Psychology in it Relation to Biology

Robert Yerkes

THERE was time when I agreed heartily with those who say, "What difference whether psychology he considered a part of biology or an independent science, should we not in either case work as we are working?" But recently an examination of my experience as teacher has convinced me of the incorrectness of this view. I note that within the past ten years, as a direct result of a radical alteration in my conception of the nature of psychology, I have almost completely changed the materials of my courses in the subject. What formerly I accepted as subject-matter of psychology and presented as such to my students, I now consider matter of neurology and general physiology; and, conversely, what I now deem the proper and important materials of psychology, I then either relegated to some branch of philosophy or ignored. This fact has sufficed to convince me, as no amount of theoretical discussion would have done, that one's conception of the materials, aims, and methods of his science is of profound practical importance in connection with both teaching and research. I wish, therefore, in the interests of what I consider to be a profitable view of the relations of psychology to biology, to report the results of a narrowly limited inquiry into the conceptions of psychology held by American biologists, to make a confession of faith, and to offer certain criticisms of psychology.

The aforesaid inquiry into the status of psychology in the minds of biologists was conducted primarily that I might learn whether the view which seems to me the best working conception is commonly held. Had my investigation proved it to be the dominant conception, I should not be writing this article.

Inasmuch as in this inquiry I prized quality of judgment above the number of opinions recorded, I sought the views of only a few individuals. To each of twenty eminently able and successful American biologists, of whom about one half are known to be predominantly morphological in their interests and the remainder physiological, I addressed the following questions: (1) Do you consider

( 114) psychology a part of physiology? (2) If so, please define the term psychology so that I shall clearly understand what it, includes.

At the time of writing I have received the replies of nineteen individuals. Of these replies four are non-committal, the writers frankly admitting that they have no reasonably satisfactory basis for an opinion; eight, with various qualifications, state that psychology is merely a part of physiology; and seven defend the view that it is an independent science, differing essentially in materials or methods, or both, from the biological sciences. Although it would add greatly to the interest and value of this discussion to publish the replies in full, I do not feel at liberty to do so, for the majority of my correspondents, in attempting to satisfy my request, felt keenly the limitations of their knowledge of psychology and expressed their views partly as a personal favor. In quoting from the opinions, I shall mention no names, but I wish to take this opportunity to express my appreciation of the kindness of my correspondents. I shall preface a general statement of the results of my inquiry with quotations from the replies to my questions. These quotations present the three types of conception of psychology which appear to be prevalent among the biologists of this country.

First Type of Conception.—"In my opinion," writes a biologist whose interests are medical, "psychology is a part of physiology. In reaching this conclusion, I assume that psychology is an expression of the activity of the brain, modified, perhaps, in some instances, by ductless glands. I take a purely material view and hold that, except as a mere matter of convenience, the term 'psychology' will in time disappear. As our knowledge of the functions of the central nervous system increases, we shall probably recognize a thought, a sentiment, a feeling, as being as much a matter of routine physiological action of the corresponding cells of the brain as a muscular action is."

This, I need not remind the reader, is a naked statement of mechanical materialism in psychology. It assumes that consciousness is a form of energy, and claims that it can be studied scientifically only as energy. At this point we are not concerned with comments or criticisms.

Second Type of Conception.—A view widely removed from the materialistic is clearly presented by two of my correspondents, the one a morphologist, the other a physiologist. "I have always supposed"—thus the morphologist—"that, when considered from the standpoint of introspection, it (psychology) is a part of metaphysics, but when treated experimentally it is a branch of physiology." And the physiologist, after stating that "the application of scientific method to consciousness can go only so far as to explain the workings of the nervous mechanism," continues, "to my mind, there

(115) is beyond this (the above) a true and —wholly distinct psychology—a study of the nature and properties of consciousness independent of the nervous mechanism. The methods of science are applicable to matter and energy, but there is no warrant that they are applicable also to the study of consciousness. Most of the older biologists felt that they are not, and that consciousness must eventually be approached by methods that are extra-scientific, and that have not yet been developed. Such a psychology as this is to be born."

In each of these statements we have, it is to be noted, the recognition of a special branch of inquiry whose proper materials are psychological phenomena, and the denial of the possibility of applying the methods of natural science to these phenomena. Instead of contending, as do the materialists, that physiology can deal adequately with consciousness by studying neural processes, the advocates of this non-naturalistic psychology declare that, in spite of the fact that no such thing as consciousness exists for the natural sciences, we are compelled to admit the existence of psychical as contrasted with physical phenomena, and to grant that they may be studied in some way or other. Most interesting, in this conception of the nature and status of psychology, is the denial that a real science of psychology exists side by side with the physical and the biological sciences.

