The central aim of the psychologist must be to explain the mental facts. It is not sufficient to describe the procession of mental experiences in us, we must understand the causes which determine that now this and now that appears and disappears, and appears just in this combination of elements. The astronomer is not satisfied with describing the stars, he wants to explain their movements and to determine which movements are to be expected. The psychologist, like the naturalist, aims towards explanation, and it is this demand which forces him to look from the psychical facts to the physical ones, from the mind to the brain. He is under an illusion if he fancies that he can explain mental facts by themselves. The purposive mind has its connection in itself, the causal psychological mind demands for its connection the body. To understand this necessity is the first step towards understanding the relation of mind and brain.

The psychologist's problem of explanation is in one way entirely different from that of the physicist. The physicist finds a world of an unlimited number of atoms which are ultimately conceived as all alike, but each one in a different place, and all the changes in the universe, the movements of the stars, the waves of the ocean, are to be explained by the causal connections of the movements of these atoms. The psychologist, on the other hand, finds an endless manifoldness of elements which are not in space, and which have no space form whatever. My will is neither triangular nor oval; my emotion is neither shorter than five feet nor longer; my memory image of a melody has no thickness and no tallness; my contents of consciousness are as such not in space; their elements cannot pass through any space movements like the atoms of the physicist. Instead of it, the psychical atoms, the sensations, have different qualities, are blue and green, and cold and warm, and sweet and sour, and toothache and headache. The changes which go on in such a system are thus not changes of position and movements, but changes in kind and strength and vividness and fusion; and exactly such changes are the processes which the psychologist wants to explain. He wants to make us understand why this idea grows up and the other fades away, why this impression stands out with clearness as an attended object while the other lacks vividness and disappears, why this volition grows out of that emotion, why this feeling leads to this imaginative thought.

The first step towards such explanation is, of course, in psychology, as in all other sciences, the careful observation of regularities. It quickly leads us to formulate some general laws. Psychology has known, for instance, for two thousand years, that if we have perceived two things together, and later we see the one again, the new perception brings us a memory image of the other thing. If we saw a man's face and heard at the same time his name, seeing his face may later awaken in us the memory of his name, or the hearing of his name may later awaken in us a reproduced memory image of his face. On such a basis, for instance, we formulate some general laws of association of ideas, and as soon as we have such laws laid down, we consider the appearance of such a memory image by association as sufficiently explained. We feel that it gives us sufficient basis to predict that in the future this idea will stir up in us the other idea. Psychology has formulated plenty of such general statements, and they serve well for a first orientation.

Yet can this ever be considered as a last word of scientific explanation of psychical facts? Can psychology really in this way reach an ideal similar to that of scientific astronomy or chemistry? Would the scientist of nature ever be satisfied with this kind of explanation, which is nothing but generalization of certain sequences? Does not the explanation of the naturalist contain an entirely different element? He does not merely want to say that this effect has sometimes been observed and that there is thus probability that it will come again, when similar causes are given. No, the physicist wants to understand those connections of cause and effect as necessary ones. He tries to find sequences which cannot be otherwise because they cannot be thought in any other way. Therefore he is not satisfied with complex regularities, but analyzes them until he can bring them down to simple physical connections, and these physical connections finally to mechanical processes, which realize for us logical necessities. That matter lasts and cannot disappear is such a presupposition, which comes to us with the necessity of logical thinking. We simply cannot think it otherwise. And the whole idea of natural science is to conceive the physical universe in such a way that all changes in the outer world can be understood as the movements of its parts in accordance with such necessary physical axioms. If we knew all the atoms of the present status of the universe, and we knew every present movement of every atom, we should be able to foresee the position of every atom in the next moment and in the following moment and in all following moments, and all that by the necessary continuation of the substance and its energies. That alone is the background of all special physical inquiry, and we rely on the special laws of physics and chemistry, because we trust that this universe, as a whole, could be ultimately understood as such a system of necessary changes in the positions of the lasting atoms.

