kind, much of what appears subjectively to be immediately given is really derived from past experience. When we see an object, say a penny, we seem to be aware of its “real” shape we have the impression of something circular, not of something elliptical. In learning to draw, it is necessary to acquire the art of representing things according to the sensation, not according to the perception. And the visual appearance is filled out with feeling of what the object would be like to touch, and so on. This filling out and supplying of the “real” shape and so on consists of the most usual correlates of the sensational core in our perception. It may happen that, in the particular case, the real correlates are unusual; for example, if what we are seeing is a carpet made to look like tiles. If so, the non-sensational part of our perception will be illusory, i.e. it will supply qualities which the object in question does not in fact have. But as a rule objects do have the qualities added by perception, which is to be expected, since experience of what is usual is the cause of the addition. If our experience had been different, we should not fill out sensation in the same way, except in so far as the filling out is instinctive, not acquired. It would seem that, in man, all that makes up space perception, including the correlation of sight and touch and so on, is almost entirely acquired. In that case there is a large mnemic element in all the common perceptions by means of which we handle common objects. And, to take another kind of instance, imagine what our astonishment would be if we were to hear a cat bark or a dog mew. This emotion would be dependent upon past experience, and would therefore be a mnemic phenomenon according to the definition.
(e) MEMORY AS KNOWLEDGE.–The kind of memory of which I am now speaking is definite knowledge of some past event in one’s own experience. From time to time we remember things that have happened to us, because something in the present reminds us of them. Exactly the same present fact would not call up the same memory if our past experience had been different. Thus our remembering is caused by–
(1) The present stimulus,
(2) The past occurrence.
It is therefore a mnemic phenomenon according to our definition. A definition of “mnemic phenomena” which did not include memory would, of course, be a bad one. The point of the definition is not that it includes memory, but that it includes it as one of a class of phenomena which embrace all that is characteristic in the subject matter of psychology.
(f) EXPERIENCE.–The word “experience” is often used very vaguely. James, as we saw, uses it to cover the whole primal stuff of the world, but this usage seems objection able, since, in a purely physical world, things would happen without there being any experience. It is only mnemic phenomena that embody experience. We may say that an animal “experiences” an occurrence when this occurrence modifies the animal’s subsequent behaviour, i.e. when it is the mnemic portion of the cause of future occurrences in the animal’s life. The burnt child that fears the fire has “experienced” the fire, whereas a stick that has been thrown on and taken off again has not “experienced” anything, since it offers no more resistance than before to being thrown on. The essence of “experience” is the modification of behaviour produced by what is experienced. We might, in fact, define one chain of experience, or one biography, as a series of occurrences linked by mnemic causation. I think it is this characteristic, more than any other, that distinguishes sciences dealing with living organisms from physics.
The best writer on mnemic phenomena known to me is Richard Semon, the fundamental part of whose theory I shall endeavour to summarize before going further:
When an organism, either animal or plant, is subjected to a stimulus, producing in it some state of excitement, the removal of the stimulus allows it to return to a condition of equilibrium. But the new state of equilibrium is different from the old, as may be seen by the changed capacity for reaction. The state of equilibrium before the stimulus may be called the “primary indifference-state”; that after the cessation of the stimulus, the “secondary indifference-state.” We define the “engraphic effect” of a stimulus as the effect in making a difference between the primary and secondary indifference-states, and this difference itself we define as the “engram” due to the stimulus. “Mnemic phenomena” are defined as those due to engrams; in animals, they are specially associated with the nervous system, but not exclusively, even in man.
When two stimuli occur together, one of them, occurring afterwards, may call out the reaction for the other also. We call this an “ekphoric influence,” and stimuli having this character are called “ekphoric stimuli.” In such a case we call the engrams of the two stimuli “associated.” All simultaneously generated engrams are associated; there is also association of successively aroused engrams, though this is reducible to simultaneous association. In fact, it is not an isolated stimulus that leaves an engram, but the totality of the stimuli at any moment; consequently any portion of this totality tends, if it recurs, to arouse the whole reaction which was aroused before. Semon holds that engrams can be inherited, and that an animal’s innate habits may be due to the experience of its ancestors; on this subject he refers to Samuel Butler.
Semon formulates two “mnemic principles.” The first, or “Law of Engraphy,” is as follows: “All simultaneous excitements in an organism form a connected simultaneous excitement-complex, which as such works engraphically, i.e. leaves behind a connected engram-complex, which in so far forms a whole” (“Die mnemischen Empfindungen,” p. 146). The second mnemic principle, or “Law of Ekphory,” is as follows: “The partial return of the energetic situation which formerly worked engraphically operates ekphorically on a simultaneous engram-complex” (ib., p. 173). These two laws together represent in part a hypothesis (the engram), and in part an observable fact. The observable fact is that, when a certain complex of stimuli has originally caused a certain complex of reactions, the recurrence of part of the stimuli tends to cause the recurrence of the whole of the reactions.
Semon’s applications of his fundamental ideas in various directions are interesting and ingenious. Some of them will concern us later, but for the present it is the fundamental character of mnemic phenomena that is in question.
Concerning the nature of an engram, Semon confesses that at present it is impossible to say more than that it must consist in some material alteration in the body of the organism (“Die mnemischen Empfindungen,” p. 376). It is, in fact, hypothetical, invoked for theoretical uses, and not an outcome of direct observation. No doubt physiology, especially the disturbances of memory through lesions in the brain, affords grounds for this hypothesis; nevertheless it does remain a hypothesis, the validity of which will be discussed at the end of this lecture.
I am inclined to think that, in the present state of physiology, the introduction of the engram does not serve to simplify the account of mnemic phenomena. We can, I think, formulate the known laws of such phenomena in terms, wholly, of observable facts, by recognizing provisionally what we may call “mnemic causation.” By this I mean that kind of causation of which I spoke at the beginning of this lecture, that kind, namely, in which the proximate cause consists not merely of a present event, but of this together with a past event. I do not wish to urge that this form of causation is ultimate, but that, in the present state of our knowledge, it affords a simplification, and enables us to state laws of behaviour in less hypothetical terms than we should otherwise have to employ.
The clearest instance of what I mean is recollection of a past event. What we observe is that certain present stimuli lead us to recollect certain occurrences, but that at times when we are not recollecting them, there is nothing discoverable in our minds that could be called memory of them. Memories, as mental facts, arise from time to time, but do not, so far as we can see, exist in any shape while they are “latent.” In fact, when we say that they are “latent,” we mean merely that they will exist under certain circumstances. If, then, there is to be some standing difference between the person who can remember a certain fact and the person who cannot, that standing difference must be, not in anything mental, but in the brain. It is quite probable that there is such a difference in the brain, but its nature is unknown and it remains hypothetical. Everything that has, so far, been made matter of observation as regards this question can be put together in the statement: When a certain complex of sensations has occurred to a man, the recurrence of part of the complex tends to arouse the recollection of the whole. In like manner, we can collect all mnemic phenomena in living organisms under a single law, which contains what is hitherto verifiable in Semon’s two laws. This single law is:
IF A COMPLEX STIMULUS A HAS CAUSED A COMPLEX REACTION B IN AN ORGANISM, THE OCCURRENCE OF A PART OF A ON A FUTURE OCCASION TENDS TO CAUSE THE WHOLE REACTION B.
This law would need to be supplemented by some account of the influence of frequency, and so on; but it seems to contain the essential characteristic of mnemic phenomena, without admixture of anything hypothetical.
Whenever the effect resulting from a stimulus to an organism differs according to the past history of the organism, without our being able actually to detect any relevant difference in its present structure, we will speak of “mnemic causation,” provided we can discover laws embodying the influence of the past. In ordinary physical causation, as it appears to common sense, we have approximate uniformities of sequence, such as “lightning is followed by thunder,” “drunkenness is followed by headache,” and so on. None of these sequences are theoretically invariable, since something may intervene to disturb them. In order to obtain invariable physical laws, we have to proceed to differential equations, showing the direction of change at each moment, not the integral change after a finite interval, however short. But for the purposes of daily life many sequences are to all in tents and purposes invariable. With the behaviour of human beings, however, this is by no means the case. If you say to an Englishman, “You have a smut on your nose,” he will proceed to remove it, but there will be no such effect if you say the same thing to a Frenchman who knows no English. The effect of words upon the hearer is a mnemic phenomena, since it depends upon the past experience which gave him understanding of the words. If there are to be purely psychological causal laws, taking no account of the brain and the rest of the body, they will have to be of the form, not “X now causes Y now,” but–
“A, B, C, . . . in the past, together with X now, cause Y now.” For it cannot be successfully maintained that our understanding of a word, for example, is an actual existent content of the mind at times when we are not thinking of the word. It is merely what may be called a “disposition,” i.e. it is capable of being aroused whenever we hear the word or happen to think of it. A “disposition” is not something actual, but merely the mnemic portion of a mnemic causal law.