Third Type of Conception.—In order to present the third and last conception I have chosen, as in the previous instance, to quote from two of my correspondents who hold essentially differing varieties of the same conception. Both writers are physiologists. The one writes, "One has to recognize a fundamental distinction between the subject-matters of psychology and physiology. This is briefly that psychology deals with the subjective, physiology with the objective manifestations of living organisms. If psychology fails to gain insight into the nature of the phenomena of consciousness, qua consciousness, then I conceive that it has failed in its object. Its central object is the psychic, and it is interested in the correlated (objective) organic processes only in so far as these throw light on the conditions of psychical phenomena—on their mode of action—supposing them to have any influence on physical processes or on the nature of the organism, of which consciousness, apparently, is one characteristic property or activity." And again, the other physiologist writes, "I am inclined to divide the processes in living things into two classes, and to distinguish two groups of sciences on that basis. Then I should say that physiology is the science which deals with material and energetic processes in living things, and psychology the science which deals with processes which are not material or energetic, that is, with the conscious processes."


This conception thus expressed evidently demands the development of a science which differs from the biological sciences. But before further considering the three types of conception, I shall offer certain general conclusions to which I have been led by a study of the replies to my questions and by reflection concerning the substance of discussions which I have had with many biologists.

The first of these conclusions is that the majority of American biologists either consciously and avowedly, or without realization of the fact, lack that definite knowledge of psychology which alone could entitle them to au opinion concerning the nature of the subject or its right to existence. This fact is not at all surprising in view of the recency of the introduction of experimental method in the study of consciousness, and the psychologist's regret over the state of affairs well pray change to satisfaction when he hears that almost all of my correspondents disclaimed fitness properly to answer my questions. To me, I must admit, this is the most encouraging result of my inquiry.

Secondly, I am forced to conclude that approximately half of our biologists, assuming that consciousness is a manifestation of energy, contend that there can be no real science of psychology apart from the physiology of the nervous system. The remainder hold that, although much that is commonly called psychology properly belongs to physiology, there is either an existent or a possible science of consciousness wholly independent of physiology. Finally, among the believers in an independent science of psychology there are those who hold that its methods are not those of the natural sciences, and those who believe that there now exists a flourishing science of consciousness whose methods are essentially the same as those employed by the physical and the biological sciences.

In the light of the above results of my investigation of opinion, I conclude that the establishment and promotion of psychology as a science among sciences places upon those who believe in its right to an independent existence the burden of convincing biologists, and natural scientists generally, of the logical and practical validity of their claim. This, I believe, can be accomplished best by works.

It is my contention that the three views of psychology presented in the quotations from my correspondents' replies—not to mention other views which do not happen to be popular with our biologists—are neither equally tenable from the logical standpoint nor equally profitable as working bases for the investigation of psychological phenomena, and I offer as my chief excuse for the publication of this paper the fact that I believe the rapid development of a real science of psychology depends largely upon the whole-hearted and enthusiastic acceptance of some form—of the third type of conception.

(117) I shall now present my chief reasons for this belief. There is nothing original in what I am about to write; I have accepted a certain conception of psychology which is prevalent among psychologists, and I take this opportunity to say so.

My notion of the relation of psychology to the biological sciences will appear in the answers which I have to give to the questions (1) Is the material of psychology essentially different from that of the physical and biological sciences? (2) Are the methods of natural science applicable in the study of consciousness? (3) Are the aims or purposes of psychology the same as those off the physical and biological sciences? and (4) Is the scientific investigation of consciousness, as such, worth while?

Natural science means, I take it, the systematic study of phenomena for the purpose of describing them, correlating then with other phenomena., discovering their laws, and explaining them causally. Each special science deals with a limited group of phenomena, which may conveniently be studied as a group. The grouping, however, is entirely artificial, and we must suppose that with the progress of investigation the special sciences will tend to coalesce, so that finally we shall have a general world science which shall deal with all phenomena of energy—the organic as well as the inorganic. I should like to be permitted throughout this discussion to refer to this composite of the physical and the biological sciences as "physics" in order to contrast it with what I wish to call "psychics." The pertinent question for us with respect to the general science of physics is, Would it include psychology? Many American scientists, perhaps most of them, would answer in the affirmative, and for this very reason it seems to me worth while to set. forth my reasons for believing that however far physics be developed, psychology will ever remain logically independent of it.