For the psychologist there is no hope of finding such necessity in the mental processes. The point is not that psychology is to-day too far removed from the fulfillment of such an ideal, the point is rather that such an ideal would be meaningless for the psychologist. His materials, the psychical contents of consciousness, are by their nature unfit to enter into such necessary connections; they cannot do it because they cannot last. The physical object, we saw, is the object which is common property, which we all feel in common, which must thus exist for all time. The things in nature may burn down or decay, but no atom of them can ever disappear from the universe, each must enter into new and ever new combinations and last through all changes. The psychical thing, on the other hand, can exist only for the one immediate experience. Every sensation which enters into my ideas or volitions or emotions is a new creation of the instant which cannot last; each one flashes up and is lost with the moment's experience. My will to-day may have the same aim as my will of yesterday, but as psychical object, my will to-day is a new will, is a new creation in every pulse beat of my life. I must will it again, I cannot store it up. And my joy of to-day can never be as psychical fact the same joy which I may have to-morrow. Mental objects as such, as psychological material, are not destined to last. It has no meaning whatever to think of their being kept over until another time. It is a coarse materialism to conceive the mental contents like pebbles which may remain on the road from one day to another. Our ideas and feelings are mental appearances which have their existence in the act of the one experience; each new experience must be an entirely new creation.

If I remember my last year's perception, I do not dig it out from an under-mind, in which it was stored up and buried, but I create an entirely new memory picture, just as I may make to-day a speech which says the same thing which I said last year, and yet my action of speaking is not last year's speech movement. It is a new action, and the movement did not lie over somewhere during the interval. Mental life is produced anew in every moment. When the first experience is gone and the second comes, nothing of the stuff from which the first was made still has existence in the content of consciousness. By this fact it becomes entirely impossible ever to conceive necessary connections in the sense of physical necessity in the world of consciousness. The one idea may bring to me another idea by association, but as long as I consider both strictly as mental facts, I can never understand why this association happens, I can never grasp the real mechanism of the connection, I can never see necessity between the disappearance of the one and the appearance of the other. It remains a mystery which does not justify any expectation that the same sequence will result again. Whatever belongs to the psychical world can never be linked by a real insight into necessity. Causality there remains an empty name without promise of a real explanation.

Only when we have recognized this fundamental difficulty in the efforts for psychological explanation, can we understand the way which modern psychology has taken most successfully. The end of this way is simply this: every psychical fact is to be thought of as an accompaniment of a physical process and the necessary connections of these physical processes determine, then, the connections of the mental facts. Indeed this has become the method of modern psychology. It has brought about the intimate relation between psychology and the physiology of the brain, and has given us, as foundation, the theory of psychophysical parallelism; the theory that there is no psychical process without a parallel brain process. But the real center of the theory lies indeed in the fact which we discussed; it lies in the fact that we cannot have any explanation of mental states as such at all, if we do not link them with physical processes.

Is it necessary to express again the assurance that such statements of a parallelism between mind and brain in no way interfere with an idealistic view of inner life? Have we not seen clearly enough that these mental facts which are conceived parallel to physiological brain processes do not represent the immediate reality of our inner life, that our life reality is purposive and as such outside of all causal explanation, and that we have to take a special, almost artificial, point of view to consider inner life at all as objects, as contents of consciousness, and thus as psychological material? But since we have seen that for certain purposes such a point of view is necessary, as soon as we have taken it we must be consistent. Our inner life in its purposive reality has therefore nothing to do with brain processes, but if we are on the psychological track and consider man as a system of psychological phenomena, then to be sure, we must see that our only possible interest lies in the finding of necessary causal connections. But these cannot be found otherwise than by linking the mental facts with the physical ones, the psychological material with the processes of the brain.

Of course, that mental experience stands in intimate relations to the body is a knowledge which does not wait for such philosophical arguments. That mind and body come in contact is a conviction which goes with every single sense perception. I see and hear because light and sound stimulate my sense organs, and the sense organs stimulate my brain. The explanation of perception through causes in the physical system seems the more natural as it is evident that in such cases there are no psychical causes which might have brought forward the perception. If I suddenly hear bells ringing, there was on the mental side nothing preceding which could be responsible for my sound perception. And the same holds true if the physical source lies in my own body, if perhaps my tooth begins to ache, although no expectation preceded it.

In the same way it seems a matter of course that mind and body are connected wherever an action is performed. I have the will to grasp for the book before me, and obediently my arm performs the movement; the muscles contract themselves, the whole physical apparatus comes into motion through the preceding mental fact. The same holds true where no special will act arouses the muscles. If a thought is in my mind and it discharges itself in appropriate words, those words are after all as physical facts the movements of lips and tongue and vocal cords and chest; in short, a whole system of physical responses has set in through a mental experience. But the same thought may be the starting-point for many other bodily changes; it may make me blush, and that means that large groups of blood-vessels become dilated; or I may get pale, the blood-vessels are contracted. Or I may cry, the lachrymal gland is working; or it may spoil my appetite, the membranes of my stomach cease to produce; or my muscles may tremble, or my skin may perspire; in short, my whole organism may resound with mental excitement which some words may set up.