In such a law as “A, B, C, . . . in the past, together with X now, cause Y now,” we will call A, B, C, . . . the mnemic cause, X the occasion or stimulus, and Y the reaction. All cases in which experience influences behaviour are instances of mnemic causation.
Believers in psycho-physical parallelism hold that psychology can theoretically be freed entirely from all dependence on physiology or physics. That is to say, they believe that every psychical event has a psychical cause and a physical concomitant. If there is to be parallelism, it is easy to prove by mathematical logic that the causation in physical and psychical matters must be of the same sort, and it is impossible that mnemic causation should exist in psychology but not in physics. But if psychology is to be independent of physiology, and if physiology can be reduced to physics, it would seem that mnemic causation is essential in psychology. Otherwise we shall be compelled to believe that all our knowledge, all our store of images and memories, all our mental habits, are at all times existing in some latent mental form, and are not merely aroused by the stimuli which lead to their display. This is a very difficult hypothesis. It seems to me that if, as a matter of method rather than metaphysics, we desire to obtain as much independence for psychology as is practically feasible, we shall do better to accept mnemic causation in psychology protem, and therefore reject parallelism, since there is no good ground for admitting mnemic causation in physics.
It is perhaps worth while to observe that mnemic causation is what led Bergson to deny that there is causation. at all in the psychical sphere. He points out, very truly, that the same stimulus, repeated, does not have the same consequences, and he argues that this is contrary to the maxim, “same cause, same effect.” It is only necessary, however, to take account of past occurrences and include them with the cause, in order to re-establish the maxim, and the possibility of psychological causal laws. The metaphysical conception of a cause lingers in our manner of viewing causal laws: we want to be able to FEEL a connection between cause and effect, and to be able to imagine the cause as “operating.” This makes us unwilling to regard causal laws as MERELY observed uniformities of sequence; yet that is all that science has to offer. To ask why such-and-such a kind of sequence occurs is either to ask a meaningless question, or to demand some more general kind of sequence which includes the one in question. The widest empirical laws of sequence known at any time can only be “explained” in the sense of being subsumed by later discoveries under wider laws; but these wider laws, until they in turn are subsumed, will remain brute facts, resting solely upon observation, not upon some supposed inherent rationality.
There is therefore no a priori objection to a causal law in which part of the cause has ceased to exist. To argue against such a law on the ground that what is past cannot operate now, is to introduce the old metaphysical notion of cause, for which science can find no place. The only reason that could be validly alleged against mnemic causation would be that, in fact, all the phenomena can be explained without it. They are explained without it by Semon’s “engram,” or by any theory which regards the results of experience as embodied in modifications of the brain and nerves. But they are not explained, unless with extreme artificiality, by any theory which regards the latent effects of experience as psychical rather than physical. Those who desire to make psychology as far as possible independent of physiology would do well, it seems to me, if they adopted mnemic causation. For my part, however, I have no such desire, and I shall therefore endeavour to state the grounds which occur to me in favour of some such view as that of the “engram.”
One of the first points to be urged is that mnemic phenomena are just as much to be found in physiology as in psychology. They are even to be found in plants, as Sir Francis Darwin pointed out (cf. Semon, “Die Mneme,” 2nd edition, p. 28 n.). Habit is a characteristic of the body at least as much as of the mind. We should, therefore, be compelled to allow the intrusion of mnemic causation, if admitted at all, into non-psychological regions, which ought, one feels, to be subject only to causation of the ordinary physical sort. The fact is that a great deal of what, at first sight, distinguishes psychology from physics is found, on examination, to be common to psychology and physiology; this whole question of the influence of experience is a case in point. Now it is possible, of course, to take the view advocated by Professor J. S. Haldane, who contends that physiology is not theoretically reducible to physics and chemistry.* But the weight of opinion among physiologists appears to be against him on this point; and we ought certainly to require very strong evidence before admitting any such breach of continuity as between living and dead matter. The argument from the existence of mnemic phenomena in physiology must therefore be allowed a certain weight against the hypothesis that mnemic causation is ultimate.
* See his “The New Physiology and Other Addresses,” Griffin, 1919, also the symposium, “Are Physical, Biological and Psychological Categories Irreducible?” in “Life and Finite Individuality,” edited for the Aristotelian Society, with an Introduction. By H. Wildon Carr, Williams & Norgate, 1918.
The argument from the connection of brain-lesions with loss of memory is not so strong as it looks, though it has also, some weight. What we know is that memory, and mnemic phenomena generally, can be disturbed or destroyed by changes in the brain. This certainly proves that the brain plays an essential part in the causation of memory, but does not prove that a certain state of the brain is, by itself, a sufficient condition for the existence of memory. Yet it is this last that has to be proved. The theory of the engram, or any similar theory, has to maintain that, given a body and brain in a suitable state, a man will have a certain memory, without the need of any further conditions. What is known, however, is only that he will not have memories if his body and brain are not in a suitable state. That is to say, the appropriate state of body and brain is proved to be necessary for memory, but not to be sufficient. So far, therefore, as our definite knowledge goes, memory may require for its causation a past occurrence as well as a certain present state of the brain.
In order to prove conclusively that mnemic phenomena arise whenever certain physiological conditions are fulfilled, we ought to be able actually to see differences between the brain of a man who speaks English and that of a man who speaks French, between the brain of a man who has seen New York and can recall it, and that of a man who has never seen that city. It may be that the time will come when this will be possible, but at present we are very far removed from it. At present, there is, so far as I am aware, no good evidence that every difference between the knowledge possessed by A and that possessed by B is paralleled by some difference in their brains. We may believe that this is the case, but if we do, our belief is based upon analogies and general scientific maxims, not upon any foundation of detailed observation. I am myself inclined, as a working hypothesis, to adopt the belief in question, and to hold that past experience only affects present behaviour through modifications of physiological structure. But the evidence seems not quite conclusive, so that I do not think we ought to forget the other hypothesis, or to reject entirely the possibility that mnemic causation may be the ultimate explanation of mnemic phenomena. I say this, not because I think it LIKELY that mnemic causation is ultimate, but merely because I think it POSSIBLE, and because it often turns out important to the progress of science to remember hypotheses which have previously seemed improbable.
LECTURE V. PSYCHOLOGICAL AND PHYSICAL CAUSAL LAWS
The traditional conception of cause and effect is one which modern science shows to be fundamentally erroneous, and requiring to be replaced by a quite different notion, that of LAWS OF CHANGE. In the traditional conception, a particular event A caused a particular event B, and by this it was implied that, given any event B, some earlier event A could be discovered which had a relation to it, such that–
(1) Whenever A occurred, it was followed by B;
(2) In this sequence, there was something “necessary,” not a mere de facto occurrence of A first and then B.
The second point is illustrated by the old discussion as to whether it can be said that day causes night, on the ground that day is always followed by night. The orthodox answer was that day could not be called the cause of night, because it would not be followed by night if the earth’s rotation were to cease, or rather to grow so slow that one complete rotation would take a year. A cause, it was held, must be such that under no conceivable circumstances could it fail to be followed by its effect.
