Psychology: What it Is and What it Does

It is well for a man, when he seeks a clear and unbiassed opinion upon some certain matter, to forget many things, and to begin to look at it as if he knew nothing at all before.—Li Hung Chang

§ 1. Common Sense and Science.—We live in a world of values. We have material standards of comfort, and moral standards of conduct; and we eat and drink, and dress, and house our families, and educate our children, and carry on our business in life, with these standards more or less definitely before us. We approve good manners; we avoid extravagance and display; we aim at efficiency; we try to be honest; we should like to be cultivated. Everywhere and always our ordinary living implies this reference to values, to better and worse, desirable and undesirable, vulgar and refined. And that is the same thing as saying that our ordinary living is not scientific. It is not either unscientific, in the regular meaning of that word; it has nothing to do with science; it is non-scientific or extra-scientific. For science deals, not with values, but with facts. There is no good or bad, sick or well, useful or useless, in science. When the results of science are taken over into everyday life, they are transformed into values; the telegraph becomes a business necessity, the telephone a household convenience, the motor-car a means of recreation; the physician works to cure, the educator to fit for citizenship, the social reformer to correct abuses. Science itself, however, works simply to ascertain the truth, to discover the fact. Mr. H. G. Wells complains in a recent novel that no sick soul could find help or relief in a modern text-book of psychology. Of course not! Psychology is the science of mind, not the source of mental comfort or improvement. A sick soul would not go, for that matter, to a text-book of theology; it would go to some proved and trusted friend, or to some wise and tender book written by one who had himself suffered. So a sick body would betake itself, not to the physiological laboratory, but to a physician’s consulting room or to a hospital.

We live, again, in a world whose centre is ourself. This does not necessarily mean that we are all selfish; a life may be very unselfish. But whether we are selfish or unselfish, we live in a universe which revolves about the Me. Our self spreads and expands, to embrace our clothes and house and books, our family and relations, our professional competence and connection, our political and religious beliefs; we find ourselves in all these things, and they become a part of us. A famine in India is a real event and takes its place in the world only if we are made uncomfortable when we read of it, or are stirred to send in a contribution, or suspect mismanagement somewhere and think we could have done better. And this, once more, is the same thing as saying that our ordinary living is not scientific. For science, which deals with facts, is on that account impersonal and disinterested. Men of science honour Darwin, because they are human beings and live, like everyone else, in a world of values; but these same men of science are ready at any moment to test and criticise Darwin’s work with the utmost rigour; while any parts of the work that are solidly established pass without name into the structure of the science to which they belong. A text-book of chemistry is about as impersonal as anything can be, despite the fact that every observation it describes and every law it lays down was once somebody’s personal observation or discovery, and so formed part of some self-centred universe. That personal interest is irrelevant to science. It is as irrelevant to psychology as to chemistry. The psychologist has a great deal to do with his own mind; but that is because his own mind is the most easily accessible part of his subject-matter; it is not in the least because the mind happens to be his own. He does not care as psychologist—though he may care very much as human being—whether his mind is superior and talented and broad and cultivated or is the reverse of all these things; for in the first place these adjectives are all adjectives of value, and he is in search of facts; and secondly they are words of personal or individual appraisement, and he is not concerned to praise or blame himself. Nor is he concerned to trace the motives or judge the character of other men. There is a common belief that the psychologist is an uncanny person to meet, because he is always studying human nature and is able to read thoughts. This belief belongs to the non-scientific world; those who hold it fear that the psychologist will detect in them some pettiness or meanness of human nature, or will lay his finger on some unfounded enthusiasm or some unreasoned detraction that they wish to conceal. As well might they think that the physicist whom they ask to dinner will be occupied with the surface-tension of his soup or the insulating properties of his mashed potato.

If we trace the history of human thought, we find that the scientific attitude, as we have here described it, has emerged very slowly from that mixed medley of superstition and knowledge and belief and practical interest for which we have no better name than common sense. How common sense has been constituted, and how science has gradually worked its way to an independent position,—these are interesting questions; but it is plain that we cannot enter upon them in a primer of one special science. Some references for further reading will be given at the end of the chapter. Meanwhile, the important thing is to understand clearly the aims and limitations of science. Science aims at truth; it deals with facts, with the nature of things given, not with values or meanings or uses; and it deals with these materials impersonally and disinterestedly. The student of science who fails to grasp the scientific point of view will fail also to get the perspective of a scientific text-book; he will not see the wood for the trees; and he will be disappointed with what science has to offer him; he will want to know the use of all this knowledge, while science has no regard for use. The laws of psychology may be put to very many uses, in business, in education, in legal procedure, in medicine, in the ministrations of religion; but such uses are, from the psychologist’s point of view, by-products of his science; just as the nautical almanac is a by-product of astronomy, or the safety-match a by-product of chemistry, or the stamping-out of malaria a by-product of biology. These practical results may be immensely important for everyday life; but science, in its impersonal and disinterested search for facts, makes no difference between one fact and another.

§ 2. The Subject-matter of Psychology.—Psychology is the science of mind. What, then, is mind? Everybody knows that, you will say, just as everybody knows what is matter. Everybody knows, yes, in terms of common sense; but we have seen that common sense is not science. Besides, common sense is not articulate; it cannot readily express itself; and it is a little afraid of plain statements. Close this book, now, and write down what you take mind to be; give yourself plenty of time; when you have finished, go over what you have written, and ask yourself if you really know what all the words and phrases mean, if you can define them or stand an examination on them; the exercise will be worth while.

Open the book again! The exercise was worth while; but it was not quite fair. For the fact is that these great comprehensive words that we all use and all understand cannot be rigorously defined; they are too old; they have lived through too many changes; they have gathered about them too many conflicting associations. They pass muster in our everyday discourse only because we take them for granted and do not scrutinise them too closely. The expert alone can say what common sense means by mind; and even the expert must speak in general terms, qualifying and with reservations.

It seems, however, that the prime factor in the common-sense notion of mind is the idea of activity. We ascribe to mind the same sort of voluntary and purposeful activity that we ascribe to our fellow-men; and we distinguish this activity from the blind necessity of cause and effect. We find ourselves, and those about us, deliberating, intending, resolving, planning, recalling, doubting; and we say that these and similar activities are activities of mind. We also find ourselves, and those about us, breathing, secreting, moving; but here we draw distinctions. Breathing, we say, is a physical affair, though we may hold the breath by an act of will. Secretion results from some physical or chemical cause; only if we cry for sorrow or sweat for fear is mind influencing body. Walking and blinking may be physical only; but if we turn our steps by intention into a certain path, or blink on purpose to clear our sight, the physical movements become subject to the action of mind.