But it is not only the impression of outer stimuli and the expression of inner thoughts in which mind and body come together. Daily life teaches us, for instance, how our mental states are dependent upon most various bodily influences. If the temperature of the blood is raised in fever, the mental processes may go over into far-reaching confusion; if hashish is smoked, the mind wanders to paradise, and a few glasses of wine may give a new mental optimism and exuberance; a cup of tea may make us sociable, a dose of bromide may annihilate the irritation of our mind, and when we inhale ether, the whole content of consciousness fades away. In every one of these cases, the body received the chemical substance, the blood absorbed and carried it to the brain, and the change in the brain was accompanied by a change in the mental behavior. Even ordinary sleep at night presents itself surely as a bodily state—the fatigued brain cells demand their rest, and yet at the same time the whole mental life becomes entirely changed. It is not difficult to carry over such observations of daily life to the more exact studies of the psychological laboratory and to examine with the subtle means of the psychological experiment the mental variations which occur with changes of physical conditions. We might feel, without instruments, that our ideas pass on more easily after a few cups of strong coffee, but the laboratory may measure that with its exact methods and study in thousandth parts of a second, the quickening or retarding in the flow of ideas. Every subjective illusion is then excluded, our electrical clocks, which measure the rapidity of mental action and of thought association, will show then beyond doubt how every change in the organism influences the processes of the mind. Bodily fatigue and indigestion, physical health and blood circulation, everything, influence our mental make-up. In the same way it is the laboratory experiment which shows by the subtlest means that every mental state produces bodily effects where we ordinarily ignore them. As soon as we apply the equipment of the psychological workshop, it is easy to show that even the slightest feeling may have its influence on the pulse and the respiration, on the blood circulation and on the glands; or, that our thoughts give impulse to our muscles and move our organs when we ourselves are entirely unaware of it.

Again we may turn in another direction. Pathology shows us how every physical disablement of the brain is accompanied by mental processes. If the blood supply to the brain is cut off, we faint; a blow on the head may wipe out the memory of the preceding hours, and a hemorrhage in the brain, the bursting of a blood vessel which destroys groups of brain cells, produces serious defects in the mental content. A tumor in the brain may completely change the personality; the bodily disease of certain convolutions in the brain brings with it the loss of the power of speech; paralysis of the brain dissolves the whole mental personality. Physical inhibition in the growth of the brain involves, on the mental side, feeble-mindedness and idiocy. Of course, all this is not sufficient to bring out a definite parallelism between special mental functions and special physical processes, as the phenomena are extremely complex. If a patient who has suffered from a mental disturbance dies, and his brain is examined, there is no simple correlation before us. It may be difficult to diagnose exactly the mental symptoms. If we have heard that the man was unable to read, we do not know from that what really happened in his brain. He may not have read because he did not see the words, or because the letters were confusing, or because he had lost memory for the meaning, or because he had lost the impulse to speak the words, or because he felt unable to turn his attention, or because the impulse to read aloud was not carried out by his organism, or because an inner voice told him that it is a sin to read, or for many similar reasons; and yet each one represents psychologically an entirely different situation. On the other hand, on the physical side, the destruction is probably not confined to one particular spot. Complications have crept over to other places or the disturbance in one part works as inhibitory influence on other brain parts, or a tumor may press on a far-removed part, or the disturbance may be one which cannot be examined with our present microscopic means. In short, we have always a complex mental situation and a complex physical one, and to find definite correlations may be possible only by the comparison of very many cases.