Accepting the common-sense view of the world, science regards objects now from the objective, now from the subjective point of view. The objective point of regard or attitude toward things is characteristic of physics; it deals with objects as existent " out there " in space and time and as relatively independent of the observer. The subjective attitude is characteristic of psychics; it deals with objects as existent in, the consciousness of the observer. At the same moment an orange or the activity of a dog may be material of physics and of psychics. The whole world is viewed by the naÔve individual, as well as by the scientist, in these strikingly different ways. We may, if we like, refuse to accept the assumption of the physicist that his point of regard lends itself to scientific inquiry ; and we may similarly deny that the psychological attitude toward objects furnishes a scientific approach to the world, but we

(118) simply can not deny the existence of these two attitudes. Upon those who urge that the one or the other attitude should be ignored by scientists, or that the two should be fused and that things should be studied neither as independent existences nor as consciousness, must rest the duty of so directing the development of science as to provide a knowledge of the world which shall be more valuable than that provided by the physical and the psychical ways of viewing things. Logically it would appear that objects of investigation are neither wholly independent of nor wholly dependent upon the scientist, and that it is therefore profitable to approach them by as many paths—the physical and the psychical are only two of many possibilities—as we can discover. Above all else I am interested in the increase of our knowledge of phenomena—their characteristics, relations, etc. —and I believe that we shall progress most satisfactorily for the present by doing our best to apply the methods of exact science to objects as physically and as psychically existent. If later we discover that either or both of these ways of viewing phenomena are unprofitable we can then turn to other approaches to reality. History indicates that it is not well for the scientist to concentrate his attention upon the task of discovering directly how things really exist. Instead it pays him to be satisfied temporarily with partial views of his objects.

I have answered the first question—Is the material of psychology essentially different from that of the physical and biological sciences?—by saying that it is not, and I have contended that physics and psychics examine the same objects from different points of view and with different attitudes toward their materials. This leads us to inquire, Can objects considered as consciousness be studied by the methods of the natural sciences?

Physics, by observation of its objects under natural and experimentally controlled conditions, strives to gain a description of its materials which is quantitatively accurate, which is verifiable, which forms a basis for the prediction of events, and which explains phenomena by revealing their causal relations. The recognition of these several important points with respect to scientific method raises the following questions concerning the methods of psychology.

Does psychology observe under natural and experimental conditions? Certainly. For fifty years the application of experimentation in the study of consciousness has progressed steadily, and there is no proof that the limit of its usefulness has been reached.

Does it strive for quantitatively accurate descriptions of its objects? We mast reply, that only such descriptions satisfy those experimental psychologists who have made the greatest contributions of fact to their science. It has been said that the psychical

( 119) object can not be measured, that one of its prominent characteristics is its restriction to qualitative, as contrasted with quantitative, investigation; but, inasmuch as we constantly refer to psychological objects as greater or less, it seems that the rareness of accurate measurements in psychology is due rather to the observer's lack of skill than to the nature of his objects. At present it is customary to characterize and stigmatize the data of the psychical sciences as crudely inexact in comparison with those of the physical sciences. Unquestionably this is the case, but I wish to insist that it need not be true, and, further, that the responsibility for this condition of the science rests upon psychologists. We need ingenuity, insight, and persistent effort in order to discover ways of describing our objects with exactitude.

Does psychology present verifiable accounts of its objects? I answer, in essentially the same way as do the natural. sciences, but less satisfactorily because of the inexactness of description; for verifiability depends upon the degree of quantitative accuracy with which an event has been studied as to its immediate characteristics and its relations. In all those regions of psychology which have been investigated with a reasonable degree of thoroughness and accuracy we discover verifiability of observations. I n this respect, then, psychics differs from physics in its present status, not in its possibilities.

But the most important question remains to be answered, Does psychology explain phenomena causally? Not a few students of the psychical sciences seem to think that all causal explanations must come from physics, and that psychology is necessarily teleological instead of causal. With this view I must disagree, for an examination of the aims of both physics and psychics reveals the fact that there are two mediate goals: the accurate description of phenomena, and their explanation in causal terms. I contend that causation is not limited to the physical sciences, but that from the psychological point of view, as— well as from the physical, we observe a series of phenomena in which definite sequences are discoverable, and in terms of this apparently necessary arrangement of our objects we explain them. In physics this uniform relation of phenomena is called physical causation; in psychics it is called psychical causation. It is just as important scientifically from the one point of view as from the other. Comparative psychologists especially need to realize that they are not compelled to turn to physiology for explanations of their phenomena.

To sum up this rather dogmatic discussion of scientific method in psychology, I may say that I can discover no essential difference in the methods of the two groups of sciences which I have chosen

( 120) to designate as physics and psychics. Both are observational, experimental, quantitative, causal in their explanations; both are in process of development, but in degree of development the psychical sciences are inferior to the physical sciences. Certain of the reasons for this state of affairs I shall attempt to indicate later in this paper.