So long as we stick to examples, all this seems straightforward; only it is not easy to decide whether mind is activity, or whether these various activities are activities of mind. On the whole, common sense leans to the latter view: the activities are manifestations of mind. Mind itself is then something immaterial, lying behind the manifestations. What sort of thing? Apparently, another human being, an inner man that dwells within the outer man, an insubstantial mannikin living inside the head. Does that sound absurd? But it did not seem absurd just now to read that we ascribe to mind the same sort of voluntary and purposeful activity that we ascribe to our fellow-men; and how could we do that unless mind were something like a human being? This inner man appears, in fact, to be the mind of common sense; the inner man thinks, reflects, remembers, desires; he is influenced by the outer man, becoming gloomy and morose when his host cannot digest; and he influences the outer man, who sheds tears when his inmate is grieved. A curious view, when we write it out and think of it in cold logic; but a view that we should understand if we traced the growth of common sense from its first beginnings; and a view of highly respectable antiquity. Very ancient superstitions are connected with the man who is seen in the eye; the Egyptian ka or spirit-double is a smaller copy of the outer man; Greek vase-paintings show the human soul as a tiny human being; primitive thought has from time immemorial explained, and the modern savage still explains, the life and motion of man, or his repose in sleep and death, by the presence or absence of the little creature normally at work within him.

Yet however natural a view like this may be, science can make nothing of it. For one thing, it merely pushes the problem a step further back. The inner man acts on the outer man and is acted on by him; but who or what gives the inner man, in his turn, the power to influence and to be influenced? We must suppose an endless nest of mannikins. That and other such arguments apart, however, the view is non-scientific because it offers an interpretation and not a description of mind. The mind with which psychology deals must be a mind that is describable in terms of observed fact; otherwise it cannot form the subject-matter of a science. So we must start afresh, and ask what mind is, when mind is looked at from the scientific point of view.

You will better understand the answer to this question when you have worked through the book. The answer will then have been given in the concrete and particular; now it can be given only in the abstract and general. Remember that it is given, nevertheless, in terms of work done and results obtained; it is not an answer that the psychologist makes up beforehand, but one that he himself has been led to in the course of his attempt to work scientifically upon mind. In brief it is this.

We find that the field of science has been surveyed from two different standpoints. Men of science have set out, on the one hand, to describe the world as it would be with man left out. The result is what we call physical science. The world of physics is colourless, toneless, neither cold nor warm; its spaces are always of the same extent, its times are always of the same duration, its mass is invariable; it would be just what it is now if mankind were swept from the face of the earth. For what is light in the text-books of physics?—a train of electromagnetic waves; and sound is a vibratory motion of air or water; and heat is a dance of molecules; and all these things are independent of man. But men of science have tried, on the other hand, to describe the world as it is in man’s experience, as it appears with man left in; and the result of this endeavour is psychology. The world of psychology contains looks and tones and feels; it is the world of dark and light, of noise and silence, of rough and smooth; its space is sometimes large and sometimes small, as everyone knows who in adult life has gone back to his childhood’s home; its time is sometimes short and sometimes long; it has no invariables. It contains also the thoughts, emotions, memories, imaginations, volitions that you naturally ascribe to mind; it contains, that is, so much of these things as belongs to the sphere of observable fact. It is obviously very different from the world of physics, though both worlds alike have been opened up to us by science, by the impersonal and disinterested search for facts.

So we have a world of matter and a world of mind. The physicist, however, describes and measures the various phases of energy, without assuming any material substance in the background, any matter of which this energy is the manifestation. Matter, if the word is to be used at all, is simply the inclusive name for all the forms of energy. And the psychologist, in the same way, describes and measures—so far as he is able to measure—the phenomena of his world, without assuming any active or perduring mind in the background; for him, mind is simply the inclusive name of all these phenomena. That is the first rough answer to our question. Much more must be said, if the answer is to be precise; but even as it is we have travelled a long way from the little man living inside the head!

§ 3. Mind and Body.—The first thing to get clear about is the nature of the man left in the world, the man whose presence is necessary for psychology and unnecessary for physics. Since we are talking science, this man will be man as science views him, and not the man of common sense; he will be, that is, the organism known to biology as homo sapiens, and not the self-centred person whom we meet in the everyday world of values. But the human organism owes its organic character, the organisation of its parts into a single whole, to its nervous system. All over the body and all through the body are dotted sense-organs, which take up physical and chemical impressions from their surroundings; these impressions are transmitted along nerve-fibres to the brain; in the brain they are grouped, arranged, supplemented, arrested, modified in all sorts of ways; and finally, it may be after radical transformation in the brain, they issue along other nerve-fibres to the muscles and glands. The nervous system thus receives, elaborates, and emits. Moreover, there is strong evidence to show that the world which psychology explores depends for its existence upon the functioning of the nervous system; or, if we prefer a stricter formula, that this world is correlated with the functioning of the nervous system. The man left in thus reduces to a nervous system; and that is the truth of the statement, often met with in popular scientific writing, that the brain is the organ of mind. There is no organ of mind; that phrase is an echo of the old-world search after the place of residence of the mannikin-mind, which was assigned variously to heart, liver, eye, brain, blood, or was supposed somehow to perfuse the whole body. The scientific fact is that, whenever we come upon mental phenomena, then we also find a functional nervous system; we know nothing of the former apart from the latter; the two orders are thus correlated.

The fact of this correlation has been established by two principal lines of evidence. In the first place, we find all through the animal kingdom that size of brain and complexity of nervous system are matched by range and complexity of mental phenomena. The brain of man is, by absolute measurement, an organ of great size; it is heavier than that of any other animal with the exception of a few of the very largest (such as the elephant); and in these cases the superior weight is due, not to superior development of the elaborating part of the brain, but to the bulk of the receiving and emitting portions, which are of a size to correspond with the bulk of the body. The brain of man is also relatively, as compared with the weight of the whole body, heavier than the brain of any other animal with the exception of a few of the most highly developed small mammals (such as certain monkeys); and in these cases again the superiority depends on the bulk of the receiving and emitting portions of the brain, which reflect the keen sensitivity and muscular agility of the animal. We know, on the other side, that the mental life of man is richer than that of any other creature. Secondly, we find that disturbance of certain parts of the brain indicates a certain form of mental disturbance; and, conversely, that particular forms of mental disturbance indicate disturbance of particular parts of the brain. One may become blind from injury to the brain as well as from such defect of the eye as prevents optical impressions from reaching the brain.