Other methods, however, may supplement the pathological one. The comparative anatomist shows us that the development of the central nervous system in the kingdom of animals goes parallel to the development of the mental functions, and that it is not only a question of progress along all lines. Any special function of the mind may have in certain animal groups an especially high development, and we see certain parts correspondingly developed. The dog has certainly a keener sense of smell than the man—the part of the brain which is in direct connection with the olfactory nerve is correspondingly much bulkier in the dog's brain than in the human organism. Here too, of course, research may be carried to the subtlest details and the microscope has to tell the full story. Not the differences in the big structure, but the microscopical differences in the brain cells of special parts are to be held responsible. But comparison may not be confined to the various species of animals; it may refer not less to the various stages of man. The genetic psychologist knows how the child's mind develops in a regular rhythm, one mental function after another, how the first days and first weeks and first months in the infant's life have their characteristic mental possibilities, and no mental function can be anticipated there. The new-born child can taste milk, but cannot hear music. The anatomist shows us that correspondingly only certain nervous tracts have the anatomical equipment by which they become ready for functioning. Most of the tracts at first lack the so-called medullar sheath, and from month to month new paths are provided with this physical equipment.

Finally we have the experiment of the physiologist. His vivisectional experiments, for instance, demonstrate that the electrical stimulation of a definite spot on the surface of a dog's brain produces movements which we should ordinarily take as expressions of mental states, movements of the front legs or of the tail, movements of barking or whining. On the other hand, the dog becomes unable to fulfill the mental impulses if certain definite parts of his brain are destroyed. The physiologist may show from the monkey down to the pigeon, to the frog, to the ant, to the worm, how the behavior of animals is changed as soon as certain groups of nervous elements are extirpated. It is the mental emotional character of the pigeon which is changed when the physiologist cuts off parts of his brain. In short, stimulation and destruction demonstrate, by experiments which supplement each other, that mental functions correspond to brain functions.

There is thus no lack of demonstration from all quarters that mental facts and brain processes belong together; and yet, however much we may cumulate such popular and scientific observations, they would never by themselves admit of the sweeping generalization that there cannot be any mental state which is not accompanied by a process in the central nervous system. Someone might say, to be sure, the perceptions and memory images, the volitions and instincts and impulses, have their physiological basis, but there remain after all acts of attention, or decisions, or subtle feelings, or flights of imagination, which are independent of any brain action. Here, indeed, observation cannot settle such a general principle. Its real hold lies in the fact with which we started: there is no causal connection in the mental states as such. If we want to understand mental facts as such in a chain, of causal events, we have first to conceive them as parallel to physical events. The principle of psychophysical parallelism, that is, the principle that every psychical process accompanies a physiological change is thus not a mere result of observation. It is simply a postulate. Every science begins with postulates and only that which fulfills such postulates has the dignity of truth in the midst of that scientific realm. The astronomer cannot find by observation that there is no star the movements of which are not the effects of foregoing causes. He knows it beforehand, he demands it, he does not recognize any movement as understood until he has found the causes, he presupposes that such causes exist, that no star moves simply by a magic power, and that nowhere in the astronomical universe is the chain of causality broken. He postulates it, and where he does not discover the causes, he is sure that he has not solved the real problem.

In the same way the psychologist who aims towards explanation of mental facts must postulate that there cannot be any mental state which is not an accompaniment of a physical brain process, and is as such connected through physical means with the preceding and the following events in the psychophysical system. Only when such a general framework of theory is built up by a logical postulate, is the way open to make use of all those observations of the laboratory and of the clinic, of the zoÖlogist and of the anatomist. It is the theory which has to give the right setting to those scattered observations. However far we may be from being able to point to the special brain process which lies at the bottom of the higher mental state, we know beforehand that there is no shadow of an idea, no fringe of a feeling, no suggestion of a desire which does not correspond to definite processes in the brain. The details may and must be material for diverging theories, but the conflict of such hypothetical opinions has nothing to do with the certainty of the underlying conviction that if we knew the whole truth, we should recognize every single mental happening as parallel to physical processes in the nervous system. To explain mental facts means to think them as parallel to the brain processes which have their own causal connections in the physical world.

