The Nature of Intelligence

Chapter 1. The Stimulus-Response Fallacy in Psychology

L.L. Thurstone

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1. The old and the new psychology
2. Stimulus-response
3. The dynamic self
4. The psychological act
5. Psychology as a science
6. Stimulus-response in the animal mind
7. Summary


There has lately come into prominence before the reading public what is known as the New Psychology. This so-called new psychology is concerned with a wide variety of mental phenomena which have a strong interest appeal to every intelligent person. It purports to explain to us our dreams, our slips of the tongue, our forgetting, our prejudices, how personality is made, and many other mysteries in which we are all interested. It deals with considerable confidence in the problems of capital and labour, economic motives, peace and war. No wonder that it is attracting attention.

As we read the literature of the new psychology we stop to recall our psychological reading of ten or fifteen years

(2) ago, and we find that the two kinds of psychology do not even use the same language. The terminology is entirely different. In the psychology which has become established in universities, the categories include sensation and perception, imagination, reasoning, the sense organs, memory, the affective states, and so on. These terms have a familiar sound to anyone who has ever taken a course in psychology. In the new psychology we read about complexes, rationalization, projection, compensation, identification, symbolism, repression, the wish, and many other categories that do not even occur in the indexes of standard textbooks of the subject. What is the fundamental reason for the disparity between the established type of psychological discourse and the so-called new psychology ?

There are several factors that contribute toward this disparity in psychological language, and it is well to keep them in mind in order to understand the present tendencies in the interpretation of mental phenomena. First we must recall the different origins of the old and of the new psychology. The old psychology was written partly by philosophers and later by psychologists who devoted themselves to the scientific study of mind. The new psychology and particularly psychoanalysis has been developed by those physicians who have devoted themselves primarily to the treatment of mental disorder. Here we have two different types of training for the men who represent the two different types of psychology. In general, a fair-minded student would probably admit that the new psychology deals with subjects that are more generally interesting than those which he may recall from his textbooks. On

( 3) the other hand, one must admit also that the psychology of the standard textbooks is written with greater regard for scientific consistency. The new psychology has very little regard for scientific method, and it does not rest on careful experimental work to ascertain the facts. Nevertheless, the new psychology has a strong appeal to our interests, and in large part its propositions seem to be very plausible. It is only natural that the physicians who devote themselves primarily to the treatment of disordered minds should pay attention mostly to the methods that work, while the psychologists, as scientists, should pay attention mostly to the scientific experimental methods for establishing facts.

Another factor that partly explains the difference between the new psychology and the old is to be found in the character of the mental phenomena that are the basis of the two schools. The psychiatrist deals with minds that are abnormal, minds that have broken under stress of some kind. The psychologist deals with normal minds, minds that are sufficiently calm, quiet, and contented, to submit in the psychological laboratory to experimentation. Obviously the materials on which the two schools of psychology are built up differ at the very source of the observations.

The normal person who has sufficient leisure to serve as a subject of experimentation in the psychological laboratory is not likely to have any major mental disturbance and distress. If, on the occasion of a Peaceful psychological experiment, he is mentally disturbed by any serious issue in his fundamental life interests-financial, sexual, social, professional, physical-he reports that he is indisposed,

( 4) and he does not serve as a subject. It is therefore relatively seldom that the psychological laboratory gets for observation persons who are in a mental condition of major significance. The psychiatrist, on the other hand, continually observes persons whose mental states are dominated, or broken, by issues that are close to the fundamental mainsprings of life.

It is only reasonable, therefore, that we should find a fundamental difference between the new and the old psychology as regards the significance of the mental phenomena that they represent. The established forms of psychological discussion relate mostly to the momentary mental states and related phenomena, such as the sense qualities, colour mixture, the taste buds, the visual illusions, the reflexes, peripheral vision, reaction time, the learning and forgetting of nonsense syllables, the fields of attention, visual and auditory imagery, the momentary nature of emotion, the difference between instinctive and habitual actions. All of these, and in fact most of the discussions in the standard textbooks of psychology, refer to the momentary mental states, situations in which a laboratory experiment may be prepared and in which the subject reports what he at that moment sees, or hears, or feels. There is no criticism to be made against all this scientific experimentation except that it seldom relates to the permanent life interests of the persons who lend their minds to the psychological experiments.