These are the two lines of evidence. How, though, you may now ask, do we know anything about the distribution of mental phenomena in the animal kingdom? How do we know that the lower animals live in mental worlds? and still more how can we say anything as to the nature of the phenomena that make up those worlds?

Consider first the case of your fellow-men. You do not doubt that they have experiences like your own; you take them for granted, accept them instinctively as your kin, and are able—the better as you know them better—to put yourself in their place. If, however, you had to argue the matter with a sceptic, you would point to the facts of our common life. Man’s family life, social life, civic life, national life, is based on the assumption that human experience is alike for everyone, and would be impossible if the assumption were falsified by the facts. All these forms of life, for instance, presuppose language and laws; and language and laws necessarily imply a community of experience. You would point, also, to likeness of physical organisation, likeness of sense-organs and nervous system; and you would point, lastly, to conduct or behaviour. When you feel in a certain way, you act in a certain way; your behaviour expresses your feeling; and when, under the same circumstances, a creature of like organisation regularly acts in the same way, you have a right to infer that this creature has a like feeling.

Now consider the higher animals. They possess a physical organisation closely resembling that of man. They also behave in ways that appear to express feeling. If you were familiar only with their structure, with their sense-organs and nervous system, you would be ready to endow them with mind; if you knew them only by their behaviour, you would reach the same conclusion; since you may know both, and may therefore correlate physical structure with conduct, you are able to form a fairly accurate idea of their mental world. But as you go down the scale of life, difficulties arise. The nervous system changes its type, and presently disappears; and behaviour becomes equivocal, so that students of behaviour dispute whether it is still expressive or is purely mechanical. The controversy is even carried over from the animals to the plants; there are psychologists who seriously attribute a mental life to plants. Be that as it may, the important point for us is that, as the nervous system simplifies, so does all available evidence indicate that the world of mind simplifies with it; and if mind extends further down the line of life than the nervous system, we have merely to change the wording of our general statement; we must expand it, and say that, throughout the realm of life, size and complexity of the nervous system, or of that vital mechanism which precedes the nervous system and anticipates its functions, are matched by range and complexity of mental phenomena.

The nature of these phenomena cannot be set forth with any assurance. It is difficult enough to psychologise the life of the Australian Arunta, who is our fellow-man, or of the dog who has been our companion for half-a-dozen years. What shall we say of the spider, or the amoeba, or of sundew and eelgrass? All that we can do is to follow back the history of the sense-organs, from complex to simple, comparing as we go; and to observe how the organism behaves under given circumstances, comparing this behaviour with that of other organisms higher and lower in the scale, and bringing our comparison back again and again to its final term in our own experience. We lose a great deal when we lose the nervous system; but life, after all, is a continuous development; and the disappearance of this special structure, though it may mean that our statements become vaguer and less definite, need not make our general quest hopeless. Honesty of purpose, and a passion for knowledge, and sound scientific training will carry a man further, even in this dark continent, than the casual enquirer would deem possible.

§ 4. The Problem of Psychology.—The subject-matter of psychology, as we saw on p. 9, is the whole world as it shows itself to a scientific scrutiny with man left in. Or, to put the same thing in another way, psychology gives a scientific description of the whole range of human experience correlated with the function of the human nervous system. We have just learned, however, that there is a psychology of the lower animals, possibly even of plants; and we must therefore say that we were speaking in § 2 of the subject-matter of human psychology. This is the psychology that will occupy us in the present book. Let us now see what our actual task is. What have we to do, in order to get a scientific description of mind?

We must do what everybody does who begins to describe; we must take things piecemeal. When you are away at the seaside, and are describing your room in a letter home, you tell of exposure and windows and carpets and furniture and pictures; you break up the room into parts, and list them one by one; but you do not list at haphazard; you bring your items into such connection as will make it easy for your readers to reconstruct the room. The man of science does the same sort of thing; he analyses, and all the while he is analysing he has his eyes open for relations, for putting his elements together again as they belong. The chemist analyses water into oxygen and hydrogen, and acetic acid into carbon, oxygen, and hydrogen; and you see at once that this analysis is the first step toward a scientific description; for it reduces the compounds to their elementary components, and it shows that the two compounds have certain elements in common. But the chemist, almost in the same breath, is putting together again. The ordinary formulas for water and acetic acid, H₂O and C₂H₄O₂, indicate that; for they show the number of atoms of the various elements that are held in the compound. Chemistry also has graphic formulas, of a kind that look complicated to the outsider but that are really more instructive than the others,—formulas which show in what manner, under what laws, the atoms are bound together. Any good encyclopÆdia will give you samples.

The psychologist, now, stands before a like problem. The mental world, no less than the material, comes to us in the gross; mental phenomena are complex, often highly complex; we must reduce them to their elements, we must keep analysing till we can analyse no further, if we are to describe them in a scientific way. And here too synthesis goes hand in hand with analysis. Psychology, to be sure, does not write graphic formulas; but psychology has to show how its elements go together, to discover the laws of their connection; we shall find that tones and colours go together in very different ways. All the while that we are tearing a bit of our world apart, and finding its elements, we are trying to put those elements back again in their places and to reconstruct the original experience.

Synthesis, unfortunately, is often very difficult; and you must notice that a failure to reconstruct does not necessarily mean that the preceding analysis was wrong. A chemist may analyse a given substance into a certain number of elements, each one represented by a certain number of atoms; yet if he puts these elements together again, in the right proportions, he may—perhaps because he is now working at a different temperature—come out with another substance of different properties. His analysis was not therefore wrong; but his attempt at synthesis is a failure because he has not taken account of all the relevant circumstances. It may happen similarly in psychology that we do not know all the relevant circumstances; or it may happen that we know them but cannot control them; in such cases we cannot reconstruct. The only thing to do is then to make analysis its own test; we analyse again and again; and if the result is always the same, we are satisfied to let it stand. Children who do not know how to prove an example in arithmetic follow the same plan; if they get the same answer several times over, and if their schoolmate gets that answer too, they are satisfied; and when the work has been honestly done, the agreement is pretty good evidence that they are right.

