Psychology, General and Applied
Chapter 16: Individual Differences
Hugo Münsterberg
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The Aim of Social Psychology.—If the psychologist tries to describe and to explain all the mental phenomena he cannot disregard those which result from the coöperation of several individuals. The social group may be as small as a family or as large as the concert of civilized nations. It may be as fugitive as the chance meeting of two strangers one of whom asks a question and the other replies. or as stable as a life partnership in marriage. It may be held together by social or professional, economic or political interests. It may embrace people in the same room who see and hear one another ; it may be formed by individuals scattered over the world, who know one another by work or reputation. It may be an involuntary relationship like that of the members of a crowd in a panic, or a definitely regulated combination on the basis of statutes and contracts, programs and platforms.
Whatever the form of the social group may be, new mental functions arise from the mutual influence of its members. We have no phenomenon of social psychology before us, if two or a million persons are performing the same act, perhaps perceiving the moon, without being influenced by one another. The interest of the social psychologist begins only where they enter into actual relations : the individual experiences mental states which would
( 225) not enter his consciousness without the existence of other men. The simplest gesture or imitation as well as the most complex act controlled by custom or fashion or by law, involves such consciousness of the social group. The psychologist must trace both the mental contents which result and the psychophysical processes which lead to them. Every process in society in which the minds of several individuals coöperate thus becomes proper material for psychological analysis.
On the surface these psychological efforts seem to coincide with those of the sociologists. The science of sociology can be interpreted in many ways, and the differences of definitions point to a real variety of tasks. Some students of sociology consider it their goal to describe and to explain every life function of society. Others claim that this would make all the social sciences, including economics and politics and history only parts of sociology. They want to concentrate the interest of the sociologists on the particular question of how society is formed and how this combination and coöperation of men have developed. But whatever the wider or narrower view of the sociological problems may be, they are characteristically different from the interest of the social psychologist. For the sociologist the starting point is the group itself. Its structure, its .life, its achievement, are studied, and the mental functions which enter are only means for the explanation of the group development. For the social psychologist these mental functions are the real objects. He cannot start, therefore, from the group as such, but must always begin with the individuals. The state or the family, the party or the crowd, the club or the race, has no selfobserving consciousness of its own. The psychological experience of the group goes on in the individual members who stand in contact with one another. Social psychology is therefore the greatest help for sociology, but it remains an independent science.
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On the other hand, the social psychologist who starts from the processes in the individual personalities must finally advance from these members of society to their unified organization. He has a full right from his psychological standpoint also to speak of the mind of the nation or of the mob or of the family. He does not refer by that ton mystical higher personality which exists somewhere above the individuals. He forms such a conception in analogy with the coöperation of the cells in the brain. Millions of neurons coöperate in every brain. Each such neuron has its centripetal, its central and its centrifugal part, and each may have its elementary psychical accompaniment. Any number of them may work together in a group, and all together form the personality. In this way every person has its centripetal, its central and its centrifugal part, and its functioning is accompanied by mental states, and any number of such persons may coöperate, too, in groups, and their totality forms the life of mankind. The whole psychophysical brain is as real as each of its cells : in this sense we may say that the whole social group is as real a psychophysical unit as any individual person.
The study of social psychology shows so far a tendency through which its sphere becomes narrower than seems justified. Too often the idea prevails that the interest of the social psychologist properly lies only where the individuals are parts of a general mass, but that it is out of place where single personalities are in the foreground and dominant. The processes of language, of customs, of faiths, in short all which the undifferentiated group produces, are inclosed in the circle, while the productions into which individual statesmen or scientists or artists or religious leaders enter with their personal originality are excluded from the analysis of social psychology. The chief illustrations are therefore taken from the life of the primitive peoples, because the social consciousness of the savages
( 227) seems less differentiated, while the highly civilized life is clearly guided by masterful individuals. But that is just as narrow as if we were to omit in individual psychology those states in which a particular idea or feeling or decision becomes prominent in consciousness. We know that in the individual mind the attention usually focuses on one mental content, but this remains nevertheless in complete interplay with all the other elements of the mind. In the social consciousness of the group, too, the attention may be focused on a particular part ; on the intellectual or artistic or religious or political or industrial leader. But the mutual influence between him and his followers or his opponents lies entirely within the compass of social psychology. The highest development of the civilized nations is material for psychology as much as the vague, unshaded existence of the primitive races.