As a matter of fact, such sequences as were sought by believers in the traditional form of causation have not so far been found in nature. Everything in nature is apparently in a state of continuous change,* so that what we call one “event” turns out to be really a process. If this event is to cause another event, the two will have to be contiguous in time; for if there is any interval between them, something may happen during that interval to prevent the expected effect. Cause and effect, therefore, will have to be temporally contiguous processes. It is difficult to believe, at any rate where physical laws are concerned, that the earlier part of the process which is the cause can make any difference to the effect, so long as the later part of the process which is the cause remains unchanged. Suppose, for example, that a man dies of arsenic poisoning, we say that his taking arsenic was the cause of death. But clearly the process by which he acquired the arsenic is irrelevant: everything that happened before he swallowed it may be ignored, since it cannot alter the effect except in so far as it alters his condition at the moment of taking the dose. But we may go further: swallowing arsenic is not really the proximate cause of death, since a man might be shot through the head immediately after taking the dose, and then it would not be of arsenic that he would die. The arsenic produces certain physiological changes, which take a finite time before they end in death. The earlier parts of these changes can be ruled out in the same way as we can rule out the process by which the arsenic was acquired. Proceeding in this way, we can shorten the process which we are calling the cause more and more. Similarly we shall have to shorten the effect. It may happen that immediately after the man’s death his body is blown to pieces by a bomb. We cannot say what will happen after the man’s death, through merely knowing that he has died as the result of arsenic poisoning. Thus, if we are to take the cause as one event and the effect as another, both must be shortened indefinitely. The result is that we merely have, as the embodiment of our causal law, a certain direction of change at each moment. Hence we are brought to differential equations as embodying causal laws. A physical law does not say “A will be followed by B,” but tells us what acceleration a particle will have under given circumstances, i.e. it tells us how the particle’s motion is changing at each moment, not where the particle will be at some future moment.
* The theory of quanta suggests that the continuity is only apparent. If so, we shall be able theoretically to reach events which are not processes. But in what is directly observable there is still apparent continuity, which justifies the above remarks for the prevent.
Laws embodied in differential equations may possibly be exact, but cannot be known to be so. All that we can know empirically is approximate and liable to exceptions; the exact laws that are assumed in physics are known to be somewhere near the truth, but are not known to be true just as they stand. The laws that we actually know empirically have the form of the traditional causal laws, except that they are not to be regarded as universal or necessary. “Taking arsenic is followed by death” is a good empirical generalization; it may have exceptions, but they will be rare. As against the professedly exact laws of physics, such empirical generalizations have the advantage that they deal with observable phenomena. We cannot observe infinitesimals, whether in time or space; we do not even know whether time and space are infinitely divisible. Therefore rough empirical generalizations have a definite place in science, in spite of not being exact of universal. They are the data for more exact laws, and the grounds for believing that they are USUALLY true are stronger than the grounds for believing that the more exact laws are ALWAYS true.
Science starts, therefore, from generalizations of the form, “A is usually followed by B.” This is the nearest approach that can be made to a causal law of the traditional sort. It may happen in any particular instance that A is ALWAYS followed by B, but we cannot know this, since we cannot foresee all the perfectly possible circumstances that might make the sequence fail, or know that none of them will actually occur. If, however, we know of a very large number of cases in which A is followed by B, and few or none in which the sequence fails, we shall in PRACTICE be justified in saying “A causes B,” provided we do not attach to the notion of cause any of the metaphysical superstitions that have gathered about the word.
There is another point, besides lack of universality and necessity, which it is important to realize as regards causes in the above sense, and that is the lack of uniqueness. It is generally assumed that, given any event, there is some one phenomenon which is THE cause of the event in question. This seems to be a mere mistake. Cause, in the only sense in which it can be practically applied, means “nearly invariable antecedent.” We cannot in practice obtain an antecedent which is QUITE invariable, for this would require us to take account of the whole universe, since something not taken account of may prevent the expected effect. We cannot distinguish, among nearly invariable antecedents, one as THE cause, and the others as merely its concomitants: the attempt to do this depends upon a notion of cause which is derived from will, and will (as we shall see later) is not at all the sort of thing that it is generally supposed to be, nor is there any reason to think that in the physical world there is anything even remotely analogous to what will is supposed to be. If we could find one antecedent, and only one, that was QUITE invariable, we could call that one THE cause without introducing any notion derived from mistaken ideas about will. But in fact we cannot find any antecedent that we know to be quite invariable, and we can find many that are nearly so. For example, men leave a factory for dinner when the hooter sounds at twelve o’clock. You may say the hooter is THE cause of their leaving. But innumerable other hooters in other factories, which also always sound at twelve o’clock, have just as good a right to be called the cause. Thus every event has many nearly invariable antecedents, and therefore many antecedents which may be called its cause.
The laws of traditional physics, in the form in which they deal with movements of matter or electricity, have an apparent simplicity which somewhat conceals the empirical character of what they assert. A piece of matter, as it is known empirically, is not a single existing thing, but a system of existing things. When several people simultaneously see the same table, they all see something different; therefore “the” table, which they are supposed all to see, must be either a hypothesis or a construction. “The” table is to be neutral as between different observers: it does not favour the aspect seen by one man at the expense of that seen by another. It was natural, though to my mind mistaken, to regard the “real” table as the common cause of all the appearances which the table presents (as we say) to different observers. But why should we suppose that there is some one common cause of all these appearances? As we have just seen, the notion of “cause” is not so reliable as to allow us to infer the existence of something that, by its very nature, can never be observed.
Instead of looking for an impartial source, we can secure neutrality by the equal representation of all parties. Instead of supposing that there is some unknown cause, the “real” table, behind the different sensations of those who are said to be looking at the table, we may take the whole set of these sensations (together possibly with certain other particulars) as actually BEING the table. That is to say, the table which is neutral as between different observers (actual and possible) is the set of all those particulars which would naturally be called “aspects” of the table from different points of view. (This is a first approximation, modified later.)
It may be said: If there is no single existent which is the source of all these “aspects,” how are they collected together? The answer is simple: Just as they would be if there were such a single existent. The supposed “real” table underlying its appearances is, in any case, not itself perceived, but inferred, and the question whether such-and-such a particular is an “aspect” of this table is only to be settled by the connection of the particular in question with the one or more particulars by which the table is defined. That is to say, even if we assume a “real” table, the particulars which are its aspects have to be collected together by their relations to each other, not to it, since it is merely inferred from them. We have only, therefore, to notice how they are collected together, and we can then keep the collection without assuming any “real” table as distinct from the collection. When different people see what they call the same table, they see things which are not exactly the same, owing to difference of point of view, but which are sufficiently alike to be described in the same words, so long as no great accuracy or minuteness is sought. These closely similar particulars are collected together by their similarity primarily and, more correctly, by the fact that they are related to each other approximately according to the laws of perspective and of reflection and diffraction of light. I suggest, as a first approximation, that these particulars, together with such correlated others as are unperceived, jointly ARE the table; and that a similar definition applies to all physical objects.*
*See “Our Knowledge of the External World” (Allen & Unwin), chaps. iii and iv.
In order to eliminate the reference to our perceptions, which introduces an irrelevant psychological suggestion, I will take a different illustration, namely, stellar photography. A photographic plate exposed on a clear night reproduces the appearance of the portion of the sky concerned, with more or fewer stars according to the power of the telescope that is being used. Each separate star which is photographed produces its separate effect on the plate, just as it would upon ourselves if we were looking at the sky. If we assume, as science normally does, the continuity of physical processes, we are forced to conclude that, at the place where the plate is, and at all places between it and a star which it photographs, SOMETHING is happening which is specially connected with that star. In the days when the aether was less in doubt, we should have said that what was happening was a certain kind of transverse vibration in the aether. But it is not necessary or desirable to be so explicit: all that we need say is that SOMETHING happens which is specially connected with the star in question. It must be something specially connected with that star, since that star produces its own special effect upon the plate. Whatever it is must be the end of a process which starts from the star and radiates outwards, partly on general grounds of continuity, partly to account for the fact that light is transmitted with a certain definite velocity. We thus arrive at the conclusion that, if a certain star is visible at a certain place, or could be photographed by a sufficiently sensitive plate at that place, something is happening there which is specially connected with that star. Therefore in every place at all times a vast multitude of things must be happening, namely, at least one for every physical object which can be seen or photographed from that place. We can classify such happenings on either of two principles:
(1) We can collect together all the happenings in one place, as is done by photography so far as light is concerned;
(2) We can collect together all the happenings, in different places, which are connected in the way that common sense regards as being due to their emanating from one object.
Thus, to return to the stars, we can collect together either–
(1) All the appearances of different stars in a given place, or,
(2) All the appearances of a given star in different places.