In the new psychology we deal, on the other hand, with a whole series of explanatory categories that have their origin in the psychopathic hospitals, where every person

(5) observed is giving vent to a disturbance in the fundamental and permanent mainsprings of his life. This contrast between the new psychology and the old is summarized by noting that the established forms of psychological writing deal mostly with the momentary mental states, while the new psychology deals mostly with the expression of basic and permanent human wants.

There are, of course, many secondary branches of these two large schools of psychology, and there is an ever-increasing number of men who can straddle both schools ; but it is clear that their interest in the permanent life motives comes from their clinical experience, while their interest in rigorous scientific experimentation comes from the peaceful psychological laboratory in the college.

The two schools represent two widely differing points of view in the study of the mind, and it is our purpose in these chapters to assist in bridging the gap so as ultimately to combine the worthy features of both schools of thought into a consistent interpretation of the human mind.

One of the basic differences between the old and the new psychology is in the treatment of the stimulus or environment. Writers of the academic schools of psychology treat the stimulus as the datum for psychological inquiry. They put their subject into the laboratory, and confront him with stimuli of various kinds, colours, noises, pains, words, and with the stimulus as a starting-point they note what happens. The behaviour of the person is interpreted largely as a mathematical function of the stimulus or environment. The person's own inclinations are of course recognized as constituting a factor in the

( 6) situation, but only as a modifying factor. The stimulus is treated as the datum or starting-point, while the resulting behaviour or conduct is treated as the end-point for the psychological inquiry. The medical writers on psychology state or imply a very different interpretation of the stimulus. Here, the starting-point of conduct is the individual person himself. He wants certain things, he has cravings, desires, wishes, aspirations, ambitions, impulses. He expresses these impulses in terms of the environment. The stimulus is treated by the new psychology as only a means to an end, a means utilized by the person in getting the satisfactions that he intrinsically wants. This is a very basic contrast. In the older schools of psychology we have the characteristic sequence : the stimulus--the person--the behaviour. The behaviour is thought of mainly as replies to the stimuli. In the newer schools of psychology we have a different characteristic sequence : the person --the stimulus--the behaviour. The stimulus is treated merely as the environmental facts that we use to express our purposes.


In the current academic psychology we teach a stimulus-response formula about which everything else psychological revolves. The contributions of the newer schools of psychology are certain to modify the rigidity of this formula. By the stimulus-response formula, is meant the constant resolution of every psychological problem into three conventional parts : the stimulus, which is treated as a first cause, the mind or central nervous system, and the behaviour,

The Stimulus-Response Formula

( 7) which is treated as a reply to the stimulus. After some practice this formula becomes so thoroughly ingrained that every psychological question is habitually broken up into a search for the provocative stimulus, a description of the resulting mental states, and a description of the responsive behaviour.

When a mental phenomenon is to be explained, many psychologists and educators of the older schools proceed somewhat as follows. What was the stimulus ? Describe it. What was the muscular response ? Describe it objectively. What happened between these two things ? There were " bonds " between them, and " pathways ", and " grooves " ; and " processes " took place, and there were " connexions " in the nervous system between the stimulus and the response. That settles it, and the event is psychologically explained. In order to make it clear they draw three lines on the blackboard with " fuzzy " ends to represent neurones and synapses. (See Fig. 1.) The three parts of the conventional analysis are represented diagrammatically by three neurones, one for the sense organ which receives the stimulus, one or more representing the central nervous system, and one representing the innervation of a muscle. Here we have the basic formula for psychological analysis as it is currently taught. Behaviour or conduct begins with a stimulus, and' it ends with a muscular response. One cannot read the authors who represent the findings of abnormal psychology without becoming sceptical about the adequacy of this stimulusresponse formula to which we have long been accustomed, although none of these writers explicitly attack the formula as such.