Notice one other point: that if you sit down to describe, there is simply no escape from analysis. To begin a description is to be analysing. Well-meaning people sometimes shake their heads at scientific psychology; all this dissecting work, they say, misses the real issue; it kills mind; it destroys the living, breathing reality of experience, and offers in its place a catalogue of dead facts. The mannikin again! Of course, if mind is a little man inside you, you must kill him to dissect him,—though he nevertheless crops up again, alive and well, after the autopsy. The mannikin, as we have seen, cannot face cold logic. No, the task of science is to describe; if you are to describe you must analyse; and the results are every bit as real as the unanalysed experience. Dead facts? But a fact is the most live thing possible; it will survive any number of theories, and will still give birth to more.

Lastly, since mental phenomena are correlated with the function of the nervous system, the psychologist’s task is not complete until he has acquainted himself with the physiology of that system, and has worked out the correlation as accurately as is possible. Here, again, is something that you will better understand when you have read further in the book. For the present we will notice two points. First, the psychologist can gain access to a large part of his world only by way of the organs of sense; and it is therefore important that he know the structure and functions of these organs and their relation to the brain. Secondly, a train of mental phenomena may be guided and directed by events, occurring within the nervous system, which themselves have no counterpart in the world of mind; for, while all mental phenomena are correlated with processes in the nervous system, not all processes in the nervous system have mental phenomena to correspond with them. Unless, then, the psychologist knows the nature of these guiding events, he will be like the chemist who failed to take account of temperature; he will lack knowledge of relevant circumstances. Special books upon the nervous system have been written, giving in outline what the student of psychology needs to know; some of them are referred to at the end of the chapter; but it is an advantage to have taken a practical course in the physiology of the nervous system, and to be able to think in terms of neural processes. If you have had no such opportunity you can still learn a good deal from diagrams and verbal accounts; and you may find comfort in the assurance that there have been eminent psychologists who knew very little about the brain.

In fine, then, the problem of human psychology is threefold: to analyse mental phenomena into their elements, to discover the laws of mental connection, and to work out in detail and under all its phases the correlation of mind with nervous system.

§ 5. The Method of Psychology.—Having learned what we have to do, let us ask what method we are to follow in doing it. So far as the nervous system is concerned, it is evident that the psychologist must take his cue from the physiologist; indeed, this part of his problem makes him, for the time being, a physiologist, only that his real interest remains centred in mind. But how is it when he is attacking the other parts of the problem? Is there a special psychological method, a peculiar way of working, that he must adopt in his study of mental phenomena? The answer is No: his method is that of science in general.

This method may be summed up in a single word as observation. All scientific description, all description that reflects a disinterested and impersonal search for fact, is got by way of observation. And observation implies three things: a certain attitude towards phenomena, a vivid experience of the particular phenomenon which is the object of observation, and an adequate report of this experience in words. The relation of these three things will be clear if we write a formula for observation, thus:

psychological (vivid experience ? full report).

The adjective outside the bracket shows that we take up a psychological attitude to the world; in other words, that the world which we are exploring is (to use our catch-phrase again) the world with man left in. The adjective applies to the whole contents of the bracket; the experience which we are to have is mental experience, and our account of it is to be couched in psychological language. We are, then, ready for the experience; it comes, and we give it our best attention; we then express it in words; and we try to express it fully and adequately, in the words that it itself points to and requires. When the account has been written down, and so made available for other students, we have completed a psychological observation. When a number of such observations have been taken, we have the materials for a scientific description.

Observation is by no means easy; “there is not one person in a hundred,” said Huxley, “who can describe the commonest occurrence with even an approach to accuracy.” The reasons are partly of a technical nature; the use of scientific method is a bit of skilled labour, and skilled labour presupposes training; at first we are likely to be careless and clumsy; we do not see the need of scrupulous care, just because we do not know exactly what it is that we are doing. The great reason lies, however, in that difference between science and common sense to which we have already adverted; common sense interprets, and science describes. Malobservation is due, in the great majority of cases, to the ingrained tendency of the onlooker to interpret, to explain, what he observes. How many educated men and women to-day believe that the full moon dissipates the clouds? and how many more believe that changes of the moon coincide in some way with changes of the weather?

These remarks apply very definitely to psychology. The psychological observer needs technical training, first and foremost, because mental phenomena never stand still to be observed; mind is always in course, always going on; he must learn either to take rapid notes as the experience is passing, while he still remains alert to the new phases as they come, or he must register the experience phase by phase in memory, and reproduce it in words after it has passed. Nothing could well be more misleading, as a name for mental phenomena, than the familiar phrase ‘states of consciousness’; for a state is something relatively stable and permanent. Mental experiences are moving, proceeding, ongoing experiences; we might make up one of Lewis Carroll’s portmanteau-words, and say that their essence is a processence. We shall henceforth speak of them as mental processes; only remember that they are not processes of something or in something, like the processes of decomposition and fermentation; they are experiences whose very nature is a proceeding, a course in time.

Secondly, the psychological observer is badly handicapped by common sense, which has long drawn a distinction between the method of psychology and the method of physics. Psychology is supposed to look within, to turn its eyes inward; physics is supposed to look out upon the objective world, and to keep its eyes in their normal position. The method of psychology is then an introspection or self-contemplation, a looking-in; and the method of the physical sciences is an inspection, a looking-at. The self which is thus introspected is, of course, judged and valued and approved and blamed; we know the ear-marks of common sense. So we find that the hero of yesterday’s novel “was not given to introspection. His external interests in life were too engrossing for him to think deeply or continuously about himself. Such a habit of mind he used vehemently to deprecate as morbid, egotistical. But now”—now the fateful girl is on the scene; the hero begins to think about himself; and flatters himself, poor man, that he is turning psychologist.

Unfortunately, neither a keen appreciation of his own virtue nor a rooted distrust of his own powers makes a man into a psychologist. Science turns its back upon the world of values. If, then, we are to keep the word introspection for the method of psychology, we must write the equations:

where the adjectives outside the brackets mean simply what we have already stated them to mean. When once the initial attitude has been taken, and the world to be explored has thus been determined, the methods are the same. The beginner in psychology will however find, again and again, that his common-sense self stands in the way of disinterested observation; and as the word introspection contains a reference to this self, he may prefer to drop it altogether.