Childhood and Maturity.—Where individual psychology ends social psychology has to begin. The personality is the highest unit which is reached in the former : a combination of at least two personalities is the smallest unit which can be object for the latter. But before we may ask how personalities can influence one another and work together and experience mental states which they could not have by themselves, we must evidently consider how far the individuals differ from one another. No relation between men can be fully characterized, if we disregard the personal variations. When we studied the elementary processes in individual psychology, we began with the stimulations, because they furnish us the elements, the sensations. Only after knowing these manifold sensations could we proceed to the further elementary process, to the association. Before we ask how individuals associate, we must know, too, how they differ from one another. No two individuals are alike. If men were mentally alike, the social groups would have an entirely different character.
Here we have to enumerate, of course, only those dif-
( 228) -ferences which have significance for the social organization and the resulting social mental states. We may classify them in four groups. The individuals who form the social world differ, first of all, in age. The age variations evidently forth it class of their own on account of their necessarily pasting character. The group which children and parents or pupils and teachers form is perfectly controlled by the mental characteristics of youth in contrast to the elders. The second class may embrace all the differences which are common to whole groups of individuals, for instance to all women as against men, or to all members of a race, or to still individuals of a special nation, to all members of a profession or of a vocation. The third class contains the individual differences in the narrower sense of the word, that is, the differences in which we cannot recognise the traits of a large group such as sex or race, but in which the individual really differs from his neighbor. Here belong the variations of temperament, of character, of intelligence, of talent and so on. Finally we may class together those individual variations which interfere with the normal harmony of mental life, the pathological mental states.
We have sometimes before had occasion to point to the mental life of the child. Every single psychical function which we analyzed in man can be traced backward .to a definite period in the child's development, where it slowly began to be formed. Selfconsciousness and will and emotion and ideas and attention are not born with the infant, but slowly secured. Yet we have seen that the newborn child does start with a wonderful equipment of nerve connections which produce important, useful reactions in response to the stimulation of the outer world. This reaction apparatus is in no way perfected by nature in the first days of life. New anatomical brain paths grow and become efficient during the child's development, but the reactions are from the start adjusted to the simple
( 229) needs of the infant, and everything which follows is only growth and differentiation.
Even the senses which are open to stimuli furnish at first scanty material. The child does not see colors during his first year ; the optical impressions are only shades of gray and movements. The most significant difference, however, is not the meagerness of sensation material, but the lack of connection. Every impression stands by itself on the background of vague organic sensations and feelings. It is one blurring content of consciousness without any inner organization. Slowly memory images begin to arise,' and emotions shade the behavior. With the third year not only the memories but general ideas and complex affections are acquired. The learning of the language hastens the intellectual development; the indefatigable method of trying and trying again trains all the psychomotor powers, and they in turn influence the intellectual differentiation and the emotional state.
The compass of experiences is still small, the judgment untrained, but the child of five years has gained all the mental traits of the adult. Yet every function needs its further development. The voluntary attention is still very easily exhausted and lacks all perseverance; the memory is still untrained and highly deceptive ; the power of inhibition very undeveloped; the time sense and the number sense clumsy and crude ; the apperception controlled by superficial analogies. But every day brings progress, first of all through the child's own efforts, through his exploring in the world and assimilating from the world mentally that upon which he is ready to react. The stream of knowledge becomes broader and broader; the motor training becomes more differentiated ; the intellectual abilities become serviceable to tasks of increasing difficulty; and with the power of reading the mental surrounding is endlessly enlarged.