( 8)

In Fig. 2 the two contrasting points of view are represented in a diagrammatic way. The generally current formulation is represented in the upper part of the diagram. A stimulus hits us. The mind consists of the so-called bonds and pathways, and out comes the response. When we see a muscular adjustment, we point to a known, or unknown, stimulus which has found its way transformed through bonds and pathways into our conduct. It would hardly be fair to say that we are always as totally unmindful of the mental in our mental science as the simple diagram would indicate. And yet, the great majority of discussions in psychology are carried out with this formula, either explicitly or by implication. To the student who approaches the study of psychology in expectation of discovering how his mind works, it is often a legitimate disappointment for him to learn that psychologists have reduced his mind to three unmental categories, the external physical stimulus, or the physiological stimulus, the bonds and pathways which dispose of everything mental, and the physical muscular behaviour. To relegate habitually our mental life into the unmental stimulus-response categories is a procedure which carries the appearance of science in its terminology, but which is not infrequently indicative of a superficial and unsympathetic understanding of mental life.

In the second part of Fig. 2 I have represented the function which, it seems to me, the stimulus really serves. Let us start the causal sequence with the person himself. Who and what is he ? What is he trying to do ? What kind of satisfaction is he trying to attain ? What are the types of self-expression that are especially characteristic for him ? What are the drives in him that are expressing themselves

Figure 2, Alternative Formula

( 9) in his present conduct ? Consider the stimuli as merely the environmental facts in terms of which he expresses himself. In the diagram I have represented the causal sequence as starting with the dynamic living self. Self-expression is defined into particular actions at the terminal end of the diagram. The environment, the stimulus, is causally intermediate. The stimulus determines the detailed manner in which a drive or purpose expresses itself on any particular occasion.

In the diagram I have attempted to show that the stimuli may be considered as of three kinds with respect to the life impulse of the organism. First, we have the stimuli that promise satisfaction of an impulse. These stimuli call forth acts of appetition. Second, we have the stimuli that mean failure. These stimuli call forth acts of aversion. Both of these types of stimuli are perceived as significant and they are determinants of conduct. Third, we have the stimuli which are entirely indifferent with respect to the impulses of the organism. These stimuli call forth no variation in conduct. If, while walking to your office in the morning, you see a coal-wagon in front of you on the sidewalk, it is a stimulus which determines an avoiding reaction. It is antagonistic to your purpose of the moment. When you see your office door in front of you it determines a positive reaction because it becomes a part of your purpose at that moment. Most of the signs, stores, vehicles, and people are indifferent stimuli which are not even perceived because you do not identify them with your purpose at the moment. In the diagram are represented two stimuli which cause avoiding reactions, and a stimulus which causes a positive reaction. The stimuli

( 10) which are indifferent to the impulse or purpose are not represented in the diagram because they are not even perceived.

It is also possible to describe your actions according to the first formula. It is possible to say with accuracy that you have a visual impression of the coal-wagon, and that you respond to its presence by dodging it. The stimulus is then placed first, and your behaviour is said to be a response to the coal-wagon stimulus. The temporal sequence of such a description is correct. You first see the wagon, and then you dodge it. This is stimulus and response. It is apparent that both of these formulae may be used with some justice to the facts. It is preferable to use the second formula because it is much more powerful as an explanatory device for complex conduct. It must be remembered that even though the stimulus precedes the response, there is usually present a purpose or objective before the appearance of the stimulus.