But when I speak of “appearances,” I do so only for brevity: I do not mean anything that must “appear” to somebody, but only that happening, whatever it may be, which is connected, at the place in question, with a given physical object–according to the old orthodox theory, it would be a transverse vibration in the aether. Like the different appearances of the table to a number of simultaneous observers, the different particulars that belong to one physical object are to be collected together by continuity and inherent laws of correlation, not by their supposed causal connection with an unknown assumed existent called a piece of matter, which would be a mere unnecessary metaphysical thing in itself. A piece of matter, according to the definition that I propose, is, as a first approximation,* the collection of all those correlated particulars which would normally be regarded as its appearances or effects in different places. Some further elaborations are desirable, but we can ignore them for the present. I shall return to them at the end of this lecture.
*The exact definition of a piece of matter as a construction will be given later.
According to the view that I am suggesting, a physical object or piece of matter is the collection of all those correlated particulars which would be regarded by common sense as its effects or appearances in different places. On the other hand, all the happenings in a given place represent what common sense would regard as the appearances of a number of different objects as viewed from that place. All the happenings in one place may be regarded as the view of the world from that place. I shall call the view of the world from a given place a “perspective.” A photograph represents a perspective. On the other hand, if photographs of the stars were taken in all points throughout space, and in all such photographs a certain star, say Sirius, were picked out whenever it appeared, all the different appearances of Sirius, taken together, would represent Sirius. For the understanding of the difference between psychology and physics it is vital to understand these two ways of classifying particulars, namely:
(1) According to the place where they occur;
(2) According to the system of correlated particulars in different places to which they belong, such system being defined as a physical object.
Given a system of particulars which is a physical object, I shall define that one of the system which is in a given place (if any) as the “appearance of that object in that place.”
When the appearance of an object in a given place changes, it is found that one or other of two things occurs. The two possibilities may be illustrated by an example. You are in a room with a man, whom you see: you may cease to see him either by shutting your eyes or by his going out of the room. In the first case, his appearance to other people remains unchanged; in the second, his appearance changes from all places. In the first case, you say that it is not he who has changed, but your eyes; in the second, you say that he has changed. Generalizing, we distinguish–
(1) Cases in which only certain appearances of the object change, while others, and especially appearances from places very near to the object, do not change;
(2) Cases where all, or almost all, the appearances of the object undergo a connected change.
In the first case, the change is attributed to the medium between the object and the place; in the second, it is attributed to the object itself.*
* The application of this distinction to motion raises complications due to relativity, but we may ignore these for our present purposes.
It is the frequency of the latter kind of change, and the comparatively simple nature of the laws governing the simultaneous alterations of appearances in such cases, that have made it possible to treat a physical object as one thing, and to overlook the fact that it is a system of particulars. When a number of people at a theatre watch an actor, the changes in their several perspectives are so similar and so closely correlated that all are popularly regarded as identical with each other and with the changes of the actor himself. So long as all the changes in the appearances of a body are thus correlated there is no pressing prima facie need to break up the system of appearances, or to realize that the body in question is not really one thing but a set of correlated particulars. It is especially and primarily such changes that physics deals with, i.e. it deals primarily with processes in which the unity of a physical object need not be broken up because all its appearances change simultaneously according to the same law–or, if not all, at any rate all from places sufficiently near to the object, with in creasing accuracy as we approach the object.
The changes in appearances of an object which are due to changes in the intervening medium will not affect, or will affect only very slightly, the appearances from places close to the object. If the appearances from sufficiently neighbouring places are either wholly un changed, or changed to a diminishing extent which has zero for its limit, it is usually found that the changes can be accounted for by changes in objects which are between the object in question and the places from which its appearance has changed appreciably. Thus physics is able to reduce the laws of most changes with which it deals to changes in physical objects, and to state most of its fundamental laws in terms of matter. It is only in those cases in which the unity of the system of appearances constituting a piece of matter has to be broken up, that the statement of what is happening cannot be made exclusively in terms of matter. The whole of psychology, we shall find, is included among such cases; hence their importance for our purposes.
We can now begin to understand one of the fundamental differences between physics and psychology. Physics treats as a unit the whole system of appearances of a piece of matter, whereas psychology is interested in certain of these appearances themselves. Confining ourselves for the moment to the psychology of perceptions, we observe that perceptions are certain of the appearances of physical objects. From the point of view that we have been hitherto adopting, we might define them as the appearances of objects at places from which sense-organs and the suitable parts of the nervous system form part of the intervening medium. Just as a photographic plate receives a different impression of a cluster of stars when a telescope is part of the intervening medium, so a brain receives a different impression when an eye and an optic nerve are part of the intervening medium. An impression due to this sort of intervening medium is called a perception, and is interesting to psychology on its own account, not merely as one of the set of correlated particulars which is the physical object of which (as we say) we are having a perception.
We spoke earlier of two ways of classifying particulars. One way collects together the appearances commonly regarded as a given object from different places; this is, broadly speaking, the way of physics, leading to the construction of physical objects as sets of such appearances. The other way collects together the appearances of different objects from a given place, the result being what we call a perspective. In the particular case where the place concerned is a human brain, the perspective belonging to the place consists of all the perceptions of a certain man at a given time. Thus classification by perspectives is relevant to psychology, and is essential in defining what we mean by one mind.
I do not wish to suggest that the way in which I have been defining perceptions is the only possible way, or even the best way. It is the way that arose naturally out of our present topic. But when we approach psychology from a more introspective standpoint, we have to distinguish sensations and perceptions, if possible, from other mental occurrences, if any. We have also to consider the psychological effects of sensations, as opposed to their physical causes and correlates. These problems are quite distinct from those with which we have been concerned in the present lecture, and I shall not deal with them until a later stage.
It is clear that psychology is concerned essentially with actual particulars, not merely with systems of particulars. In this it differs from physics, which, broadly speaking, is concerned with the cases in which all the particulars which make up one physical object can be treated as a single causal unit, or rather the particulars which are sufficiently near to the object of which they are appearances can be so treated. The laws which physics seeks can, broadly speaking, be stated by treating such systems of particulars as causal units. The laws which psychology seeks cannot be so stated, since the particulars themselves are what interests the psychologist. This is one of the fundamental differences between physics and psychology; and to make it clear has been the main purpose of this lecture.
I will conclude with an attempt to give a more precise definition of a piece of matter. The appearances of a piece of matter from different places change partly according to intrinsic laws (the laws of perspective, in the case of visual shape), partly according to the nature of the intervening medium–fog, blue spectacles, telescopes, microscopes, sense-organs, etc. As we approach nearer to the object, the effect of the intervening medium grows less. In a generalized sense, all the intrinsic laws of change of appearance may be called “laws of perspective.” Given any appearance of an object, we can construct hypothetically a certain system of appearances to which the appearance in question would belong if the laws of perspective alone were concerned. If we construct this hypothetical system for each appearance of the object in turn, the system corresponding to a given appearance x will be independent of any distortion due to the medium beyond x, and will only embody such distortion as is due to the medium between x and the object. Thus, as the appearance by which our hypothetical system is defined is moved nearer and nearer to the object, the hypothetical system of appearances defined by its means embodies less and less of the effect of the medium. The different sets of appearances resulting from moving x nearer and nearer to the object will approach to a limiting set, and this limiting set will be that system of appearances which the object would present if the laws of perspective alone were operative and the medium exercised no distorting effect. This limiting set of appearances may be defined, for purposes of physics, as the piece of matter concerned.
LECTURE VI. INTROSPECTION
One of the main purposes of these lectures is to give grounds for the belief that the distinction between mind and matter is not so fundamental as is commonly supposed. In the preceding lecture I dealt in outline with the physical side of this problem. I attempted to show that what we call a material object is not itself a substance, but is a system of particulars analogous in their nature to sensations, and in fact often including actual sensations among their number. In this way the stuff of which physical objects are composed is brought into relation with the stuff of which part, at least, of our mental life is composed.
There is, however, a converse task which is equally necessary for our thesis, and that is, to show that the stuff of our mental life is devoid of many qualities which it is commonly supposed to have, and is not possessed of any attributes which make it incapable of forming part of the world of matter. In the present lecture I shall begin the arguments for this view.