The last two of the four questions concerning the relation of psychology to the biological sciences must be answered summarily.

Above I have stated that the aim of natural science is to give accurate descriptions of its objects, to correlate its phenomena,, to discover their laws, and to explain everything causally. This, it seems to me, is the aim also of psychology. In fact this is the common aim of all the physical and psychical sciences.

Is the scientific investigation of consciousness, as such, worth while? Can we justify our attempts to observe objects from the psychological point of view? This i. the kind of question no real scientist stops to ask after he has once committed himself to the search for truth in some division of science. For he knows full well that our outlook is too limited to enable us to answer such queries wisely. No one of us can justify his researches in the eyes of all men, and fortunately none of us feels it necessary to do so. The study of consciousness is worth while, if we can achieve the goal of science.

The current American psychology of to-day is a dismal mixture of physiology and psychology. No wonder biologists are confused respecting the nature and status of the science; no wonder they question its right to the name science. To me it now appears of first importance that we should deal with psychological objects thoroughly and in a rigorously scientific manner instead of devoting most of our time to premature attempts to correlate physiological and psychological phenomena. Even more distasteful to the natural scientist than the purest of speculative philosophy are these attempts of psychologists to picture the neural processes which parallel, or condition (according to the individual's conception of the relation of body and mind), psychological phenomena. Vague imaginings, mostly, are these "physiological explanations" of consciousness. I could quote ad nauseam from standard text-books of psychology in support of my contention that most of us know neither physiology nor psychology well enough to correlate satisfactorily the results of these sciences. I am deeply interested in physiological psychology, as well ;,, physiology and psychology, but I maintain that at present it is more important for science to advance offer knowledge of bodily and mental processes than to speculate concerning their relations or to try to explain one set of phenomena in terms of the other.

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For psychology and psychologists there are certain urgently important and intensely practical, albeit unpleasant, facts which should be mentioned in connection with this discussion. I refer to the status of psychology in America, and to the reasons for the low esteem in which it is held by our physical scientists. Most scientists, whether they believe in a science of consciousness or not, admit that the present status of the subject is extremely unsatisfactory. As compared with even the newest of the physical sciences it appears crude, vague, inexact, unscientific. It is reasonable, therefore, that those of us who are professionally interested in the subject should seek to discover the causes of this state of affairs.

My study of the situation has led me to the conclusion that there are four preeminently important reasons for the sad plight of psychology.[1] These are: (1) The lack of a generally and unquestioningly accepted body of presuppositions or postulates to serve as a working basis; (2) The lack of strong and research-impelling faith in the value of the aims of psychology and in the possibility of attaining these ends by available scientific methods; (3) the too-prevalent lack among empirical psychologists of thorough training in scientific as contrasted with philosophical method, and (4) The prevalence of poor teaching, and especially of the presentation of psychology as a collection of bizarre phenomena, or as a philosophical discipline instead of as a science similar to the physical sciences in aims and methods. I shall briefly consider each or these four facts—for I am forced to admit that they are facts—with the hope that the frank recognition of undesirable conditions may be the first step toward improvement.

As to presuppositions, it is safe to say that few, if any, sciences are in worse plight than psychology. Progress in physics would cease should the investigator question the independent existence of his objects. Indeed, it takes but a superficial survey of the sciences to convince one that no science can flourish until it has definitely accepted a body of presuppositions, and until it has ceased to question them so far as its practical problems are concerned. We recognize that it is impossible to prove the truth of certain of the physicist's most important assumptions, but we do not on that account contend that his descriptions and explanations of the world of objects and events are valueless.

Psychology can not work without assumptions or presuppositions, and it can not progress rapidly and steadily until a certain group of presuppositions has been definitely and heartily accepted

( 122) by the great mass of its workers. It is not sufficient that an investigator here and there should adopt a working basis and then turn all his attention to the problems of his science. There must be union as a source of strength to the science. The study of the animal mind at this time stands forth as an instructive example of the effects of wrangling over assumptions instead of accepting the best that can he found, and then straightway going to work. Especially pertinent at this point is a paragraph from a class report which was submitted to me recently by a student in an introductory course in comparative psychology. It reads, "A peculiarity of Ďanimal Psychology' is that its expositors are still quarreling about its presuppositions. In most sciences the speculative bases are so widely accepted that workers in them, hearing no din of controversy, suppose those bases to be not speculative at all. For that reason expositors of other sciences may doubt the scientific status of animal psychology.' But it will he as scientific as any of the sciences if ever its workers unite upon a criterion of the presence of consciousness. For the distinguishing mark of a science lies not in the selection of first principles, but in the care, and caution, and precision with which they are applied." I sincerely hope that my teachings are at least partly responsible for this opinion, for I believe that it is the correct view, and I heartily wish that it were held by all psychologists.