There are situations in which the appearance of the stimulus is sudden, and in which there cannot be said to have been any conscious purpose before the appearance of the stimulus. Such is the case when suddenly you jump out of the way in response to a Klaxon horn. You do not then have a conscious purpose to jump before the sound becomes focally conscious. The stimulus appears to be the first cause in such a situation, and it would seem to be primarily provocative of the response. It would seem to fit the first formula better, but a second consideration would bring out the fact that we are always in readiness to maintain our physical, social, financial, professional selves. To be in constant readiness to maintain, defend,

( 11) and promote the self, in all its aspects, is the very essence of being alive. That is exactly the difference between an organism that is alive and one that is dead. We are so accustomed to this fundamental characteristic of every waking moment, the readiness to maintain the living self, that we do not notice it as a provocative cause for the things we do to maintain it. The Klaxon horn can then be thought of as merely the environmental circumstance at the moment by which you express that which was a part of you before the sound appeared. The sound merely determines the detailed manner in which you maintain yourself at this particular moment.


In the last analysis the datum for psychology is the dynamic living self and the energy-groups into which it may be divided. We may refer to this datum as the Will to Live, or we may call it the Life-impulse, or the Vitality of the organism, or we may discover it to be the energy released by metabolism. We may be able to subdivide our will to live into large energy-groups which manifest themselves in conduct more or less independently. These energy-groups would be our innate, dynamic, and more or less distinct sources of conduct, and we might come to call them drives, motives, instincts, determining tendencies, or any other word that represents that which we as individuals innately really are, that which characterizes us as persons with individually preferred forms of life.


The living self consists of impulses to action, and the conflicts of these impulses. The conscious self I have thought of as made up of impulses that are for some reason arrested while partly formed, incomplete impulses that are in the process of becoming conduct. By this I do not mean that conscious life is different from conduct, that conscious life is merely associated with conduct by any bonds or connexions. I mean that conscious life is made of the same stuff that conduct is made of. The only difference between an idea and the corresponding action is that the idea is incomplete action. Focal consciousness consists of, is actually made of, the impulses that are in the process of becoming conduct. The aggregate of these impulses, this incomplete conduct, constitutes the momentary " me ". The permanent and more or less predictable characteristics of these impulses constitute the self. The central subject-matter of psychology is the history of these impulses from their source in the metabolism of the organism to their partial expressions in thought, to their more complete formulation in perceived stimuli, to their final precipitation in overt conduct. Conscious life is incomplete action, behaviour which is, while conscious, not sufficiently specified to constitute any definite act. Consciousness consists in impulses that are still, while conscious, too unlocalized or universal to determine anything overt. Consciousness is the life impulse in the process of becoming conduct. To live is to telescope time.

With our interest thus centred on the dynamic aspects of the living person himself, we are in a position of good perspective from which to study the manner in which he utilizes the stimuli of his environment, the manner in

(13) which he goes about hunting for the stimuli that the environment does not immediately give, the manner in which his dynamic self finds overt expression through and by the stimuli that happen by chance to be available, and his compromises with substitute stimuli which in other moments he would reject as inadequate. The stimulus is not primarily provocative of living, of mental life. We, ourselves, are.


I have just said that the central subject-matter of psychology should be the history of impulses from their source in the metabolism of the organism through the intermediate stages of formulation in which they constitute mental states, to their final expression in conduct and satisfaction to the actor. This sequence begins in the organism itself and it terminates in satisfaction to the organism itself. Between the provocative condition of the organism, which starts random or purposive behaviour, and the satisfaction which terminates the provocation of behaviour, we have all the phenomena of mind. The history, or course of events, by which a craving or want becomes neutralized in satisfaction, I shall refer to as the psychological act. The psychological act starts in conditions about which we know extremely little. These conditions are determined, no doubt, by the physiological state of the organism. The state of nutrition has a lot to do with it. The balance of the ductless glands is no doubt an important provocative factor in behaviour.

The psychological act is an impulse which starts in an

(14) instinct condition. It develops into imagination by becoming more definite. It becomes still more definite when it seizes upon a sense impression as part of its own attributes. It defines itself completely when it issues in final overt form as action.