So much for observation in general! When we come to particulars, we find that science, wherever possible, has recourse to experiment. This does not mean that science renounces observation. For an experiment, if we push our definition back to fundamentals, is simply an observation that may be repeated, that may be isolated, and that may be varied. See the advantages! Repetition gives us plenty of time for observation; we need not mind overlooking something now, since we shall have the opportunity of picking it up later; and we can go on, observing and observing, until our description of the phenomenon is as complete as it can be made. Isolation makes our task easier; disturbing influences are ruled out; our attention is not distracted; we can give ourselves wholly to the matter in hand. Variation—the substituting of one factor for another in successive observations, or the emphasising in one observation of a factor that was obscure in another—helps us to clear up doubtful points; to distinguish what is universal from what is only accidental in the phenomenon we are observing; and to bring this phenomenon into relation with kindred phenomena. Repetition saves hurry and worry; isolation prevents distraction; variation keeps us from jumping at conclusions. These are the advantages of experiment; and all experiments, in physics, in chemistry, in biology, everywhere, fall under this definition.

Psychology needs the experimental method for both the reasons noted above: because the observed phenomena are elusive and slippery processes, and because the observer is warped and biassed by common sense. We may therefore show by an example how psychological experiment is possible. Suppose that we wish to find out how a printed word is perceived,—whether we read it letter by letter, or take in its form as a whole, or take in certain letters clearly and the general form vaguely. We first prepare our material. We print upon cards, or photograph upon lantern slides, a large number of words. We employ different printing types; different groups of letters; different lengths of words; single words and groups of words; words properly spelled, and words altered by mutilation or omission of particular letters at different parts of the word. Every one of these classes of stimuli, as the words may be technically called, is represented by a number of cards or slides. The stimuli are mixed in haphazard order, and are thrown upon the screen by a reflectoscope or projection lantern in an otherwise dark room; a pneumatic shutter before the lantern makes it possible to show them for a brief time, say, a fifth of a second. All this apparatus is put in the charge of an experimenter. When the material is ready, and the whole arrangement works properly, an observer is called in. He works for a limited time, at the same hour every day, and only after a certain time has been allowed for his eyes to accustom themselves to the dark. The stimuli are presented at regular intervals. The observer reports what he perceives at every exposure of a stimulus, and the experimenter writes down what he says.

It is plain, now, that these observations may be repeated. For one thing, there is a group of like cards in every class; and for another thing, the observer himself (since he works every day at the same time and under the same circumstances) is a fairly constant quantity. Besides, the observations may also be made by other observers, in other laboratories, under precisely the same circumstances; they may be repeated in just the same sense that a physical observation may be repeated. Secondly, the observations are isolated; they are made in a dark and quiet room, free from outside disturbance. No doubt, the observer’s thoughts may wander in the intervals between observations. For this reason, the experimenter gives a preconcerted signal, or calls out Now, a second or two before a word is shown; this signal warns the observer to pull himself together and to free himself from any such distractions. Thirdly, the observations are varied; for we employ all sorts of words, both normally printed and variously changed; and the stimuli may be presented for various lengths of time. Here, then, is a true psychological experiment; and if many observers, after many observations, give the same account of their perceptive experience, that account may stand as established psychological fact.

Not all mental phenomena can be subjected to experiment so neatly as this particular perception; and the psychologist must still fall back, more often than he likes, upon casual observation or imperfect experiments. The reason is that psychology has only recently become an experimental science. Common-sense psychology is very old: we have a complete treatise in Greek from the hand of Aristotle, and a text-book in Pali compiled by some Buddhist sage, both dating from the fourth century B.C. But while it is in the sixteenth century of our era that the physicist abandons scholastic speculation and begins to study nature by experiment, it is not till the last quarter of the nineteenth that the psychologist follows suit. In or about the year 1875 the late Professor James, then instructor in anatomy and physiology at Harvard, had a single room devoted to psychological apparatus and experiments; and in 1879 Professor Wundt opened at the University of Leipsic, in a very modest way, the laboratory which has since become the most famous in the world. It is true that experiments in psychology had been made by individuals long before laboratories were thought of; but the same thing is true of physics and chemistry; and we may remember, when we come to the weak places of psychological exposition, that laboratory research and instruction are not yet fifty years old.

§ 6. Process and Meaning.—Science, we said on p. 4, does not deal with values or meanings or uses, but only with facts; and we have just seen how words, which in everyday life are practically all meaning, may be made the objects of psychological experiment. Still, in their case, after all, we were simply ignoring meaning; so far as the observer was able to read words at all from the stimuli flashed on the screen, he read words which had a meaning, and a meaning that the experimenter might have discovered if he had been interested in it. We have not offered any evidence that mental processes are not intrinsically meaningful, that meaning is not an essential aspect of their nature; we have just assumed that they may be treated, scientifically, as bare facts. Let us now see whether meaning is essential to them or not. There are several heads of evidence.

First, meaning may be stripped from the mental process to which it normally belongs. Repeat aloud some word—the first that occurs to you; house, for instance—over and over again; presently the sound of the word becomes meaningless and blank; you are puzzled and a morsel frightened as you hear it. The same loss of meaning is observed in pathological cases; there are patients who can hear and see words as plainly as you can, but who are unable to understand what they hear and see; the bare perception is there, but it is bereft of its meaning.

Secondly, a meaningless experience may take on a meaning. A friend shows you a card, upon which is scrawled a tangle of lines; you cannot make head or tail of it. He tells you to look at the back; you see the date there written; you think at once of a great earthquake; you realise that the scrawl is a seismographic record. Meaning has thus been attached or added to a bare perception. Similarly, in learning a new script or a new language, you attach meaning to what was at first meaningless. The first experiments in the teaching of the blind deaf-mute Laura Bridgman “were made by pasting upon several common articles, such as keys, spoon, knives, and the like, little paper labels on which the name of the article had been printed in raised letters.” These meaningless feels, as they were at the outset, came presently to mean the objects with which the teacher had connected them.

Thirdly, an experience and its meaning may be disjoined in time. We often ask, in conversation, to have a remark repeated; we have heard without understanding; but before the speaker has time to repeat, we ourselves begin to reply; the meaning has come, but comes after an appreciable interval. So we may have to wait a little while before we can recall the meaning of some foreign word that nevertheless, as we say, we know perfectly well. This disjunction is also found in pathological cases. A patient “with slight stupor could not answer questions except very slowly. She was constantly saying: ‘I see everything, but I don’t know anything.’ It took her five minutes to tell the time when she was shown a clock.”