Yet the years of later childhood, of youth and adoles-
( 230) -cence are not merely an unfolding in which every function becomes more efficient; they are at the same time a development with marked rhythms and with changes characteristic of definite periods, changes which may involve a decrease in the activity of certain mental functions as well as an increase in that of others. The play of the imagination is most vivid in childhood, as it is less checked by an objective memory. The impulsiveness of the child becomes repressed by the sober purposiveness of the adolescent; the quickly growing interest in social relations must inhibit many it fully developed childish interest. The predominant feature of the period of puberty is the rich development of high-pitched feelings and sentiments, often with quick changes and deep influences on the whole intellectual and active life.
The time from the twentieth to the sixtieth year is the period in which the energies reach their full differentiation. The first half of this period may be characterized by the greatest elasticity which the individual. can attain ; the second half by the greatest maturity of judgment. Mit while the intellectual powers may continue to increase with experience, the feelings become duller, the motor impulses less energetic and the mental traits of old age begin to creep into the psychophysical behavior. The associative mechanism weakens, the spontaneity of the mind decreases, the senses suffer, the memory for recent impressions becomes defective, the mental life decays. The rhythm of this life history differs greatly with different individuals. Precocious children race through the stages of childhood; many vigorous men reach fourscore years without marked symptoms of decay. But these differences of individual rhythm belong together with those of talent or temperament. Here we have to deal with the average structure which allows a rather precise mental picture of the infant of two, or of the child of eight, or of the adolescent of sixteen, or of the old man of eighty.
( 231) Sex and Race.—If we are to trace the characteristic mental features of an individual, we may be greatly aided by knowing to which human groups he belongs. Without analyzing his mental physiognomy we popularly take it for granted that an Italian has different mental tendencies and dispositions from an Esquimaux, a fisherman from a scholar, ai jockey from a minister. In short, the mere fact that a man belongs to an objective group, to a race, to a people, to a vocation, seems to allow the assumption that certain mental qualities are to be expected. In scientific thinking we have before us the problem of group psychology. Its specific question is how far certain traits are common to all members of an objective group. How far have all the Chinese something in common which makes them different from all the Japanese? How far have all the working men in factories, or all soldiers, or all mountain dwellers, common mental features? It is evident that the groups which are analyzed in such a survey by no means embrace only individuals who are in actual contact with one another, or who have any mutual influence. The mountain dwellers of the whole globe are without connections; those of South America do not come in contact with those of Asia. They form, accordingly, no social group in the sense of social psychology, but they do form a group in the sense of group psychology, as we can ask whether there is anything common to all of them. In. the same way we may treat all epileptics or all violinists or all chess players or all people with brown eyes as groups whose common features may be studied. Wherever we have an objective trait which allows a definite grouping, it may be worth while to examine whether certain mental features are correlated with it.
Of course such a correlation will hardly ever be complete. We may find that one race is phlegmatic and another vivacious, but that certainly does not exclude their sometimes exchanging rôles. If we have a large number
( 232) of individuals, the average characteristic may be relied on. A whole crowd of Russians will behave differently from a crowd of Spaniards Is or from a crowd of Englishmen, but the individual Englishman may show traits which we are accustomed to expect from a Spaniard or a Russian. A man of affairs may have the artistic temperament of a musician, and a musician may have the practical mental trend of a explain of industry. There are men who have a female trend of mind, and women with strikingly male mental features. That an individual belongs to a certain group, therefore, does not mean that he is invested with all the average features of the group. But this does not negate the value of psychological group analysis.
