The second question, that of the scope of experiment in psychology, has been much dis cussed, and with very different results. If we face it in the light of history, it seems to an swer itself. Psychologists were told, at first, that they could not push the borders of experi ment beyond sensation. But they invaded the spheres of affection and attention. They were then told that expermient was adequate only to the simplest states and processes of mind. But they experimented upon perception and idea, upon association and memory and im agination. They were told again that ex periment could never attain to the purely intellectual, or indeed to any of the higher aspects of the human mind. But they made experiments upon judgment and reasoning, and upon the aesthetic consciousness. It is true that these latter experiments are few and scattered, and that whole consciousnesses still await experimental investigation. But there seems to be no doubt that, in principle, the en tire realm of mind is susceptible to experiment. With a method thus justified, it can only be a matter of time for psychology to establish her self as securely as physics or physiology.
The Various Departments of Psychology. — Many attempts have been made to classify the different departments of psychology in ac cordance with some logical plan. As no such classification has received general acceptance, we may ourselves abandon the attempt to be logical, and simply pass in brief review the most important branches of psychology that exist at the present time.
We may distinguish, at the outset, an ana lytical from a genetic psychology. Defining roughly, we may say that analytical psychology takes the human mind as it is, and aims to dis tribute its elements and laws, while genetic psychology seeks to trace the growth of mind from its first beginnings, and to explain the present in the light of mental history. It is needless to say that the two psychologies over lap at many points. Analysis can seldom be completed, except by help of genetic considera tions; and the study of psychogenesis implies, on its side, an analytical knowledge of the de veloped mind. Genetic psychology is also termed comparative psychology, and has various subdivisions: animal psychology, child psychol ogy, the psychology of adolescence, etc.
We may distinguish, secondly, between quilitative and quantitative standpoints within psychology. Suppose, for example, that I am interested to determine the least difference be tween two weights that can be perceived by the lifting hand. The numerical result that I obtain is a quanti tau e result in analytical psy chology. If, however, I attt Inpt to trace out the various factor- that contribute to my judgment or cbrierence or no-difference, factors of expectation, of habit, of fatigue, of attention, that may affect the of fac tors of attentive comparison, of association, of first impression, of effort or ease, that may directly prompt the judgment,— then I am per forming a qualitative experiment. The two
sorts of result should always go side by side, and should (in a perfect psychology) run ex actly parallel,— a numerical statement accom panying the introduction of every qualitative term. Both are indispensable to complete knowledge. Genetic psychology is, at present, almost entirely qualitative, and will probably remain so for a considerable period. It is but the other day that statistical methods were in troduced into the study of organic evolution.
We may distinguish, once more, between psychology as a science of mental function and psychology as a science of mental structure. The difference is very much like that which obtains between anatomy and physiology. Structural psychology seeks to discover what consciousness is composed of, when the organ ism is functioning in a certain way. I remem ber, or I recognize, or I imagine. What, then, are the constituent processes of the memory consciousness? What is my mind made up of, when I am recognizing? What actually takes place mentally, when I imagine? Many inter esting facts have been brought to light by structural psychology. Thus it has been shown that, when we recognize an object, we ordi narily do so, not by way of a comparison of the perceived thing with its memory image, but simply by way of a diffused "feeling of famil iarity," consisting essentially of those organic (internal) sensations which enter into the bod ily attitude of relief or freedom from tension. Functional psychology seeks, in its turn, to classify and derive the functions of conscious ness, the uses to which mind is put in the service of the organism. Thus it may reduce the root-functions of mind to those of cogni tion and interest, and trace the differentiation of the former into discrimination, integration, comparison, etc., and that of the latter into the manifold modes of conative (will) and emotive consciousness.
All these psychologies are,.in one sense of the term, individual psychologies; they discuss the composition or genesis of a single, typical mind. There is, however, a specific, individual or differential psychology, whose problem it is to trace the correlation between the processes or functions characteristic of a certain type of mind, and to compare this with other minds of different types. Thus it is a fact of individual psychology, in this sense, that some minds de pend mainly upon visual, other again upon auditory, and still others upon kinzsthetie (motor) images in the processes of memory, imagination and thought. Over against indi vidual psychology, in this meaning of the word, stands national or racial psychology, which at tempts to discover the forms of thought and feeling characteristic of the common mind of a people.