Here the experience comes first, and the meaning follows after. This order may, however, be reversed. You want to know the German of the proverb ‘Out of the frying pan into the fire’; you have the meaning, but you cannot think of the words; and presently the words leap to mind, aus dem Regen in die Traufe, out of the rain into the roof-drip. Or you know what you want to say, but you cannot get this meaning into words. An author who is very definitely aware of the meaning he wishes to convey to his reader may nevertheless have to write a paragraph ten or twenty times over before the sight and sound of his own words give back that meaning to himself. Or again, you may anticipate, in listening to a lecture, the meaning of what the lecturer is going to say, and yet you may be surprised at the words which he actually uses.

Fourthly, one and the same experience may have several meanings. Any dictionary is a proof of that! A lecturer may demonstrate the fact to a class by drawing on the blackboard, line by line, the figure of some such thing as, for instance, a desk-telephone. As the drawing proceeds, the lines may mean a pump, or a student lamp, or an electric portable, or a railway semaphore, or a jack, or various other things. In this case, to be sure, a single meaning is given when the drawing is complete; but there are plenty of experiences—a bit of bad handwriting, a distant object, an obscure patch in a painting—that leave us permanently unable to decide among several meanings. How often do we worry over a chance remark: it seemed to mean this, but could it have meant that, or is it possible that it really meant the other?

Fifthly, one and the same meaning may attach to several experiences. You walk into a room, and there see a table; you go into the same room in the dark and hurt yourself, and you complain that you ran against the table; you hear a noise overhead, and wish that the maid would not drag that table about. Here the meaning of a particular table is carried by three modes of perceptive experience. In certain forms of mental disorder one obsessing meaning colours all the experiences of the daily life. The patient “scents poison and treachery on all sides. He has slowly convinced himself by numerous tests in little things that he is no longer liked. The workmen are refractory and disobedient with him more than with anyone else. His chiefs and his fellows play malicious tricks upon him. His food tastes differently, and does not agree with him. When he goes to another town, it is plain that his enemies have anticipated him by writing letters to his injury.” Every experience that this man has means persecution.

Sixthly, meaning and mental process are not covariants. Richness and fullness of experience do not necessarily correspond with wealth of meaning; you may, in fact, be bewildered, and fail to find a meaning just because there is so much material to take in; your first hearing of a Wagner opera gave you, probably, more sound than sense. Conversely, poverty of experience does not necessarily mean loss or reduction of meaning; if that were the case, we could not pack so much meaning into such little things as words.

All this evidence would be greatly strengthened if we went beyond the limits of individual experience, and compared man with man, profession with profession, race with race, age with age. What is meaningless to me might be full of meaning to you; the same landscape yields different meanings to the geologist and the farmer; a protruded tongue means insult here, but politeness in Thibet; the art of the telegrapher would have spelled black magic a few centuries ago. Enough has perhaps been said to give plausibility, at any rate, to the statement that mental processes do not intrinsically mean, that meaning is not a constituent part of their nature; and that may suffice for the present; we shall come back again to meaning later. Value and use need hardly be discussed; they are, far more clearly than meaning, additional to (and detachable from) experience. If, however, the reader thinks that the point should be worked out in their case also, he may put them through the same sort of examination as that to which we have just subjected meaning; evidence will at once be forthcoming.

§ 7. The Scope of Psychology.—Science, like the Elephant’s Child in the story, is full of an insatiable curiosity. Just as the physicist reaches out, analysing and measuring, to the farthest limits of the stellar universe, so does the psychologist seek to explore every nook and corner of the world of mind; nay more, he will follow after a mere suspicion of mind; we have seen him trying to psychologise the plants. The result is a vast number of books and monographs and articles on psychology, written by men and women of very different interests, knowledge and training; for science does not advance on an ordered front, but still depends largely on individual initiative. A high authority on the Middle Ages has said that one mortal life would hardly suffice for the reading of a moderate part of mediÆval Latin; and the psychologist must recognise, whether with pride or with despair, that one life-time is hardly enough for the mastery of even a single limited field of psychology. The student has to get clear on general principles, and then to resign himself to work intensively upon some special aspect of the subject-matter,—keeping as closely as he may in touch with his fellow-workers, and aiming to see his own labours in a just perspective, but realising that psychology as a whole is beyond his individual compass.

Does that sound exaggerated? Let us then attempt a rough classification! We begin with the psychology of the normal mind. Under this heading we have to distinguish (1) human psychology. Human psychology may be general, the psychology of the adult civilised man, which forms the principal topic of the text-books of psychology; special, the psychology of the human mind at some other stage of individual development: infancy, childhood, adolescence, senility; differential, the study of the differences between individual minds; or genetic, the study of the development of mind from childhood to manhood, and its gradual decay in old age. (2) Animal psychology may be subdivided, in the same way, into general, special, differential and genetic psychology. (3) Plant psychology is still in its first beginnings; but many students are taking the subject seriously. (4) Comparative psychology is the comparative study, either of various types of animal mind, or of the minds of plants, animals and man. It, again, may be general, special or genetic.

All these psychologies deal with the individual mind. There is also a collective psychology; and, though its divisions are not yet sharply marked off from one another, we may distinguish (5) social psychology, which includes the study of what is called the social consciousness, and also the scientific study of the products of the collective mind: language, law and custom, myth and religion; (6) ethnic psychology, the differential psychology of nations or races; and (7) class psychology, the differential psychology of classes or professions.

Turn now to the psychology of the abnormal mind. Here we find, under the heading of individual psychology, (8) the psychology of deficient and exceptional minds; of blind deaf-mutism, of genius, of the subnormal and the supernormal child; (9) the psychology of temporary mental derangement; of dream, of hypnosis, of intoxications, of occasional hallucination and illusion; and (10) the psychology of permanent mental disorder, of the chronic derangements of insanity. We may also study (11) the psychology of temporary derangement of the collective mind, that is, of the manias or mental epidemics that sometimes sweep society: the mediÆval dance-manias, unmotived panics, outbursts of superstition, of religious persecution.

If we proceed further, from psychology proper to psychotechnics, or to what is ordinarily termed applied psychology, we have the great departments of (12) educational psychology, (13) medical psychology or psychotherapeutics, (14) juristic psychology, or the psychology of evidence and testimony, and (15) economic psychology, which includes such things as vocational psychology and the psychology of advertising.