We started, for instance, from the old observation that two impressions which come to our mind at the same time have a tendency to reawaken one another; and we saw that psychology was well able to formulate these facts in general statements of the association of ideas. But we realized that that in itself is not really explanation. If the odor which we smell awakes in us the name of a chemical substance, and if we now bring this under the general heading of association of ideas, an explanation is not really given by it. That smell sensation itself is not really understood as a cause of those sound sensations of the word. We have no insight into the connection of those two happenings. But the situation is entirely changed, if we consider the smell effect from the point of view of the parallelistic theory. Now the association of facts would indicate that we got the first two impressions together, because two brain processes were going on at the same time. My nose brought me the smell stimulus, my ear gave me the sound stimulus, each going on in a particular center, or, to express it in a simplified schematic way, each reaching particular brain cells, and the excitement of these brain cells being accompanied by the particular sensations. The physiologist has many possibilities of conceiving the further stages of the process, in order to satisfy the demand of explanation. He may say the excitement of each of these two brain cells, the one in the olfactory center, the other in the auditory center, irradiates in all directions through the fine branches of the brain fibers. Each cell has relations to every other cell in the brain; thus there is also one connecting path between those two cells which were stimulated at once. Now if the two ends of an anatomical path are excited at the same time, the path itself becomes changed. The connecting way becomes a path of least resistance, and that means that if, in future, one of the two brain cells becomes excited again, the overflow of the nervous excitement will not now go on easily in all directions, but only just along that one channel which leads to that other brain cell. A theory like this explains in real explanatory terms, in ways which physics and chemistry can demonstrate as necessary, that any excitement of the odor cell runs over into the sound cell and vice versa. In short, the psychological association of ideas, which we should simply have to accept as inexplainable fact, is thus transformed into a connection which we understand as necessary; and the fact is really explained.

This simple scheme of the physiology of association for a hundred years has given a most decided impulse to the progress of psychology. As the association process can so easily be expressed in physiological terms, the aim was prevalent to understand the interplay of mental life more and more as the result of association. The underlying thought of this whole association psychology was thus a conviction that whenever two mental experiences occur together, either of them keeps the tendency to reawaken the other at a later time. Through the endless combination which life's impressions awaken in the mind from the first hour after birth, the whole stream of memory images and thoughts and aims and imaginations is thus to be explained.

The whole theory of physiological associationism works evidently with two factors. First, there are millions of brain cells of which each one may have its particular quality of sensation, and second, each brain cell may work with any degree of energy, to which the intensity of the sensation would correspond. If I distinguish ten thousand different pitches of tone, they would be located in ten thousand different cell groups, each one connected through a special fiber with a special string in the ear. And each of these tones may be loud or faint, corresponding to the amount of excitement in the particular cell group. Every other variation must then result from the millionfold connections between these brain cells. Indeed, the brain furnishes all possibilities for such a theory. We know how every brain cell resolves itself into tree-like branch systems which can take up excitements from all sides, and how it can carry its own excitement through long connecting fibers to distant places, and how the endings of these fibers clasp into the branches of the next cell, allowing the propagation of excitement from cell to cell. We know further how large spheres of the brain are confined to cells of particular function, that for instance cells which serve visual sensations are in the rear part of the brain hemispheres, and so on. Finally we know how millions of connecting fibers represent paths in all directions, allowing very well a coÖperation by association between the most distant parts of the brain. The theories found their richest development, when it was recognized that large spheres of our brain centers evidently do not serve at all merely sensory states, but that their cells have as their function only the intermediating between different sensory centers. Such so-called association centers are thus like complex switchboards between the various mental centers. Their own activity is not accompanied by any mental content, but has only the function of regulating transmission of the excitement from the one to the other. Above all their operation would make it possible that through associative processes, the wonderful complexity of our trains of thought may be reached.

Yet even the highest development of the association theories did not seem to do justice to the whole richness of the inner life. We may well understand through those association processes that a rich supply of memory pictures is at our disposal, that ideas stream plentifully to our minds and enter into new and ever new combinations. But that alone is not an account of our inner experience. If there is anything essential for inner life, it is the attention which gives emphasis to certain states and neglects others. And that means that certain mental contents are growing not only in strength but in vividness and clearness, and that others are losing their vividness, are inhibited and suppressed. Here were always the real difficulties of the association theories; they seemed so entirely unable to explain from their own means why certain states become foremost in our minds and others fade away, why some have the power to grow and others are neglected. These facts of attention and vividness, inhibition and fading, worked almost as a temptation to give up the physiological explanation altogether and to rely on some mystical power, some mental influence which could pull and push the ideas without any interference and help from the side of the brain. Yet since we have seen that the truth of psychophysical parallelism has the meaning of a postulate which we cannot escape unless we want to give up explanation altogether, it is evident that such falling back into un-physiological agencies would be just as inconsistent as if the naturalist should posit miracles in the midst of chemistry or astronomy. If the facts which cluster about attention cannot be understood by the simple scheme of associationism, the demand must be for a better physiological theory.