In Fig. 2 we have the psychological act divided, tentatively, into three phases : (1) the dynamic self as the origin of impulses that constitute living ; (2) the mental phase of these impulses in which they have taken some degree of definition or form ; and (3) the overt phase at which they have completed themselves in action. An overt act, the seen behaviour, is the terminal end of a psychological act. The latter consists not only of the seen conduct but also of the mental and physiological antecedents of conduct.


Every scientific problem is a search for the functional relation between two or more variables. This can be seen very clearly in the exact sciences, but it becomes more obscure as we enter the biological sciences, and it is frequently lost sight of in the social sciences. In physics we have, as typical problems, the search for relation between the length of time that a body has been falling and its speed, the pressure of a gas and its temperature or volume, the curvature of a lens and its focal distance, the resistance of a wire as determined by its cross-section or length, the pressure on a turbine as determined by the head in the penstock, the sag of a beam as determined by the load and the cross-section of the beam. Physicists and engineers

(15) come to look upon the search for relations between variables as the typical task of science. The attitude of looking for these relations becomes second nature to them. They reach habitually for a piece of cross-section paper in order to make a graph of the observations, and in order to visualize the nature of the relation that they are seeking.

In the biological sciences we have the same logic in the biometric methods. In the social sciences we are dealing, usually, with variables that are not quantitative, but there is no good reason why thinking in the social sciences should not follow the same logic even though the variables are often non-quantitative.

If every scientific problem is an attempt to state the relation between two or more variables, it should be profitable to note what the variables are that constitute scientific psychology. If we look over the field of experimental psychology, as it is represented by standard textbooks in the field, and by the work in psychological laboratories, we find that the relations into which the experimenters inquire classify themselves mostly in the following types :

(1) Relation between anatomy of the sense-organs and conscious sense-experience. Typical for such experiments are the studies to determine the relation between the touch, cold, and heat spots in the skin and the corresponding cutaneous sensations, or the sense qualities of colour that we have in the different parts of the retina. Another example would be the relation between the parts of the internal ear and sense-experience.

(2) Relation between stimuli and sense-experience. Here we have such typical laboratory experiments as the

( 16) determination of the laws of colour mixture. The relation studied is that between the description of the colours that are being mixed and the sense-experience which is the result.

(3) Relation between stimuli and muscular adjustment. The reaction time experiments are typical of this class. The reaction time experiment is an attempt to predict behaviour in terms of the conditions of the stimuli which are arranged as the cue for the behaviour.

Totally different is the fundamental nature of the relations that the medical writers in psychology are dealing with. They are constantly searching for the relation between the fundamental cravings and wants of people and the ways in which these wants are expressed. A patient talks and behaves as though he were an emperor, a millionaire, a person with power and fame. Let us contrast the two different scientific approaches of the old and the new psychology to this problem. What are the variables involved in the problem ? The psychologist of the established academic schools would ask about the stimuli, the environment, and he would state or imply in his solution that the patient is merely responding to stimuli. There might be some difficulty in specifying just what the stimuli are to which the patient is responding by talking like an emperor. The academic psychologist would list on one side of his scientific ledger the stimuli and environment to which the patient has been exposed, and on the other side of the ledger world be recorded the behaviour of the patient. The conduct would be described as a function of the environment, modified, to be sure, by the characteristics of the patient himself.


The psychiatrist would look for a different set of variables. He would list on one side of his ledger the wants and cravings of normal people, assuming that these wants are also part of the self of the patient, and on the other side of the ledger he would list the patient's conduct. The scientific problem would be to state how it comes about that the patient expresses in his particular way wants that are universal. The psychiatrist would treat the environment as merely the means by which the patient seeks to express wants and cravings that are universal. This procedure is much more powerful and illuminating. It shows us more about human nature, but it is not subject to the exact quantitative technique of the older sciences because the wants and cravings of normal people have not yet been classified and isolated in a measurable way.