The two largest groups which may be contrasted are those of male and of female individuals. Careful experiments have thrown light on the differences of memory, attention, feeling and other mental functions in boys and girls and in mature men and women. Such experimental results can easily be supplemented by social, statistical material, by historical reports and the account of male and female achievements in civilization. The psychologist certainly cannot point to any one mental function which is present in all men and absent in all women, or vice versa. It cannot even be said that either sex possesses a characteristic trait in which some members of the other sex may not excel too. Yet such studies leave no doubt that significant differences exist. It would be superficial to claim that the mind of man or of woman is superior, but each has its peculiar points of strength and weakness. The survey of a large field shows first of all that men vary more strongly. Women are nearer to the average type. The extreme variations above and below the average occur more frequently with men. They show the greatest development of intellectual, emotional and volitional powers in the case of scientific or artistic or political or religious genius and the greatest criminal depravity. The average
( 233) female mind is patient, loyal, reliable, economic, skillful, full of sympathy and full of imagination; on the other hand it is capricious, oversuggestible, often inclined to exaggeration, disinclined to abstract thought, unfit for mathematical reasoning, impulsive, overemotional. The good and bad features alike can be understood as the results of a more emotional temperament in women than in men, and secondarily as the results of greater activity. But the chief point is that in men the various contents of consciousness remain separate, while in the mind of women they fuse. Her life, therefore, has more inner unity, and she shows more readiness to devote all mental energies to one idea. But for the same reason she must be influenced by prejudices, must show a lack of logical discrimination, must be under the control of the present impressions and too little directed by the arguments which reason and memory supply.
The mental traits of the different races and peoples are much discussed in ethnological studies, but have as yet been very little examined by the methods of scientific psychology. Those mental functions which can most easily be submitted to experimental investigation, the elementary functions of perception, attention, memory, and feeling show rather insignificant differences. The visual sensations or the reaction times or the memory span are the same for an American and a German and a Russian. The real variations appear only in the more complex functions which are less accessible to mass experiments. Hence the material of ethnological psychology still lacks experimental exactitude. It is taken partly from a general observation of the peoples and their life and partly from a psychological interpretation of their objective achievements in the world of civilization. The manifoldness of traits becomes truly psychological material as soon as the particular forms of behavior and of achievement are recognized as the expressions of simple mental functions.
( 234) It has been pointed out, for instance, that in Europe there must be a fundamental racial difference between the Greco-Latins and the Teutons. The Greeks, Romans, Italians, Spaniards, are talkative, quick and vivacious in their actions, while the Germans, English, Dutch, Scandinavians, are taciturn and deliberative. The Greek temples are simple; the northern cathedrals complex. In music the Latin nations love the single melody in its clearness and simplicity; the Teutonic nations the complexity of counterpoint: in literature the unity of action in Greek or classic French draina contrasts with the complexity and wealth of Shakespeare or Goethe: in painting the simplicity of Italian art is strikingly different from the manifoldness of the Dutch. But the same contrast appears in the intellectual and emotional, in the political and practical life. The southern peoples are children of the moment: the Teutonic live in the things which lie beyond the world, in the infinite and the ineffable. Even in the popular games the Greeks confined themselves to the simple contests like running and jumping and throwing the discus, while the Teutons prefer the complicated cricket and football. In short, the Greco-Latin civilization tends toward clearness and simplicity; the Teutonic toward complexity which is based either on a greater number of factors or on a greater irregularity in their combination. If it is brought to its ultimate psychological expression, the Greco-Latin is absorbed by what the perception offers, and his attention inhibits the onrushing associations; the Teutonic mind divides its attention and always has room for suggested side issues. A social group into which a large number of Italians or Frenchmen enter must therefore have mental features sharply different from those of a social combination in which Englishmen or Germans prevail.