The sad truth is that to-day psychology means very different things even to psychologists themselves. Already I have pointed out the fact that our biologists look upon the subject as a part of physiology, as a branch of metaphysics, as a possible science in which the methods of natural science are not applicable, or, as a genuine science of the subjective. Scarcely less divergent are the views of those who are really working in psychology. What can be expected of a subject thus hampered? Surely we may not hope for rapid and consistent progress until we have united whole-heartedly upon a working basis and a definition of the aims of our science.

Only less important than agreement as to presuppositions is the attitude of the psychologist toward his work. As a group we lack that strength of faith in our aims, methods, and ability which alone makes for success in research. We lack enthusiasm; we are divided; we waver in our aims; we mistrust our methods as well as our assumptions; we question the value of every step forward, and, as an inevitable result our subject lags at the very threshold to the kingdom of the sciences. In a startling and illuminating way the biologists believe in their aims and methods. Those who fail because of lack of faith and enthusiasm are the exceptions in this domain. Of the physicists and the chemists the same is true. And of the value

( 123) of this attitude toward one's work what further evidence is needed than the achievements of the physical and biological sciences.

To no small extent, in my opinion, our lack of faith and enthusiasm is due to the third of the conditions mentioned above, namely, our inadequate training for the tasks which we set ourselves. Psychologists generally have not been rigorously trained in the methods of the natural sciences; yet, these methods—definite, precise, exacting—are now recognized by the masters among psychologists as the methods of psychology. Teachers and investigators, no less than students of the subject, come to their tasks—often to the research laboratory of experimental psychology—with keen interest in speculative philosophy and not infrequently with theoretical knowledge of scientific method, but of the practises of the exact sciences many of them know nothing from experience. A host of those of us who are known as psychologists simply do not know how to observe or to experiment with objects either physically or psychologically.[2] I hold that it is absurdly inconsistent for us to expect psychology to develop scientifically so long as the majority of her workers are trained in metaphysics instead of in physics or psychics. Doubtless I should hasten to add that I respect both the methods and the results of speculative philosophy, and that I object merely to the use of the subject as a substitute for science of the naturalistic sort. I am convinced that philosophy does not give the training which the experimental psychologist needs. Surely it is well worth while for us to ponder the fact that every psychologist would give more for a single research student well trained in the physical and biological sciences than for a dozen skilled and able speculative philosophers.

Above I have insisted upon training in physics or biology as a preparation for work in psychology, but I should with equal willingness accept training in any science or sciences of the psychological group were they as highly developed on the side of method as are the physical sciences. The time may come when psychology itself will furnish as satisfactory training in scientific method as can now be gained in the physical sciences. But until that time has come, we should avail ourselves freely of the advantages which the physicists have won and generously place at our disposal.

Finally, I wish to call attention to the fact that the prevalent teaching of psychology is not such as to build up a conception of the

( 124) subject as a science or to develop a strictly scientific attitude toward it. Because of diversity in point of view and vagueness and uncertainty as to aims and methods in the minds of those of us who teach it, psychology is, as a rule, presented to elementary students quite unsystematically and unscientifically. Talk with almost any one who has taken only an introductory course in psychology in a college or normal school and the fact will appear that the subject means to the individual either a curious hodge-podge of more or less bizarre and mysterious phenomena or a study of the brain and certain of its functions! Whether it is worse to consider the subject as the study of hypnotism, thought transference, spiritualistic phenomena, delusions, illusions, and dreams, or as the study of brain processes, I leave it to any one who is interested to decide. For my part, I am content to do everything in my power to replace both of these conceptions of the subject by the one to the exposition of which this paper is devoted. It is indeed a serious admission, that of psychology as the systematic and persistent attempt to describe and explain the facts of consciousness the average student has no notion.

There is something radically wrong, for even an elementary course should give each student a definite idea of the chief characteristics of the materials of psychology, of its aims, of its methods, and of its principal achievements.



  1. It is noteworthy that psychology has a much better status in Europe than in America.
  2. Although the greater part of my own contributions to science have been physiological, I feel that I am entitled by my experience in teaching psychology to include myself among the students of consciousness. Were it not for the fact that during the past nine years I have given one or more introductory courses in general psychology, as well as an elementary course in comparative psychology each year, I should not offer any criticisms of the subject

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