The special departments of psychology are very numerous, and their interrelations not al ways obvious. We have experimental and physi ological psychology, race or folk or anthropolog ical or ethnic psychology, comparative and genetic, animal and child psychology, social or collective psychology. individual or differential psychology, intro spect ice psychology, abnormal psychology or mental pathology, philosophical and educational or applied psychology. Can we find any guiding principle that shall bring order into this chaos. and exhibit all the psychologies as parts or phases of a unitary whole? We may rule out, first of all. those psychol ogies which are differentiated from the rest, not by diversity of subject-matter or of problem, but by emphasis of method. Experimental psychol ogy, e.g. is merely psychology treated by the experimental method; and since there is, in prin ciple, no mental process or complex of processes that is inaccessible to experiment, experimental psychology may he regarded, in principle. as coextensive with psychology. In other words. it simply an historical accident. the result of the youthfulness of psychological experimentation and of the very natural concernment of the ex perimentalist with the processes that yield them selves most easily to experimental control, that there are some chapters of psychology, as psy chology is written to-day, in which experiment is prominent, and others in which it plays little or no part. So. again. all psychology is intro spective: either directly introspective (normal human psychology) or analogically introspective (infant and animal psychology) : there is no special or peculiar introspective psychology. The phrase is sometimes used to designate a school of thinkers who will hear nothing of the de pendence of mind upon the nervous system. hut seek to elaborate a 'pure' psychology out of nothing but the psyche itself—and are thereby compelled to have recourse to 'unconscious' men tal processes, which are very far from being given in introspection. This use is, however, mis leading: it is better to name the founder of the school, and to speak, e.g. of the Neo-llerbartians.
We may rule out, in the second place. those psychologies that transcend the sphere of mind, whether on the side of science or on that of philosophy. Physiological psychology. e.g. in cludes portions of physiology. The problem of physiological psychology is, to examine those vital processes which lie midway between external and internal experience, and which therefore demand the application, at one and the same time, of the two methods of observation. the external and the internal; and, secondly. from the point of view which it has gained in its in vestigation of these processes, to survey the whole realm of vital phenomena, and thus medi ate. su far as possible, a comprehensive theory of human existence" (Mult, Physio/ogische Pv choloyic. ). Philosophieal psychology, or the philosophy of mind, deals with such questions as that of the nature of mind I whether there is a mind-substance, or whether the mental processes, as given, constitute mental reality: 'substantial ity' us. 'actuality' ) ; of the ultimate elements of mental experience (intellectualism us. voluntar ism): and of the relation of mind to body, of psychical to physical (parallelism us. interac tion). We may mention: Itehroke, Lehr/me/I dr, allYemeimn I'.ycholoyie Ilamburg and Leipzig, 1S94) ; Ladd, Philosophy of Mind (New York, 1;s95) : and Miinsterberg, der PsY chotogic. i. (Leipzig, 1900). Lastly. applied psychology is called upon to furnish regulative principles to the art of education. Genetic psy chology shows how the normal individual de velops; applied psychology has to deduce from the genetic data an ideal plan or scheme of the evolution of personality, and then to show how this ideal may be most nearly attained in prac tice. In the discharge of both offices, it leaves
the ground of scientific psychology.
There still remain the various subdivisions of psychology proper. We shall realize their inter connection and mutual relation most easily hy taking an analogy. Alind, like the living body, is an organism: in this sense. psychology is the correlate of biology. Now biology falls into sev eral part-sciences. The individual living organ ism is. under different aspects. the subject-matter of morphology, of physiology, and of embryology. Morphology treats of the structure of the organ ism. of its composition from cells and from cell aggregates or tissues. Physiology treats of the organism as a group of functions—respiration. secretion. digestion. Enthryology treats of the growth of the organism, structural and func tional alike, following the changes of tissue and of function that mark the rise and fall of the vital processes. Further. biology deals with groups of organisms, with species. Over against morphology stands taxonomy. in which cells and tissues are replaced by organisms and their classes (species, genera, orders, etc.). Over against physiology stands hionomies, which the function of organs within an individual or ganism is replaced by the function of species in the economy of their natural environment. And over against embryology stands paleontology. the ,eienee of the development of species. Once more: biology, as treats of the diseased or defective ol4anisn , and so has its 'abnormal' side.
Let u. apply this ch;ss•tication to psychology.
Ala have, i11 t oiiiu•try tex1-book of psyc•hohlgy. 1. moil hology and a idlysiology of mind. Smile a itlii rs ill strtss upon the analysis of structure tlit:lpe, Tiichener), others upon the a calsis of function (.lames• Stout, Ward) : this i. mainit• a matter of the psychologist's training.
i the direction (scientific or philosophical) from M Rich he approaches the psychological problem. The important thing is to keep the two lines of immir3 distinct, not to hypostatize function, to invent separate struetures that shall carry its st pirate phases, as is done, e.g. by :t psychology that speaks of 'memories' and 'memory ideas' as qualitatively unique processes; and not. to trans late structure directly into function, as is done, e.g. by a psychology that makes sensation the primary source of knowledge. We have. again, in infant. and child psychology, a mental embry ology. Spinoza's classification of the emotions and Wundt's classification of the forms of asso eiation—to bring together instances from In her en t periods of time—are essays in mental tax onomy. Social psychology and ethimpsychology, so far as they have gone, fall fo• the most pla•t under the head of mental bionomics. Animal psychology, and such comparative psychological systems as those of Spencer and Romanes, are the counterparts of paleontology. We may bracket together the study of the child and ani mal minds, of the growth of the individual and racial mind. as genetic psychology. ;Mental path the psychology of the abnormal, deals with such topics as the space ideas of the blind (study of defect or lack), dreaming and hypnosis (tem porary mental derangement), and insanity (per manent mental derangement). Finally, individ nal psychology investigates the variations of normal mental function. The inquiry may be pursued in the interests of genetic psychology (Dalton) o• of mental physiology (Stern). The present quasi-independence of individual psychol ogy is due to the fact that it has hut recently attracted any widespread attention; psychol ogists hay(' peen concerned to discover mental uniformities rather than to examine mental dif ferences. There can lie no doubt that, in course of time, it will he absorbed into general psychol ogy.