Corresponding to the supposed duality of matter and mind, there are, in orthodox psychology, two ways of knowing what exists. One of these, the way of sensation and external perception, is supposed to furnish data for our knowledge of matter, the other, called “introspection,” is supposed to furnish data for knowledge of our mental processes. To common sense, this distinction seems clear and easy. When you see a friend coming along the street, you acquire knowledge of an external, physical fact; when you realize that you are glad to meet him, you acquire knowledge of a mental fact. Your dreams and memories and thoughts, of which you are often conscious, are mental facts, and the process by which you become aware of them SEEMS to be different from sensation. Kant calls it the “inner sense”; sometimes it is spoken of as “consciousness of self”; but its commonest name in modern English psychology is “introspection.” It is this supposed method of acquiring knowledge of our mental processes that I wish to analyse and examine in this lecture.
I will state at the outset the view which I shall aim at establishing. I believe that the stuff of our mental life, as opposed to its relations and structure, consists wholly of sensations and images. Sensations are connected with matter in the way that I tried to explain in Lecture V, i.e. each is a member of a system which is a certain physical object. Images, though they USUALLY have certain characteristics, especially lack of vividness, that distinguish them from sensations, are not INVARIABLY so distinguished, and cannot therefore be defined by these characteristics. Images, as opposed to sensations, can only be defined by their different causation: they are caused by association with a sensation, not by a stimulus external to the nervous system–or perhaps one should say external to the brain, where the higher animals are concerned. The occurrence of a sensation or image does not in itself constitute knowledge but any sensation or image may come to be known if the conditions are suitable. When a sensation–like the hearing of a clap of thunder–is normally correlated with closely similar sensations in our neighbours, we regard it as giving knowledge of the external world, since we regard the whole set of similar sensations as due to a common external cause. But images and bodily sensations are not so correlated. Bodily sensations can be brought into a correlation by physiology, and thus take their place ultimately among sources of knowledge of the physical world. But images cannot be made to fit in with the simultaneous sensations and images of others. Apart from their hypothetical causes in the brain, they have a causal connection with physical objects, through the fact that they are copies of past sensations; but the physical objects with which they are thus connected are in the past, not in the present. These images remain private in a sense in which sensations are not. A sensation SEEMS to give us knowledge of a present physical object, while an image does not, except when it amounts to a hallucination, and in this case the seeming is deceptive. Thus the whole context of the two occurrences is different. But in themselves they do not differ profoundly, and there is no reason to invoke two different ways of knowing for the one and for the other. Consequently introspection as a separate kind of knowledge disappears.
The criticism of introspection has been in the main the work of American psychologists. I will begin by summarizing an article which seems to me to afford a good specimen of their arguments, namely, “The Case against Introspection,” by Knight Dunlap (“Psychological Review,” vol xix, No. 5, pp. 404-413, September, 1912). After a few historical quotations, he comes to two modern defenders of introspection, Stout and James. He quotes from Stout such statements as the following: “Psychical states as such become objects only when we attend to them in an introspective way. Otherwise they are not themselves objects, but only constituents of the process by which objects are recognized” (“Manual,” 2nd edition, p. 134. The word “recognized” in Dunlap’s quotation should be “cognized.”) “The object itself can never be identified with the present modification of the individual’s consciousness by which it is cognized” (ib. p. 60). This is to be true even when we are thinking about modifications of our own consciousness; such modifications are to be always at least partially distinct from the conscious experience in which we think of them.
At this point I wish to interrupt the account of Knight Dunlap’s article in order to make some observations on my own account with reference to the above quotations from Stout. In the first place, the conception of “psychical states” seems to me one which demands analysis of a somewhat destructive character. This analysis I shall give in later lectures as regards cognition; I have already given it as regards desire. In the second place, the conception of “objects” depends upon a certain view as to cognition which I believe to be wholly mistaken, namely, the view which I discussed in my first lecture in connection with Brentano. In this view a single cognitive occurrence contains both content and object, the content being essentially mental, while the object is physical except in introspection and abstract thought. I have already criticized this view, and will not dwell upon it now, beyond saying that “the process by which objects are cognized” appears to be a very slippery phrase. When we “see a table,” as common sense would say, the table as a physical object is not the “object” (in the psychological sense) of our perception. Our perception is made up of sensations, images and beliefs, but the supposed “object” is something inferential, externally related, not logically bound up with what is occurring in us. This question of the nature of the object also affects the view we take of self-consciousness. Obviously, a “conscious experience” is different from a physical object; therefore it is natural to assume that a thought or perception whose object is a conscious experience must be different from a thought or perception whose object is a physical object. But if the relation to the object is inferential and external, as I maintain, the difference between two thoughts may bear very little relation to the difference between their objects. And to speak of “the present modification of the individual’s consciousness by which an object is cognized” is to suggest that the cognition of objects is a far more direct process, far more intimately bound up with the objects, than I believe it to be. All these points will be amplified when we come to the analysis of knowledge, but it is necessary briefly to state them now in order to suggest the atmosphere in which our analysis of “introspection” is to be carried on.
Another point in which Stout’s remarks seem to me to suggest what I regard as mistakes is his use of “consciousness.” There is a view which is prevalent among psychologists, to the effect that one can speak of “a conscious experience” in a curious dual sense, meaning, on the one hand, an experience which is conscious of something, and, on the other hand, an experience which has some intrinsic nature characteristic of what is called “consciousness.” That is to say, a “conscious experience” is characterized on the one hand by relation to its object and on the other hand by being composed of a certain peculiar stuff, the stuff of “consciousness.” And in many authors there is yet a third confusion: a “conscious experience,” in this third sense, is an experience of which we are conscious. All these, it seems to me, need to be clearly separated. To say that one occurrence is “conscious” of another is, to my mind, to assert an external and rather remote relation between them. I might illustrate it by the relation of uncle and nephew a man becomes an uncle through no effort of his own, merely through an occurrence elsewhere. Similarly, when you are said to be “conscious” of a table, the question whether this is really the case cannot be decided by examining only your state of mind: it is necessary also to ascertain whether your sensation is having those correlates which past experience causes you to assume, or whether the table happens, in this case, to be a mirage. And, as I explained in my first lecture, I do not believe that there is any “stuff” of consciousness, so that there is no intrinsic character by which a “conscious” experience could be distinguished from any other.
After these preliminaries, we can return to Knight Dunlap’s article. His criticism of Stout turns on the difficulty of giving any empirical meaning to such notions as the “mind” or the “subject”; he quotes from Stout the sentence: “The most important drawback is that the mind, in watching its own workings, must necessarily have its attention divided between two objects,” and he concludes: “Without question, Stout is bringing in here illicitly the concept of a single observer, and his introspection does not provide for the observation of this observer; for the process observed and the observer are distinct” (p. 407). The objections to any theory which brings in the single observer were considered in Lecture I, and were acknowledged to be cogent. In so far, therefore, as Stout’s theory of introspection rests upon this assumption, we are compelled to reject it. But it is perfectly possible to believe in introspection without supposing that there is a single observer.
William James’s theory of introspection, which Dunlap next examines, does not assume a single observer. It changed after the publication of his “Psychology,” in consequence of his abandoning the dualism of thought and things. Dunlap summarizes his theory as follows:
“The essential points in James’s scheme of consciousness are SUBJECT, OBJECT,and a KNOWING of the object by the subject. The difference between James’s scheme and other schemes involving the same terms is that James considers subject and object to be the same thing, but at different times In order to satisfy this requirement James supposes a realm of existence which he at first called ‘states of consciousness’ or ‘thoughts,’ and later, ‘pure experience,’ the latter term including both the ‘thoughts’ and the ‘knowing.’ This scheme, with all its magnificent artificiality, James held on to until the end, simply dropping the term consciousness and the dualism between the thought and an external reality”(p. 409).
He adds: “All that James’s system really amounts to is the acknowledgment that a succession of things are known, and that they are known by something. This is all any one can claim, except for the fact that the things are known together, and that the knower for the different items is one and the same” (ib.).