Let us consider a typical laboratory experiment as another illustration. I have said that we are in the habit of describing action as a function of the stimulus. We place before a subject a tachistoscope, and he sees nonsense syllables. He tries over and over again until he has learned them. Out of this psychological experiment comes the scientific deduction that, other things being equal, he remembers best those syllables which are at the end of the list and which he saw last. He tends to remember also quite well those syllables that he saw first, before the novelty wore off. He does not remember so well the syllables in the middle of the list. This is a scientific experiment in which we state the relationship between two variables. The answers of the subject are described as a function of the stimulating nonsense. But how about

(18) incentives ? The most important factor is whether or not he cares about the nonsense syllables. This factor of interest and effort overshadows entirely the small effects of the arrangement of the syllables. The experiment is scientifically quite legitimate, but it is trivial in respect to the factors that are most important for mental life.

We recognize, of course, this fact, that incentives are more important than the arrangement of the syllables on the page in predicting the recall. But since the incentives are not readily measured, we rest content with describing the relations that we can measure. Well and good. This would not be subject to criticism if it were not for the fact that we have come to forget the individual person altogether. Experiments of this type have come to be the rule, and we have taken for granted that psychology is primarily concerned with the incidental relation between the response and the response-modifying stimulus. We have gone so far as to assert that psychology studies the stimulus-response relation, and we have forgotten the person himself who may or may not want to do the responding.

I suggest that we dethrone the stimulus. He is only nominally the ruler of psychology. The real ruler of the domain which psychology studies is the individual and his motives, desires, wants, ambitions, cravings, aspirations. The stimulus is merely the more or less accidental fact in the environment, and it becomes a stimulus only when it serves as a tool for somebody's purposes. When it does not serve as a tool for getting us what we want, it is no longer a stimulus. It is not a cause. It is simply a means by which we achieve our own ends, not those of

Figure 3, The Self-expression Formula

( 19) the stimulus. The psychological act which is the central subject-matter of psychology becomes then the course of events, primarily mental, which intervene between the motive and the successful neutralization or satisfaction of that motive. The stimulus appears somewhere between the provocative and the overt terminals of the psychological act. Mental life consists primarily in the approximate formulation of the motives leading toward overt expression. To the extent that mental life is of a relatively high order these approximate formulations of the motives become more and more tentative, deliberate, inhibited, delayed, and subject to choice before precipitating into their final overt form.

This point of view that I am recommending is not so radical as it might at first sight appear. What I am recommending is after all merely a shift of emphasis diagrammatically represented in Fig. 3. In that figure the upper line represents the causal chain tacitly followed by psychology as it is now usually written. This chain of events starts with the stimulus as the fundamental datum for psychological inquiry. From the stimulus as a source we trace the mental events to the response. Between these two terminals we place the characteristics of the individual in the form of modifying mental sets, predispositions, irritability, instincts, habits. We admit that the individual does enter into the causal chain but only as a modifier of the stimulus-response Series. When we. talk about instincts, for example, we look first of all for a suitable stimulus which can be given the credit for starting the instinctive behaviour. The stimulus is assumed to

( 20) be the absolutely essential starting-point for an instinctive act. At the other end of the causal chain we set down the characteristic behaviour which is brought about by the particular stimulus. Between these two events we assume that the individual himself has something to say but only as a modifier of the fundamental stimulus-response relation.

In the second line of Fig. 3, I have represented the individual and the stimulus as exchanging their places. The individual is in this second representation assumed to be the starting-point for that which he himself does. The stimulus takes the secondary rôle of modifier. The primary formula is then to be found in the impulse-conduct relation. The expression of the impulse is of course markedly affected by the stimuli, which are now to be considered as the momentary circumstances of the environment. I am simply shifting the stimulus to the secondary rôle of a modifier, and I am promoting the individual and his life impulses to the first rank of cause as far as psychology is concerned.