Much psychological attention has been devoted to the primitive races, and recent ethnological expeditions have
( 235) not seldom been accompanied by psychologists who curried their reaction time instruments and attention apparatus to the South Sea Islands. Yet the results indicate a very thorough similarity of all human beings, as far as the most elementary functions are concerned. The popular idea, for instance, that the senses of the savages are sharper than those of civilized men can be disproved by exact experiment. If certain tribes are able to recognize objects at distances at which civilized men do not notice anything, it is essentially through training of the attention for the observation of small signs, a training which is forced on them by the conditions of their life. The true mental differences between the primitive and the civilized peoples appear in the more complex functions. Sociologists are inclined to insist that the power of attention in primitive man, the power of inhibiting impulses and the power of original thought are weaker than in the higher races. But these impressions are too often gained by studying the mind's work through tests which do not belong to the natural course of primitive life. If the standpoint of the primitive man himself is really taken, these mental powers, in particular the power of inhibiting impulses, frequently seem remarkable.
Character and Temperament.—As soon as we turn to groups of vocational character, the situation shows new features. In our highly differentiated social life the mental traits of different professional groups seem even more distinct than those of different racial elements. In America a hundred lawyers, a hundred actors, a hundred school teachers, a hundred storekeepers and a hundred ministers would show in the group average stronger difference of mental behavior than the average of equally large groups of Anglo-Americans, Swedish-Americans, German-Americans and Scotch-Americans. But those racial groups are formed by birth, the vocational groups by free selection, and this selection is evidently itself a mental process. If we ask
( 236) for the mental traits of the actors as against the ministers, we contrast two groups which are originally characterized not by the external performance on the stage and in the pulpit, but by the internal desire for theatrical life or for church life. These desires are mental functions and the real problem is then : what are the other mental traits which usually accompany these desires? The problem of group psychology is then replaced by the other problem: how far do various mental traits hang together? But if we raise this question, we must ask first how far mental traits vary from individual to individual.
We must now consider the most prolific source of individual differences, the personality as the product of its inherited dispositions. In any group, in any race or community or vocation, we find psychical differences from person to person, just as in spite of racial anthropological traits even in the same city no two faces look exactly alike. Individuals may vary in their emotional dispositions or in their tendencies to action or in their ability for mental readjustment or in their fitness for particular achievements: the differences of temperament, of character, of intelligence and of talent. But these marked variations to which we are accustomed to give our chief attention in practical life are surrounded by innumerable differences of perception, memory, imagination, attention, feeling and volition. We frequently had to point to such different shadings before. We spoke of the visual, acoustical and kinesthetic type of reproduction and of similar mental variations.
The individual traits are to a certain degree the results of life history. They have developed through the experiences in childhood, through the training of abilities, through the acquiring of associative material, through the awaking of desires and interests in the formative period of the mind. But no training and no external influence can entirely supersede the inborn tendencies. They are
( 237) the product of inheritance. Not only unusual talents like the musical or mathematical or linguistic powers can be traced through family histories, but the subtlest shades of temperament, character and intelligence can often be recognized as an ancestral gift. Statistical studies which covered many characteristic opposites like industrious and lazy, emotional and cool, resolute and undecided, gay and depressed, fickle and constant, cautious and reckless, brilliant and stupid, independent and imitative, loquacious and silent, greedy and lavish, egoistic and altruistic, and so on, have indicated clearly the influence of inheritance on every such mental trait. The inheritance from father to son and from mother to daughter is thirty to forty per cent. more frequent than the crossed inheritance from father to daughter or from mother to son. But the influence of the mother on the mental traits of the children is about ten per cent. stronger than that from the father. The probability that intellectual qualities will be inherited in the second generation is greatest, next the moral qualities and after them those of temperament.
The varieties of temperament have always been noticed. The old division into the melancholic, phlegmatic, choleric and sanguine persons drew its names from a long forgotten medical theory, but it refers to types of emotional life which can still be contrasted today. The sanguine and the phlegmatic are inclined to superficial emotions and their superficiality makes both somewhat optimistic, but, while the sanguine person experiences the emotions in quick rhythm, the phlegmatic passes slowly through the changes of feeling. The choleric and the melancholic are subject to strong emotions, on the whole, with a pessimistic tendency, but with the difference that the choleric has the quick, vivid, almost stormy emotions, the melancholic the slow, lasting excitements and depressions. But while these four groups of dispositions only are usually called temperaments, we can easily discriminate other lasting ten-
( 238) -dencies in affective life. The contrast of frivolous and of morose, of courageous and of timid, of passionate and of apathetic dispositions do not coincide exactly with any temperament.