In this statement, to my mind, Dunlap concedes far more than James did in his later theory. I see no reason to suppose that “the knower for different items is one and the same,” and I am convinced that this proposition could not possibly be ascertained except by introspection of the sort that Dunlap rejects. The first of these points must wait until we come to the analysis of belief: the second must be considered now. Dunlap’s view is that there is a dualism of subject and object, but that the subject can never become object, and therefore there is no awareness of an awareness. He says in discussing the view that introspection reveals the occurrence of knowledge: “There can be no denial of the existence of the thing (knowing) which is alleged to be known or observed in this sort of ‘introspection.’ The allegation that the knowing is observed is that which may be denied. Knowing there certainly is; known, the knowing certainly is not”(p. 410). And again: “I am never aware of an awareness” (ib.). And on the next page: “It may sound paradoxical to say that one cannot observe the process (or relation) of observation, and yet may be certain that there is such a process: but there is really no inconsistency in the saying. How do I know that there is awareness? By being aware of something. There is no meaning in the term ‘awareness’ which is not expressed in the statement ‘I am aware of a colour (or what-not).’ “
But the paradox cannot be so lightly disposed of. The statement “I am aware of a colour” is assumed by Knight Dunlap to be known to be true, but he does not explain how it comes to be known. The argument against him is not conclusive, since he may be able to show some valid way of inferring our awareness. But he does not suggest any such way. There is nothing odd in the hypothesis of beings which are aware of objects, but not of their own awareness; it is, indeed, highly probable that young children and the higher animals are such beings. But such beings cannot make the statement “I am aware of a colour,” which WE can make. We have, therefore, some knowledge which they lack. It is necessary to Knight Dunlap’s position to maintain that this additional knowledge is purely inferential, but he makes no attempt to show how the inference is possible. It may, of course, be possible, but I cannot see how. To my mind the fact (which he admits) that we know there is awareness, is ALL BUT decisive against his theory, and in favour of the view that we can be aware of an awareness.
Dunlap asserts (to return to James) that the real ground for James’s original belief in introspection was his belief in two sorts of objects, namely, thoughts and things. He suggests that it was a mere inconsistency on James’s part to adhere to introspection after abandoning the dualism of thoughts and things. I do not wholly agree with this view, but it is difficult to disentangle the difference as to introspection from the difference as to the nature of knowing. Dunlap suggests (p. 411) that what is called introspection really consists of awareness of “images,” visceral sensations, and so on. This view, in essence, seems to me sound. But then I hold that knowing itself consists of such constituents suitably related, and that in being aware of them we are sometimes being aware of instances of knowing. For this reason, much as I agree with his view as to what are the objects of which there is awareness, I cannot wholly agree with his conclusion as to the impossibility of introspection.
The behaviourists have challenged introspection even more vigorously than Knight Dunlap, and have gone so far as to deny the existence of images. But I think that they have confused various things which are very commonly confused, and that it is necessary to make several distinctions before we can arrive at what is true and what false in the criticism of introspection.
I wish to distinguish three distinct questions, any one of which may be meant when we ask whether introspection is a source of knowledge. The three questions are as follows:
(1) Can we observe anything about ourselves which we cannot observe about other people, or is everything we can observe PUBLIC, in the sense that another could also observe it if suitably placed?
(2) Does everything that we can observe obey the laws of physics and form part of the physical world, or can we observe certain things that lie outside physics?
(3) Can we observe anything which differs in its intrinsic nature from the constituents of the physical world, or is everything that we can observe composed of elements intrinsically similar to the constituents of what is called matter?
Any one of these three questions may be used to define introspection. I should favour introspection in the sense of the first question, i.e. I think that some of the things we observe cannot, even theoretically, be observed by any one else. The second question, tentatively and for the present, I should answer in favour of introspection; I think that images, in the actual condition of science, cannot be brought under the causal laws of physics, though perhaps ultimately they may be. The third question I should answer adversely to introspection I think that observation shows us nothing that is not composed of sensations and images, and that images differ from sensations in their causal laws, not intrinsically. I shall deal with the three questions successively.
(1) PUBLICITY OR PRIVACY OF WHAT IS OBSERVED. Confining ourselves, for the moment, to sensations, we find that there are different degrees of publicity attaching to different sorts of sensations. If you feel a toothache when the other people in the room do not, you are in no way surprised; but if you hear a clap of thunder when they do not, you begin to be alarmed as to your mental condition. Sight and hearing are the most public of the senses; smell only a trifle less so; touch, again, a trifle less, since two people can only touch the same spot successively, not simultaneously. Taste has a sort of semi-publicity, since people seem to experience similar taste-sensations when they eat similar foods; but the publicity is incomplete, since two people cannot eat actually the same piece of food.
But when we pass on to bodily sensations–headache, toothache, hunger, thirst, the feeling of fatigue, and so on–we get quite away from publicity, into a region where other people can tell us what they feel, but we cannot directly observe their feeling. As a natural result of this state of affairs, it has come to be thought that the public senses give us knowledge of the outer world, while the private senses only give us knowledge as to our own bodies. As regards privacy, all images, of whatever sort, belong with the sensations which only give knowledge of our own bodies, i.e. each is only observable by one observer. This is the reason why images of sight and hearing are more obviously different from sensations of sight and hearing than images of bodily sensations are from bodily sensations; and that is why the argument in favour of images is more conclusive in such cases as sight and hearing than in such cases as inner speech.
The whole distinction of privacy and publicity, however, so long as we confine ourselves to sensations, is one of degree, not of kind. No two people, there is good empirical reason to think, ever have exactly similar sensations related to the same physical object at the same moment; on the other hand, even the most private sensation has correlations which would theoretically enable another observer to infer it.
That no sensation is ever completely public, results from differences of point of view. Two people looking at the same table do not get the same sensation, because of perspective and the way the light falls. They get only correlated sensations. Two people listening to the same sound do not hear exactly the same thing, because one is nearer to the source of the sound than the other, one has better hearing than the other, and so on. Thus publicity in sensations consists, not in having PRECISELY similar sensations, but in having more or less similar sensations correlated according to ascertainable laws. The sensations which strike us as public are those where the correlated sensations are very similar and the correlations are very easy to discover. But even the most private sensations have correlations with things that others can observe. The dentist does not observe your ache, but he can see the cavity which causes it, and could guess that you are suffering even if you did not tell him. This fact, however, cannot be used, as Watson would apparently wish, to extrude from science observations which are private to one observer, since it is by means of many such observations that correlations are established, e.g. between toothaches and cavities. Privacy, therefore does not by itself make a datum unamenable to scientific treatment. On this point, the argument against introspection must be rejected.
(2) DOES EVERYTHING OBSERVABLE OBEY THE LAWS OF PHYSICS? We come now to the second ground of objection to introspection, namely, that its data do not obey the laws of physics. This, though less emphasized, is, I think, an objection which is really more strongly felt than the objection of privacy. And we obtain a definition of introspection more in harmony with usage if we define it as observation of data not subject to physical laws than if we define it by means of privacy. No one would regard a man as introspective because he was conscious of having a stomach ache. Opponents of introspection do not mean to deny the obvious fact that we can observe bodily sensations which others cannot observe. For example, Knight Dunlap contends that images are really muscular contractions,* and evidently regards our awareness of muscular contractions as not coming under the head of introspection. I think it will be found that the essential characteristic of introspective data, in the sense which now concerns us, has to do with LOCALIZATION: either they are not localized at all, or they are localized, like visual images, in a place already physically occupied by something which would be inconsistent with them if they were regarded as part of the physical world. If you have a visual image of your friend sitting in a chair which in fact is empty, you cannot locate the image in your body, because it is visual, nor (as a physical phenomenon) in the chair, because the chair, as a physical object, is empty. Thus it seems to follow that the physical world does not include all that we are aware of, and that images, which are introspective data, have to be regarded, for the present, as not obeying the laws of physics; this is, I think, one of the chief reasons why an attempt is made to reject them. I shall try to show in Lecture VIII that the purely empirical reasons for accepting images are overwhelming. But we cannot be nearly so certain that they will not ultimately be brought under the laws of physics. Even if this should happen, however, they would still be distinguishable from sensations by their proximate causal laws, as gases remain distinguishable from solids.
* “Psychological Review,” 1916, “Thought-Content and Feeling,” p. 59. See also ib., 1912, “The Nature of Perceived Relations,” where he says: “‘Introspection,’ divested of its mythological suggestion of the observing of consciousness, is really the observation of bodily sensations (sensibles) and feelings (feelables)”(p. 427 n.).