The development of physiological psychology in recent years has indeed shown the way to such a wider theory, which furnishes the physiological accompaniment also for those experiences of attention and vividness which form the weakness of associationism. This new development has come up with the growing insight that the brain's mental functions are related not only to the sensory impressions, but at the same time to the motor expressions. The older view, still prevalent to-day in popular writings, made the brain the reservoir of physical stimuli, which come from the sense organs to the cortex of the brain hemispheres. There the perceptions arose and through associative interplay the memory pictures and the ideas of action and the feelings arose, and the whole inner life was thus bound up with the processes in these sensorial spheres. When the mind had done its work, finally an impulse was sent to some motor apparatus in the brain which then sent off the impulse to some acting muscles. That whole motor part was thus a kind of appendix to the brain process. The psychical life had nothing to do with it but to give the command for its action. The process in the motor part thus began when the mental proceeding was completed. But it became clear that this view was only the outgrowth of the strong interest which physiology took in the sense processes. If a neutral fair account of the brain actions is attempted, there can hardly be doubt that this whole sensorial view of the brain is only half of the story and that the motor half has exactly the same right to consideration. The cortex of the brain, the functions of which are accompanied by mental processes, is always and everywhere not only the recipient of sensory stimuli but at the same time the starting point of motor impulses. That which is centripetal, leading to the cortex, is therefore not more important for the central process than that which is centrifugal, leading from the cortex. The cortex is the apparatus of transmission between the incoming and the outgoing currents, between the excitements which run to the brain and the discharges which go from the brain, and the mental accompaniments are thus accompaniments of these transmission processes. If the channels of discharge are closed and the transmission is thus impossible, a blockade must result at the central station and the accompanying mental processes must be entirely different from those which happen there when the channels of discharge are wide open. Here too all the special theories are still in the midst of tumultuous discord. Yet this new emphasis on the motor side of the psychical process seems to influence modern psychology more and more.

Nobody can deny that first of all this is the necessary outcome of a biological view of the brain. What else can be the brain's function in the midst of nature than the transforming of impressions into expressions, stimuli into actions? It is the great apparatus by which the organism steadily adjusts itself to the surroundings. There would be no use whatever biologically in a brain which had connections with the sense organs, but which had no connections with the muscular system, and on the other hand, a brain which had motor nerves and muscular adjustment would be entirely useless if it had not sensory nerves and sense organs connected with it. In the one case the world would be experienced, but no response would be possible; in the other case, the means for response would be given, but no adjustment could set in because no experience of the surroundings would be possible. Adjustment every moment demands the relation of the brain in both directions. Through the sensory nerves the brain receives; through the motor nerves the brain directs, and this whole arc from the sense organs through the sensory nerves, through the brain, through the motor nerves and finally to the muscles, is one unified apparatus of which no part can be thought away. The brain in itself would be just as useless for the organism as the heart would be without the arteries and veins.

We must keep this intimate and necessary relation between the sensory and motor parts constantly in view, and must understand that there cannot be any sensory process which does not go over into motor response. Then only the ways are open to develop physiological views which give a physical basis to the processes of attention and vividness and inhibition, just as well as to the processes of memory and association. Such motor theories take many forms. Perhaps we shall most quickly bring the most essential factors together, if we say that full vividness belongs only to those sensations for which the channels of motor discharge are open, while those are inhibited for which the channels of discharge are closed; and any channel of discharge is closed, if action is proceeding in the opposite channel. If I open my hand, the motor paths which lead to closing my fist are blocked; and if I close my fist, the channels which lead to the opening of the hand are closed. Now if only those ideas are vivid which find the channels open, it is clear that all the ideas which would lead to the opposite action have no chance for development; they remain inhibited, and just this relation between the vividness of certain ideas and inhibition for those ideas which lead to the opposite action is the characteristic of the process of attention.

From such a point of view, the total mental life can be brought into the psychophysical scheme. We now have not two variable factors, but three, namely, the qualities of the elements, the intensities of the elements, and, as a third, the vividness of the elements. The quality corresponds, as we saw in the association theory, to the local position and connection of the brain cells; the intensity corresponds to the energy of the excitement; and the vividness, we may add now, corresponds to the relation to motor channels. The whole mental life thus becomes the accompaniment of a steady process of transmitting impressions and memories into reactions. That every experience involves millions of such elements we saw when we spoke of the description of mental life. The effort to explain mental life shows us now that this millionfold manifoldness belongs to a system of reactions of which all parts are in steady correlation: a moving equilibrium of unlimited complexity. Surely no one can reduce this wonderful manifoldness to those clumsy concepts with which popular psychology is reporting the story of the mind and its relations to the brain.