Consider the instinctive adjustments of retaliation against an insult. The insult would be described as a stimulus. Your defence would be described as a response. If you have lately been on the defensive as regards your position, professional status, financial security, or health, your motive of self-defence or self-preservation would have a low threshold. A trivial remark from an insignificant source might be sufficient to arouse defensive conduct on your part such as a fist blow, loss of temper, loud, self-assertive talk, sullenness, or a domineering manner towards

( 21) associates. If you have lately enjoyed a feeling of relative security with reference to your social, professional, financial, and physical self, the threshold for this defensive behaviour would be so high that the trivial remark would be passed unnoticed.

If you do reply to it, one would, of course, say that the insulting remarks came first, and that your reply came afterward. But such a stimulus-response analysis of the situation would be superficial. It would not be the remark that drove you on to defend yourself. The stimulus is only an environmental fact which determines partly how you express your desire at the moment. It is psychologically much more interesting to discover the tendencies that seek expression than to describe conduct as merely replies to stimuli.

Suppose that you are stuck on a country road on account of an engine which has been maltreated. There were surely stimuli that preceded your inspection of the engine. That which makes you do things to that engine is not primarily the stimuli from the engine-it is your desire to go. The stimuli are simply environmental facts which modify the expression of your desire to get there.

It may well be that our stimulus-response habits in psychological discussion came about because of the obvious fact that the stimulus often precedes conscious solution, and this in turn often precedes the overt act. The insulting remark no doubt preceded your back-talk, the engine balked before you looked for the trouble. That is all true, but your unsatisfied desire for security was active as an unlocalized irritability before the insulting remark was made, and your

( 22) desire to keep on going was being actively satisfied before the engine balked. The facts of temporal sequence should not blind us to the major causal factors of mental life.


This point of view is not limited to the interpretation of the human mind. It applies as well to the behaviour of the lower organisms. We are too often inclined to look upon the animal mind as consisting of nothing but reflexes acting in response to the stimuli that happen to strike it.

Let me quote from Jennings.[2] " Activity does not require present external stimulation. A first and essential point for the understanding of behaviour is that activity occurs in organisms without present specific external stimulation. The normal condition of Paramecium is an active one, with its cilia in rapid motion; it is only under special conditions that it can be brought partly to rest. Vorticella, as Hodge and Aikins showed, is at all times active, never resting. The same is true of most other infusoria, and, in perhaps a less marked degree, of many other organisms. Even if external movements are suspended at times, internal activities continue. The organism is activity, and its activities may be spontaneous, so far as present external stimuli are concerned . . . . The spontaneous activity, of course, depends finally on external conditions, in the same sense that the existence of the organism depends on external conditions. Reaction by selection of excess movements depends largely

(23) on the fact that the movement itself is not directly produced by the stimulus. The movement is due, as we have seen, to the internal energy of the organism . . . . The energy for the motion comes from within and is merely released by the action of the stimulus. It is important to remember, if the behaviour is to be understood, that energy, and often impulse to movement, comes from within, and that when they are released by the stimulus, this is merely what James has called 'trigger action '."

I will of course admit that the life-impulses depend on the environment. So does the very life of the organism. The life-impulse is derived from the metabolism of the organism, and this is in turn contingent on what the environment gives. That is all true. But I should insist that psychology begin with the life-impulse as its datum, and that it be concerned with the mental routes by which the impulse expresses itself.

The life-impulse has a history leading back to past stimuli, but the sequence from these stimuli to the accretion of vitality is a biological rather than a psychological problem. Except for some division of the task, one could readily find oneself arguing in a circle as to what it is that starts the whole business, the life-impulse or the stimulus. Mental life is an irreversible process beginning with the life-impulse and terminating in the successful overt act. The stimulus may be thought of as a means for specifying the approximate act which is mental. Present overt action, and the approximate actions which constitute mental life, can only very roughly be stated in terms of the individual's stimulus-history.


  1. Sections of this and the succeeding chapter as well as figures 2 and 3 have appeared in my article in the Psychological Review, vol. xxx, No. 5, September, 1923. They are reproduced here with the permission of the Editor.
  2. Jennings, H. S., Behaviour of the Lower Organisms, chaps. 16, 18.

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