(3) CAN WE OBSERVE ANYTHING INTRINSICALLY DIFFERENT FROM SENSATIONS? We come now to our third question concerning introspection. It is commonly thought that by looking within we can observe all sorts of things that are radically different from the constituents of the physical world, e.g. thoughts, beliefs, desires, pleasures, pains and emotions. The difference between mind and matter is increased partly by emphasizing these supposed introspective data, partly by the supposition that matter is composed of atoms or electrons or whatever units physics may at the moment prefer. As against this latter supposition, I contend that the ultimate constituents of matter are not atoms or electrons, but sensations, and other things similar to sensations as regards extent and duration. As against the view that introspection reveals a mental world radically different from sensations, I propose to argue that thoughts, beliefs, desires, pleasures, pains and emotions are all built up out of sensations and images alone, and that there is reason to think that images do not differ from sensations in their intrinsic character. We thus effect a mutual rapprochement of mind and matter, and reduce the ultimate data of introspection (in our second sense) to images alone. On this third view of the meaning of introspection, therefore, our decision is wholly against it.
There remain two points to be considered concerning introspection. The first is as to how far it is trustworthy; the second is as to whether, even granting that it reveals no radically different STUFF from that revealed by what might be called external perception, it may not reveal different RELATIONS, and thus acquire almost as much importance as is traditionally assigned to it.
To begin with the trustworthiness of introspection. It is common among certain schools to regard the knowledge of our own mental processes as incomparably more certain than our knowledge of the “external” world; this view is to be found in the British philosophy which descends from Hume, and is present, somewhat veiled, in Kant and his followers. There seems no reason whatever to accept this view. Our spontaneous, unsophisticated beliefs, whether as to ourselves or as to the outer world, are always extremely rash and very liable to error. The acquisition of caution is equally necessary and equally difficult in both directions. Not only are we often un aware of entertaining a belief or desire which exists in us; we are often actually mistaken. The fallibility of introspection as regards what we desire is made evident by psycho-analysis; its fallibility as to what we know is easily demonstrated. An autobiography, when confronted by a careful editor with documentary evidence, is usually found to be full of obviously inadvertent errors. Any of us confronted by a forgotten letter written some years ago will be astonished to find how much more foolish our opinions were than we had remembered them as being. And as to the analysis of our mental operations–believing, desiring, willing, or what not–introspection unaided gives very little help: it is necessary to construct hypotheses and test them by their consequences, just as we do in physical science. Introspection, therefore, though it is one among our sources of knowledge, is not, in isolation, in any degree more trustworthy than “external” perception.
I come now to our second question: Does introspection give us materials for the knowledge of relations other than those arrived at by reflecting upon external perception? It might be contended that the essence of what is “mental” consists of relations, such as knowing for example, and that our knowledge concerning these essentially mental relations is entirely derived from introspection. If “knowing” were an unanalysable relation, this view would be incontrovertible, since clearly no such relation forms part of the subject matter of physics. But it would seem that “knowing” is really various relations, all of them complex. Therefore, until they have been analysed, our present question must remain unanswered I shall return to it at the end of the present course of lectures.
LECTURE VII. THE DEFINITION OF PERCEPTION
In Lecture V we found reason to think that the ultimate constituents* of the world do not have the characteristics of either mind or matter as ordinarily understood: they are not solid persistent objects moving through space, nor are they fragments of “consciousness.” But we found two ways of grouping particulars, one into “things” or “pieces of matter,” the other into series of “perspectives,” each series being what may be called a “biography.” Before we can define either sensations or images, it is necessary to consider this twofold classification in somewhat greater detail, and to derive from it a definition of perception. It should be said that, in so far as the classification assumes the whole world of physics (including its unperceived portions), it contains hypothetical elements. But we will not linger on the grounds for admitting these, which belong to the philosophy of physics rather than of psychology.
* When I speak of “ultimate constituents,” I do not mean necessarily such as are theoretically incapable of analysis, but only such as, at present, we can see no means of analysing. I speak of such constituents as “particulars,” or as “RELATIVE particulars” when I wish to emphasize the fact that they may be themselves complex.
The physical classification of particulars collects together all those that are aspects of one “thing.” Given any one particular, it is found often (we do not say always) that there are a number of other particulars differing from this one in gradually increasing degrees. Those (or some of those) that differ from it only very slightly will be found to differ approximately according to certain laws which may be called, in a generalized sense, the laws of “perspective”; they include the ordinary laws of perspective as a special case. This approximation grows more and more nearly exact as the difference grows less; in technical language, the laws of perspective account for the differences to the first order of small quantities, and other laws are only required to account for second-order differences. That is to say, as the difference diminishes, the part of the difference which is not according to the laws of perspective diminishes much more rapidly, and bears to the total difference a ratio which tends towards zero as both are made smaller and smaller. By this means we can theoretically collect together a number of particulars which may be defined as the “aspects” or “appearances” of one thing at one time. If the laws of perspective were sufficiently known, the connection between different aspects would be expressed in differential equations.
This gives us, so far, only those particulars which constitute one thing at one time. This set of particulars may be called a “momentary thing.” To define that series of “momentary things” that constitute the successive states of one thing is a problem involving the laws of dynamics. These give the laws governing the changes of aspects from one time to a slightly later time, with the same sort of differential approximation to exactness as we obtained for spatially neighbouring aspects through the laws of perspective. Thus a momentary thing is a set of particulars, while a thing (which may be identified with the whole history of the thing) is a series of such sets of particulars. The particulars in one set are collected together by the laws of perspective; the successive sets are collected together by the laws of dynamics. This is the view of the world which is appropriate to traditional physics.
The definition of a “momentary thing” involves problems concerning time, since the particulars constituting a momentary thing will not be all simultaneous, but will travel outward from the thing with the velocity of light (in case the thing is in vacuo). There are complications connected with relativity, but for our present purpose they are not vital, and I shall ignore them.
Instead of first collecting together all the particulars constituting a momentary thing, and then forming the series of successive sets, we might have first collected together a series of successive aspects related by the laws of dynamics, and then have formed the set of such series related by the laws of perspective. To illustrate by the case of an actor on the stage: our first plan was to collect together all the aspects which he presents to different spectators at one time, and then to form the series of such sets. Our second plan is first to collect together all the aspects which he presents successively to a given spectator, and then to do the same thing for the other spectators, thus forming a set of series instead of a series of sets. The first plan tells us what he does; the second the impressions he produces. This second way of classifying particulars is one which obviously has more relevance to psychology than the other. It is partly by this second method of classification that we obtain definitions of one “experience” or “biography” or “person.” This method of classification is also essential to the definition of sensations and images, as I shall endeavour to prove later on. But we must first amplify the definition of perspectives and biographies.
In our illustration of the actor, we spoke, for the moment, as though each spectator’s mind were wholly occupied by the one actor. If this were the case, it might be possible to define the biography of one spectator as a series of successive aspects of the actor related according to the laws of dynamics. But in fact this is not the case. We are at all times during our waking life receiving a variety of impressions, which are aspects of a variety of things. We have to consider what binds together two simultaneous sensations in one person, or, more generally, any two occurrences which forte part of one experience. We might say, adhering to the standpoint of physics, that two aspects of different things belong to the same perspective when they are in the same place. But this would not really help us, since a “place” has not yet been defined. Can we define what is meant by saying that two aspects are “in the same place,” without introducing anything beyond the laws of perspective and dynamics?
I do not feel sure whether it is possible to frame such a definition or not; accordingly I shall not assume that it is possible, but shall seek other characteristics by which a perspective or biography may be defined.