It may seem that such a psychological view of inner life annihilates that which we feel as the most essential characteristic of our inner experience, its unity and its freedom. In one sense that is certainly true. In the real life which we live and fight through, where our duties and our happiness lie, we know a unity and freedom of our personality which psychology must destroy. Of course that does not mean that psychology denies the truth of that freedom and unity. Moreover it would condemn itself if it were to deny that which gives meaning to the endeavors of our life and thus also to every search for truth. Psychology claims only that we must abstract from it, when we take the psychological standpoint towards life. Freedom of our real life means that we must know ourselves in the midst of our life work as guided by aims and obligations, and that in this purposive existence of ourselves we do not feel ourselves as determined by causes. I will the fulfillment of my ideals only because I will them. That this will itself may be the effect of foregoing causes is an aspect which does not belong to my naÏve experience. Our freedom means that in our real life our will is not related to causes, that the point of view of causality is thus meaningless for the value of our achievements. And the other man's will too comes in question for us as something to be interpreted and to be appreciated, but not to be explained by connection with causes. As long as we move in this sphere of purposive interest, we are free and deal with free selves; but if in the midst of these free aims, the will arises to consider the actions of others and of ourselves from the standpoint of causality, then we have ourselves decided to enter a new sphere in which it would be meaningless to seek for any will which is not determined by causes. As soon as we have chosen the psychological standpoint and are in the midst of the work of causal reconstruction, any will which is not understood as determined by causes is simply an unsolved problem. In the midst of a causal construction, absence of causes would never mean real freedom.

In that purposive world of immediate life experience, we also are unities inasmuch as we ourselves know us as the same in every new will of ours. We remain identical with ourselves because every purpose is posited in the midst of, and bound up with, the general purpose of ourselves. And in this internal unity of meaning, nothing breaks ourselves into pieces, and the whole manifold of experience is thus expressed by a personality which knows itself in its purposive unity. But this unity again is denied by our own intention as soon as we decide to take the causal view of inner life. The purposive unity must now transform itself into an endless complexity, and our own self becomes a composite of hundreds of thousands of elements.

On the other hand, all this does not mean that psychology cannot have its own consistent conception of the mind's unity and freedom. Our psychological mind is a unity because its manifold is a system in which all parts hang together. A change in any one part involves changes in the whole system. The interrelation, to be sure, is not a strictly psychical one, for we have seen that the causal connection as such appears at the physical side. But, inasmuch as there is no psychical process which does not belong to a physiological one, the interconnection of the mental facts is complete and involves the totality of neural processes of which after all a small part only has its psychological record. We might compare those hundreds of millions of neurons in each brain with the hundreds of millions of individuals who make up the population of the nations, and the psychical accompaniment we might compare with the written historical record of mankind. The written records themselves have no direct interconnection, they are only accompaniments of what happens in these millions of men. And again only the higher layer of the neurons in the population sees its doings recorded in the annals of history; and yet whatever those leaders of action and thought and emotion may achieve is dependent upon and working on the actions of those millions of subcortical population neurons. The historical record has its unity through the interrelation of all parts of historical mankind.

But after all the psychologist has no less a right to speak of freedom. Of course his freedom cannot mean exemption from causality. Whatever happens in the psychological system must be perfectly determined by the foregoing causes. But the psychologist has good reason to discriminate between those actions which result from the normal psychophysical factors and such actions as result from broken machinery. If the brain is poisoned by alcohol or in fever, if an infectious disease has destroyed the brain cells, action is no longer the outcome of the normal coÖperation of the organs, and even those clusters of neural activities which are accompanied by the consciousness of the own personality lose their control of the motor outcome. The man in delirium or paralysis acts without causal connection with his past; the action is, therefore, not the product of his whole personality, and the psychologist is justified in calling the man unfree. But, whenever the motor response results from the undisturbed coÖperation of the normal brain parts, then the inherited equipment and the whole experience and the whole training, the acquired habits and the acquired inhibitions will count in bringing about the reaction. This is the psychological freedom of man. The unity of an interconnected composite and the freedom of causal determination through normal coÖperation of all its parts characterize the only personality which the psychologist has to recognize.