You need not ascribe any special importance to this classification; still less need you memorise it. The various topics might very likely be better arranged, and the list is by no means complete. Realise, however, that every term in the list has its text-books and treatises, its manuals and monographs, and very likely its magazine or magazines; realise again that, although the emphasis varies in the different countries, the list might be filled out not alone in English, but in all the chief European tongues; and remember, lastly, that some of the headings have a very long history, and a correspondingly long series of printed works over and above those that represent current knowledge. You then get a glimmering of the range and scope of psychology. It is true, of course, that much of what has been printed is out of date, or inaccurate, or superficial, or prejudiced, and for these or like reasons may safely be scrapped. Yet it all has to be sifted.

The mere bulk of psychological material would be less formidable if every writer adopted the same principles and wrote from the same point of view; but that is hardly to be expected. Psychology has always been exposed to the infection of common sense; it has only recently turned to scientific methods; and when the time came for it to take its place among the sciences, there was naturally difference of opinion regarding the standpoint it should assume, the procedure it should follow, the model it should seek to copy. Where such differences of opinion obtain, the best way to begin your study is to master one system thoroughly; your ideas are thus made consistent and your knowledge receives an orderly arrangement; then, as you read further, you can use this system as a touch-stone whereby to test new ideas and to arrange new knowledge; and if the new ideas seem preferable to the old, or if the old framework breaks down under the new knowledge, you can alter your own system accordingly. If you begin, on the contrary, by studying a number of works abreast, you are liable to become confused. And it is better to be wrong than to be muddled; for truth, as Bacon said, emerges more quickly from error than from confusion.

§ 8. A Personal Word to the Reader.—These introductory sections are not easy. The only way to make them easy would be, as an Irishman might say, to leave the difficult things out; but then you would come to the later chapters, where we study mental phenomena in the concrete, with all sorts of prepossessions and misunderstandings; psychology would be one long difficulty instead of being, as it henceforth ought to be, a bit of straight sailing.

So you must face the initial difficulty and overcome it. Indeed, you must do more than merely understand. The author’s undergraduates who break down in a preliminary examination always explain that they followed the lectures perfectly, and thought they understood the text-book, but that they were somehow unable to put things properly in their own words. The author’s small daughter who comes home with an elaborate example in compound interest explains, in the same manner, that she thoroughly understood the rule when She explained it, but that she can’t now see just how to go to work for herself. It may be that these excuses are not wholly reliable; they bear, at any rate, upon the present point. You must not only understand what you read as you read it; you must exercise your thought upon what you have read; you must be able to explain the paragraphs, in your own words, to others; you must find instances and illustrations for yourself; you must make the substance of the paragraphs a part of your habitual mental furniture; you must note how the old ways of thinking crop up to mislead you, and must correct and criticise the natural man. In a word, just as you practise your way into a language by reading, translating, writing, speaking; or just as you practise your way into algebra by doing exercise after exercise until the rule seems to be part of you and applies itself of its own accord; so must you keep practising your psychology until it becomes instinctive. You will gain some help by answering the appended questions; but after the book has done all that it can for you, the real induction into psychology remains to do for yourself.

Some of the questions are concerned with forms of expression; and you should take these very seriously, since language will be one of your greatest stumbling-blocks. Language is older than science, and has developed under pressure of practical needs. Hence the phrases that come most naturally to your lips may embody a view of the world, or an attitude toward experience, that is totally foreign to the scientific context. If a visitor from Mars heard us all talking about the sunset, what would he think of our knowledge of the heavenly bodies? Yet we cannot escape from language; and if Newton could express his ideas in Latin, we ought to be able to express ours in English. It is a good plan, at the start, to have your technical definitions always at hand, and to try the effect of substituting these definitions for the words that you have been using; if the resulting clumsiness makes sense, you may let your first expressions pass; but if not, you should try again.

You will notice, as you read on in the book, that back references become numerous. Be advised to look these references up! They send you, in every case, to a particular page, so that their finding is easy, and you can refresh your memory without any great loss of time; though, for that matter, it will do no harm to glance over the section in which they occur. If you, on your part, want to refer to some past discussion, consult the index; it has been made fairly full, and is meant to be used.

Questions and Exercises

Many of the books to which you will be referred, now and later, have appeared in numerous editions, library and popular, English and American. The references are made so complete that you will easily find the corresponding passages in editions other than those used by the author.

(1) Discuss the following definitions of science. If you have access to the books, read the passages in which the definitions occur; if not, do the best you can with your present knowledge. Try to see a reason even for the definitions that you cannot accept.

(a) Science is perfected common sense (Huxley). The definition accords with the view of Spencer that science and ordinary knowledge are allied in nature, and that the one is but a perfected and extended form of the other. What is there in the common interests of these two men, or in the period in which they lived, to account for such a definition?

(b) Reduced to its lowest terms, science is the observation of phenomena and the colligation of the results of observation into groups (Hill).

(c) When may any subject be said to enter the scientific stage? I suppose when the facts of it begin to resolve themselves into groups; when phenomena are no longer isolated experiences, but appear in connection and order; when, after certain antecedents, certain consequents are uniformly seen to follow; when facts enough have been collected to furnish a basis for conjectural explanation, and when conjectures have so far ceased to be utterly vague, that it is possible in some degree to foresee the future by the help of them (Froude).

(d) Mechanics is the science of motion; and its problem is to describe the motions that occur in nature completely and in the simplest way (Kirchhoff). Can this definition of mechanics be generalised, so that it applies to science at large?

T. H. Huxley, Science Primers: Introductory, 1880, 18 f.; H. Spencer, The Genesis of Science, in Essays, ii., 1891, 8; A. Hill, Introduction to Science, 1900, 3; J. A. Froude, The Science of History, in Short Studies on Great Subjects, First Series, i., 1901, 13 f.; G. R. Kirchhoff, Vorlesungen Über mathematische Physik: Mechanik, 1883, 1.

(2) Helmholtz tells us that whoever, in the pursuit of science, seeks after immediately practical utility, may generally rest assured that he will seek in vain; and Clifford asserts that the most useful parts of science have been investigated for the sake of truth, and not for their usefulness. Yet Pearson holds that one of the claims of science to our support is the increased comfort that it adds to practical life. How do you reconcile these statements?

H. von Helmholtz, On the Relation of Natural Science to General Science, in Popular Lectures on Scientific Subjects, i., 1904, 25; W. K. Clifford, On Some of the Conditions of Mental Development, in Lectures and Essays, i., 1879, 104; K. Pearson, The Grammar of Science, ch. i., 1900, 29 f., 37.

(3) Discuss the following definitions of psychology:

(a) The science which describes and explains the phenomena of consciousness, as such (Ladd).

(b) The science of behaviour (Pillsbury).

(c) The science of individual experience (Ward).