The disposition to will action, the character, varies especially in its strength, The power to keep the selected motive dominant can grow to a heroic force against which no fear and no temptation can prevail to change the psycho-motor setting, and it can sink down to the attitude of the weakling whose will decisions are outbalanced by any new chance proposition or by any passing fancy. But the powerful character can serve egoistic as well as altruistic ends; thus the mere strength is no pledge of morality. The morality, the frankness, the loyalty, the reliability of character and their opposites are hardly elementary dispositions, but combinations of will and emotion.
Still richer are the differences of imagination, even if we abstract from theme varieties of sensorial reproduction which make one man's imagination work in pictures and another's in tones, one in words and one in movements. The fundamental differences of imagination lie in the power to organize the associative material under the control of subjective feelings and wishes. This difference between poor and rich imagination may be divided further by the individual tendency to yield passively to the play of ideas or to control them actively in the service of a plan, however much this plan may be condensed in the mind into a mere emotional excitement. The artistic imagination is of this active type.
Intelligence.—By intelligence we meant the ability to adjust the mental setting to a new situation. No teacher who knows the class has any difficulty in grading the pupils according to their intelligence. Such ranking would not correspond to the total intellectual achievement of the pupils, as the intelligent one may be lazy and careless and the rather stupid may overcome his defect in the
( 239) school class by industry and effort. The intelligent may even be hampered by a poor memory and the less intelligent helped by an excellent memory, and yet independent of these secondary aids to intellectual work the poor intelligence remains easily recognizable. No one's intelligence can serve equally well in all departments of intellectual culture. Disposition and training makes one more able to show his intelligence in pure reasoning and quick adjustment to abstract judgments, while another may prove it in rapid adaptation to complex practical conditions. One may more quickly turn to superordinated ideas and another to subordinated ones, one may be more inventive, another more speculative.
In the psychological laboratories methods have been developed not only to study all such variations by long research, but to determine them quickly by standardized test experiments. It is not difficult to find out the quality of an individual's memory for numbers or words or colors or faces or tones or whether his attention has a wide or a narrow span, whether it is steady or fluctuating, whether the associations are controlled more by recency or by frequency or by vividness, whether they are slow or quick, whether they are chiefly coördinated or subordinated, and so on without end. But from such simple tests the analysis may proceed to more complex experimental questions by which the temperament, to a certain degree the character, the tendency to emotion, and above all the variations of intelligence can be traced. The experiment creates miniature situations in which the individual has to perform his act and this can be compared with average achievements under the same conditions.
We may test the intelligence by measuring the time needed to recognize certain wrong conclusions as illogical, or to fill out certain blanks in a sentence, or to make a sentence out of certain given words or a word out of given letters or to solve an elementary technical problem such as
( 240) the opening of a box with a complex system of fastenings. This study of mental tests, which has almost grown into a science by itself, plays its most significant role in the service of practical achievement. Such tests are needed to determine for what function in life a man is best equipped, or how far the testimony of a witness in court is reliable, or what defects of mental life can be found in a patient, or what degree of Intelligence can be accredited to a pupil. In short, the problem of tests is so firmly connected with the work of applied psychology that it had better be left for our psychotechnical part.