When (for example) we see one man and hear another speaking at the same time, what we see and what we hear have a relation which we can perceive, which makes the two together form, in some sense, one experience. It is when this relation exists that two occurrences become associated. Semon’s “engram” is formed by all that we experience at one time. He speaks of two parts of this total as having the relation of “Nebeneinander” (M. 118; M.E. 33 ff.), which is reminiscent of Herbart’s “Zusammen.” I think the relation may be called simply “simultaneity.” It might be said that at any moment all sorts of things that are not part of my experience are happening in the world, and that therefore the relation we are seeking to define cannot be merely simultaneity. This, however, would be an error–the sort of error that the theory of relativity avoids. There is not one universal time, except by an elaborate construction; there are only local times, each of which may be taken to be the time within one biography. Accordingly, if I am (say) hearing a sound, the only occurrences that are, in any simple sense, simultaneous with my sensation are events in my private world, i.e. in my biography. We may therefore define the “perspective” to which the sensation in question belongs as the set of particulars that are simultaneous with this sensation. And similarly we may define the “biography” to which the sensation belongs as the set of particulars that are earlier or later than, or simultaneous with, the given sensation. Moreover, the very same definitions can be applied to particulars which are not sensations. They are actually required for the theory of relativity, if we are to give a philosophical explanation of what is meant by “local time” in that theory The relations of simultaneity and succession are known to us in our own experience; they may be analysable, but that does not affect their suitability for defining perspectives and biographies. Such time-relations as can be constructed between events in different biographies are of a different kind: they are not experienced, and are merely logical, being designed to afford convenient ways of stating the correlations between different biographies.
It is not only by time-relations that the parts of one biography are collected together in the case of living beings. In this case there are the mnemic phenomena which constitute the unity of one “experience,” and transform mere occurrences into “experiences.” I have already dwelt upon the importance of mnemic phenomena for psychology, and shall not enlarge upon them now, beyond observing that they are what transforms a biography (in our technical sense) into a life. It is they that give the continuity of a “person” or a “mind.” But there is no reason to suppose that mnemic phenomena are associated with biographies except in the case of animals and plants.
Our two-fold classification of particulars gives rise to the dualism of body and biography in regard to everything in the universe, and not only in regard to living things. This arises as follows. Every particular of the sort considered by physics is a member of two groups (1) The group of particulars constituting the other aspects of the same physical object; (2) The group of particulars that have direct time-relations to the given particular.
Each of these is associated with a place. When I look at a star, my sensation is (1) A member of the group of particulars which is the star, and which is associated with the place where the star is; (2) A member of the group of particulars which is my biography, and which is associated with the place where I am.*
*I have explained elsewhere the manner in which space is constructed on this theory, and in which the position of a perspective is brought into relation with the position of a physical object (“Our Knowledge of the External World,” Lecture III, pp. 90, 91).
The result is that every particular of the kind relevant to physics is associated with TWO places; e.g. my sensation of the star is associated with the place where I am and with the place where the star is. This dualism has nothing to do with any “mind” that I may be supposed to possess; it exists in exactly the same sense if I am replaced by a photographic plate. We may call the two places the active and passive places respectively.* Thus in the case of a perception or photograph of a star, the active place is the place where the star is, while the passive place is the place where the percipient or photographic plate is.
* I use these as mere names; I do not want to introduce any notion of “activity.”
We can thus, without departing from physics, collect together all the particulars actively at a given place, or all the particulars passively at a given place. In our own case, the one group is our body (or our brain), while the other is our mind, in so far as it consists of perceptions. In the case of the photographic plate, the first group is the plate as dealt with by physics, the second the aspect of the heavens which it photographs. (For the sake of schematic simplicity, I am ignoring various complications connected with time, which require some tedious but perfectly feasible elaborations.) Thus what may be called subjectivity in the point of view is not a distinctive peculiarity of mind: it is present just as much in the photographic plate. And the photographic plate has its biography as well as its “matter.” But this biography is an affair of physics, and has none of the peculiar characteristics by which “mental” phenomena are distinguished, with the sole exception of subjectivity.
Adhering, for the moment, to the standpoint of physics, we may define a “perception” of an object as the appearance of the object from a place where there is a brain (or, in lower animals, some suitable nervous structure), with sense-organs and nerves forming part of the intervening medium. Such appearances of objects are distinguished from appearances in other places by certain peculiarities, namely
(1) They give rise to mnemic phenomena;
(2) They are themselves affected by mnemic phenomena.
That is to say, they may be remembered and associated or influence our habits, or give rise to images, etc., and they are themselves different from what they would have been if our past experience had been different–for example, the effect of a spoken sentence upon the hearer depends upon whether the hearer knows the language or not, which is a question of past experience. It is these two characteristics, both connected with mnemic phenomena, that distinguish perceptions from the appearances of objects in places where there is no living being.
Theoretically, though often not practically, we can, in our perception of an object, separate the part which is due to past experience from the part which proceeds without mnemic influences out of the character of the object. We may define as “sensation” that part which proceeds in this way, while the remainder, which is a mnemic phenomenon, will have to be added to the sensation to make up what is called the “perception.” According to this definition, the sensation is a theoretical core in the actual experience; the actual experience is the perception. It is obvious that there are grave difficulties in carrying out these definitions, but we will not linger over them. We have to pass, as soon as we can, from the physical standpoint, which we have been hitherto adopting, to the standpoint of psychology, in which we make more use of introspection in the first of the three senses discussed in the preceding lecture.
But before making the transition, there are two points which must be made clear. First: Everything outside my own personal biography is outside my experience; therefore if anything can be known by me outside my biography, it can only be known in one of two ways
(1) By inference from things within my biography, or
(2) By some a priori principle independent of experience.
I do not myself believe that anything approaching certainty is to be attained by either of these methods, and therefore whatever lies outside my personal biography must be regarded, theoretically, as hypothesis. The theoretical argument for adopting the hypothesis is that it simplifies the statement of the laws according to which events happen in our experience. But there is no very good ground for supposing that a simple law is more likely to be true than a complicated law, though there is good ground for assuming a simple law in scientific practice, as a working hypothesis, if it explains the facts as well as another which is less simple. Belief in the existence of things outside my own biography exists antecedently to evidence, and can only be destroyed, if at all, by a long course of philosophic doubt. For purposes of science, it is justified practically by the simplification which it introduces into the laws of physics. But from the standpoint of theoretical logic it must be regarded as a prejudice, not as a well-grounded theory. With this proviso, I propose to continue yielding to the prejudice.
The second point concerns the relating of our point of view to that which regards sensations as caused by stimuli external to the nervous system (or at least to the brain), and distinguishes images as “centrally excited,” i.e. due to causes in the brain which cannot be traced back to anything affecting the sense-organs. It is clear that, if our analysis of physical objects has been valid, this way of defining sensations needs reinterpretation. It is also clear that we must be able to find such a new interpretation if our theory is to be admissible.
To make the matter clear, we will take the simplest possible illustration. Consider a certain star, and suppose for the moment that its size is negligible. That is to say, we will regard it as, for practical purposes, a luminous point. Let us further suppose that it exists only for a very brief time, say a second. Then, according to physics, what happens is that a spherical wave of light travels outward from the star through space, just as, when you drop a stone into a stagnant pond, ripples travel outward from the place where the stone hit the water. The wave of light travels with a certain very nearly constant velocity, roughly 300,000 kilometres per second. This velocity may be ascertained by sending a flash of light to a mirror, and observing how long it takes before the reflected flash reaches you, just as the velocity of sound may be ascertained by means of an echo.
What it is that happens when a wave of light reaches a given place we cannot tell, except in the sole case when the place in question is a brain connected with an eye which is turned in the right direction. In this one very special case we know what happens: we have the sensation called “seeing the star.” In all other cases, though we know (more or less hypothetically) some of the correlations and abstract properties of the appearance of the star, we do not know the appearance itself. Now you may, for the sake of illustration, compare the different appearances of the star to the conjugation of a Greek verb, except that the number of its parts is really infinite, and not only apparently so to the despairing schoolboy. In vacuo, the parts are regular, and can be derived from the (imaginary) root according to the laws of grammar, i.e. of perspective. The star being situated in empty space, it may be defined, for purposes of physics, as consisting of all those appearances which it presents in vacuo, together with those which, according to the laws of perspective, it would present elsewhere if its appearances elsewhere were regular. This is merely the adaptation of the definition of matter which I gave in an earlier lecture. The appearance of a star at a certain place, if it is regular, does not require any cause or explanation beyond the existence of the star. Every regular appearance is an actual member of the system which is the star, and its causation is entirely internal to that system. We may express this by saying that a regular appearance is due to the star alone, and is actually part of the star, in the sense in which a man is part of the human race.