(d) The positive science of mental process (Stout).

G. T. Ladd, Psychology, Descriptive and Explanatory, 1894, 1; W. B. Pillsbury, The Essentials of Psychology, 1911, 5; J. Ward, Psychology, in EncyclopÆdia Britannica, xxii., 1911, 548; G. F. Stout, Analytic Psychology, i., 1896, 1.

(4) Can you bring the following series of statements into relation, and show that they illustrate natural (even necessary) stages in the history of human thought? (Note the phrasing in every case!)

(a) The savage thinker seems to have taken for granted, as a matter of course, the ordinary operations of his own mind. It hardly occurred to him to think about the machinery of thinking (Tylor).

(b) The modern mind is, what the ancient mind was not, brooding and self-conscious; and its meditative self-consciousness has discovered depths in the human soul which the Greeks and Romans did not dream of, and would not have understood (Mill).

(c) When to save his own soul became man’s first business, he must needs know that soul, must study, must examine it. Prescribed as a duty, introspection became at once a main characteristic of religious life (Burr).

(d) There is nothing more interesting to the ordinary individual than the workings of his own mind. This interest alone would justify the existence of the science [of psychology] (Pillsbury).

(e) If we could say in English ‘it thinks’, as we say ‘it rains’ or ‘it blows’, we should be stating the fact most simply and with the minimum of assumption (James).

E. B. Tylor, Animism, in Primitive Culture, i., 1891, 497; W. Knight, Rectorial Addresses delivered at the University of St. Andrews, 1863-1893; J. S. Mill, 1894, 38; A. R. Burr, Religious Confession and Confessants, 1914, 86; W. B. Pillsbury, op. cit., 5; W. James, The Principles of Psychology, i., 1890, 224 f.

(5) What is the earliest notion of your own mind that you can recall?

(6) Four newspapers describe the same gown as gold brocade, white silk, light mauve, and sea-green with cream or ivory sheen on it. How could this difference of report have arisen?

(7) Newton is said to have discovered the law of gravitation by observing the fall of an apple from a bough. Was this a simple observation, or could it be said to have anything of the experiment about it?

(8) What are the characteristics of a good observer? of a good experimenter?

(9) The older psychologies speak, in technical terms, not of mental processes but of powers, faculties, capacities of the mind. What view of mind do these expressions imply?

(10) Rousseau remarked that definitions would be all very well if we did not use words to make them; les dÉfinitions pourraient Être bonnes si l’on n’employait pas des mots pour les faire (Œuvres complÈtes de J. J. Rousseau: Émile, tome i., 1823, livre ii., 160). Illustrate this remark by reference to psychology.

(11) Try to describe your experience on some occasion which leads you to say: (a) I have made up my mind; (b) I have half a mind to do so-and-so; (c) That puts me in mind of so-and-so. Try to get down to the bare facts; it will be difficult; but try again and again, and do not be satisfied to report meanings.

(12) Describe your fountain-pen from the points of view of common sense, of physics, and of psychology. Do not attempt too much detail, but get the differences in point of view clearly on paper.

References for Further Reading

§ 1. Some general references have already been given; add W. Whewell, History of the Inductive Sciences, 3d ed., 1857. The book is out of date, but still useful. For science in the Middle Ages, see H. O. Taylor, The MediÆval Mind, 2d ed., 1914 (references in index). For the genesis of science, consult Tylor, as cited above; J. G. Frazer, Balder the Beautiful, 1913, 304 ff.; all the volumes of The Golden Bough are instructive. For an object-lesson in scientific thinking take H. Spencer, The Study of Sociology, 9th ed., 1880 (also no. 5 of International Scientific Series).

§ 2. Tylor, as above; J. G. Frazer, Taboo and the Perils of the Soul, 1911, 26 ff.; E. B. Titchener, Psychology: Science or Technology? in Popular Science Monthly, lxxxiv., 1914, 39 ff.; J. Ward, Psychology, in EncyclopÆdia Britannica, xxii., 1911, 547 f.

§ 3. W. McDougall, Physiological Psychology, 1905; W. Wundt, Principles of Physiological Psychology, i., 1904, 1 ff., 27 ff., 280 ff.; R. M. Yerkes, Animal Psychology and Criteria of the Psychic, in Journal of Philosophy, Psychology, and Scientific Methods, ii., 1905, 141 ff.; M. F. Washburn, The Animal Mind, 1908; A. W. Yerkes, Mind in Plants, in The Atlantic Monthly, Novr. 1914, 634 ff.; J. B. Watson, Behaviour, An Introduction to Comparative Psychology, 1914.

§ 4. O. Kuelpe, Introduction to Philosophy, 1897, 55 ff.; Wundt, as above; G. T. Ladd and R. S. Woodworth, Elements of Physiological Psychology, 1911; E. W. Fiske, An Elementary Study of the Brain, 1913; K. Dunlap, An Outline of Psychobiology, 1914.

§ 5. W. S. Jevons, The Principles of Science, 1900, bk. iv., chs. xviii., xix.; E. B. Titchener, Prolegomena to a Study of Introspection, in American Journal of Psychology, xxiii., 1912, 427 ff.; O. Kuelpe, Outlines of Psychology, 1909, § 2; W. A. Hammond, Aristotle’s Psychology, 1902; C. A. F. Rhys Davids, A Buddhist Manual of Psychological Ethics, 1900.

§ 6. M. Howe and F. H. Hall, Laura Bridgman, 1903, 49 f.; G. Stoerring, Mental Pathology in its Relation to Normal Psychology, 1907 (the quotations from this work are sometimes condensed in the text); S. I. Franz, Handbook of Mental Examination Methods, 1912, 68, 80.

§ 7. Add, as typical, to works already cited: W. Preyer, The Mind of the Child, 1888-9 (human special); J. M. Baldwin, Mental Development in the Child and the Race, 1906 (human genetic); id., Social and Ethical Interpretations in Mental Development, 1906 (social); G. Le Bon, The Psychology of Peoples, 1898 (ethnic); A. Moll, Hypnotism, 1891 (derangement); G. Le Bon, The Crowd, 1910; J. Jastrow, Fact and Fable in Psychology, 1900 (collective derangement); E. L. Thorndike, The Principles of Teaching Based on Psychology, 1906; H. MÜnsterberg, Psychology, General and Applied, 1914. For the history of psychology, see O. Klemm, A History of Psychology, 1914; M. Dessoir, Outlines of the History of Psychology, 1912.