The test experiment leads also to the difficult question of how far variations in different mental functions are correlated. Is it true that a particular kind of memory goes with a particular kind of attention? Does strong character coincide with high intelligence? Is a rich imagination connected with a special temperament? Is it true that mathematical and musical talent occur together? Does a good memory for figures accompany a good memory for forms? Practical life gives plenty of hints in such correlation problems, and the proficiency of the pupils in school in the various fields of knowledge offer rich material for such comparative studies. But the chief supply of data must come again from the experiment. We may test the memory of a hundred men by measuring the number of seconds necessary to learn certain figures or words; the rapidity of reaction by measuring in thousandths of a second the response to an optical stimulus; the power of discrimination by measuring the just perceivable differences of pitch, of color and of weight ; the attention by measuring the number of c's and is which can be crossed out on a printed page in five minutes; and so on. For each of these tests we may rank our hundred subjects according to their achievement, and then study how far the order corresponds. With exact formulae we can deduce
( 241) from such results how far proficiency in one task corresponds to proficiency in another.
But here too the practical interest prevails. We want to foresee through the study of such correlations what we may expect from an individual who shows a particular trait. In the interest of practical purposes we want to predict whether he possesses certain other traits too. The central theoretical fact is that such a correlation does not exist between mental functions which have no common element or no common cause. The degree of correlation simply indicates the relation between those conditions which the two functions have in common and those which they have not in common. This whole science of correlation throws a new interesting light on the inexhaustible manifoldness of human individuality and emphasizes anew how different the individuals are who enter into the social groups.
Abnormal Variations.—The individual differences of man are not completely characterized, unless the variations are also considered by which the mental equilibrium is disturbed : the abnormal variations. We have repeatedly had to discuss the changes which disease may bring; we traced the losses of memory or the splitting of the personality and so on. One thing showed itself at every point : the mental disease does not introduce psychological elements or functions which are different from those of normal life. Every pathological variation consists of the same psychophysical processes which we know from ordinary behavior. What is changed is only the proportion of the processes. Their harmony is disturbed; we compared it with a caricature in which the normal relation of the features is distorted. The cartoon shows too much or too little of some bodily trait. In the distorted mental physiognomy there may be too much or too little of an emotion or of a volition or of an idea or of attention, too strong or too weak reactions or associations or inhibitions.
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This comparative interest in the pathological trait as a mere extreme variation of the normal is indeed essential for the theoretical psychologist, in contrast to the interests of the physician, who must look on those mental disturbances as symptoms of definite diseases. If we approach in applied psychology the problems of psychotherapy, this interest of the physician must be decisive. But here in the Held of theoretical psychology we are not concerned with symptoms of diseases. We have only mental variations any one of which may enter into many diseases, just as fever may be a symptom of many bodily disturbances. Above till, each of these pathological variations appears to the psychologist in a continuous series which leads from the normal to the pathological without any sharp demarcation line.
The extreme depression of the melancholic patient is then only an abnormally strong increase of a normal sadness, and the gaiety of the maniac an exaggeration of a normal hilarity. We know less intense fluctuations in the compass of normal life; we know pessimists who are easily depressed, and silly persons who are often hilarious without reason. It is the same variation, but we call it normal, as long as the personality still retains its equilibrium: we call it abnormal, as soon its this balance of the mental functions becomes so disturbed by the exaggeration of the emotion that the ordinary life purposes cannot be fulfilled. The maniac who is so excited that he gives no attention to the outer world or the melancholic patient who in his brooding declines to cat, cannot survive in the struggle for existence. If the mental mechanism as a whole secures a checking of a too strong or a substitution for a too weak development, the personality may be unusual, eccentric, or somehow deficient, but not pathological. The philosopher may doubt the reality of the outer world, but his doubt is completely organized in his mental setting and in no way interferes with his practical attitudes to-
( 242) -ward the world. He is therefore normal, however mach his ideas may differ from those of the average man. But the same doubt as the starting point for behavior which tries to ignore the perception of the outer world is selfdestructive and must lead to the doors of the asylum.
We may discriminate four large groups of mental disturbances with reference to four classes of psychophysical conditions. Large areas of brain neurons may Abe destroyed beyond repair and definitely eliminated from cooperation. The degeneration of extensive brain parts in general paresis is typical of such partial death of the psychophysical organ : mental life crumbles. In a second group the brain neurons are temporarily affected. They may be exhausted, poisoned, paralyzed for a period, but can recover; the partial loss of mental functions may be overcome. The cause of this passing injury is an autointoxication of the body. The special sources of these selfproduced poisons are still little known, but it is certain that the normal working of the brain depends upon the presence of chemical substances in the blood which are supplied by ductless glands. If through a disease of these glands, or through any other disturbance in the metabolism of the body, necessary chemical elements are lacking or are too abundant, the brain passes through longer or shorter attacks of abnormal functioning. The periodic and alternating insanity, the manic depressive attacks, many delusional states, must probably be grouped in this class. As soon as the toxic disturbance is removed, the, poisoning substances eliminated, the brain returns to its normal work. Quite similar is the third group in which the poison is introduced from without. Even a simple alcoholic elation is such a poisoning of the brain, which in its extreme form leads to delirium. Morphinism and cocainism are of the same order.
Quite different from these three groups, and psychologically the most interesting, is the fourth group. It is no
( 244) less based on abnormal changes in the physiological mechanism, but the disturbance is not one by which particularneurons are destroyed or temporarily paralyzed. It is essentially one of abnormal connections in the central brain paths. The excitment irradiates into wrong neuron groups; the association process does not stir up the biologically useful centers. Misleading connections are formed. It is as if the wires were crossed, and a torturing disorder may result. This develops especially from emotional shocks, but may arise in any brain which has a disposition to neuranthenis, or psychasthenic or hysteric states. The after-excitement of certain neuron groups forces the opening of association and reaction paths by which unfitting ideas, movements and gland activities are produced, and by which negatively the normal associations and reactions are cut off. A general dissociation may arise in thin way. Some complex aftereffect of an earlier experience may get increasing control of the psychophysical reactions and work as a foreign intrusion in the mind. The resulting phenomena are of bewildering manifoldness, and it is often very difficult to discover the source of the obsessions, the unfounded emotions, the fears and anxieties, the onrushing movements and all the other erratic functions.
It is this group of abnormal psychophysical processes which has most often suggested the interpretation by subconscious mental states. If this psychical terminology is used only in order to have a convenient means of description, there is indeed no objection. It is easier to describe the aftereffect of an earlier experience and of an emotional excitement as a subconscious memory with subconscious affections than to characterize the afterprocess in terms of physiological neuron processes. For the practical purposes of the physician the account of the events as subconscious is almost unavoidable, but on the basis of theoretical psychology, we have no right to surrender the prin-
( 245) -ciples upon which the possibility of psychology depends. We must translate the story of the subconscious mind into t be language of brain physiology.
Destroyed neurons, temporarily paralyzed neurons and wrongly connected neurons are responsible for those extreme variations of mental life in which the individual is partly unfit to enter into the coöperation of the social group. Many gradations between the entirely normal and the strictly pathological are possible; and so we find a dense population in that great borderland region between mental health and illness. The defects of temperament, character and intelligence may show millions of shades, down to the hopeless inefficiency of the imbecile and the idiot whose mind does not grow beyond the development of the child. The stupid, the clumsy, the inattentive, the forgetful, the weak, the morose, the intemperate, the vicious, the cruel, must be dragged down in the struggle for existence by their shortcomings in the intellectual; moral or practical equipment. Yet while their whole life trend may be deeply influenced by such a deficiency, the disastrous effect is the outcome of an elementary variation in the psychophysical system. The association paths do not conduct the excitement easily enough, or the motor settings are not firm enough to resist the opposite impulse, or the inhibitory mechanism is deficient, or the aftereffects of previous stimuli too easily fade away, or the connections for coöperation of the brain parts and for irradiation are in poor working order. In every case the simple cause must produce its effect again and again, and the cumulation of the ill-adjusted responses ruins the social development of the personality. No one is born a criminal, but if his psychophysical equipment is inferior, the chances are great that the temptations of life will find him unprepared for the needed resistance.
