General Survey of the Science

The psycho-physics of perception is paralleled by a psycho physics of expression. Mental process finds expression in move ment and in the activity of the glands; and the form of expres, sion, either in itself or in its products admits of precise determina tion. Though little advance has been made in the direct measure ment of the mental state expressed, much has been done in the measurement of the expression, and the results obtained admit of important application. Under this head falls the subject of Mental Tests, and the study of the conditions of efficiency in work. (Cf. INTELLIGENCE TESTS.) The study of mental life in relation to the last phase of the cycle provides Psychology with many points of contact with the anthropological sciences. The mind of primitive man is known only by the products of his work and thought ; and extending the concept of mental product to embrace spoken and written language an enormous field of research is opened up. In this way, for example, Philology and Folklore bring grist to the psychological mill.

Genetic, Comparative, Individual and Abnormal Psy chology.—General Psychology is concerned with what is true of all experiments alike. But experiments differ, and there are many branches of the science concerned with their differences. Some differences are the product of development, and so far as interest is directed to tracing the course of growth, the study is said to be genetic. In one sense all Psychology is genetic, since development is a universal property of mind, and with its develop ment we have been concerned throughout, so far, at any rate, as its course can be reconstructed from the general laws of mental process. But the term "Genetic Psychology" tends to be re stricted to certain special studies; that of the of mind in general, and the inquiry into the course of growth in the individual life. The former has lent a special interest to the study of the animal mind; the latter has fostered the growth of a child Psychology.

Not only do races and species differ, individuals differ too. "Differential" Psychology, or the study of individual differences is one of the fruits of measurement. For one person differs from another not so much in the presence or absence of fundamental characteristics, as in the relative degree to which various common functions may be operative.

Applications of Psychology.

After a long period of slow development the science has reached the stage at which it may be profitably applied. For the purposes of a general survey it will suffice to distinguish formative, directive and curative appli cations. Prominent under the first head are the applications of Psychology to education. In general, educational practice aims at the formation of cognitive, affective and conative dispositions which are likely to be serviceable in later life and in the pursuit of some career; in other words, to develop knowledge and ability, taste and character. Educational Psychology attempts to f ormu late the theory relevant to this process. In many respects, no doubt, the unsystematized "wisdom of the ages" and the genius of the teacher counts for much more than does psychological theory. This is notably the case in the training of taste and char acter. But in regard to the acquisition of knowledge and to the cultivation of ability, Psychology can offer a more effective con tribution. Even here, however, the contributions are largely negative. Theoretical consideration and experimental findings have largely succeeded in dislodging many deeply rooted prac tices based on mistaken doctrines concerning the growth of the mind. The discovery, for example, that training in one direction is not necessarily transferred to others apparently similar has exerted considerable influence upon educational procedure. So, too, has the development of mental tests, the utility of which is by no means limited to the definition of the natural course of development and the limits of educability. If positive and constructive contribution to the training of character are less obvious one can at least point to a promising ferment of ideas in relation to these problems. This has largely been directed and inspired by psychological theory.

Given minds equipped with appropriate dispositions, there is still scope for guidance, for directing energy and ability into appropriate channels and for controlling its economic use. What we have called the directive applications of Psychology are notably illustrated in vocational guidance (q.v.) and by the

study of the conditions of efficiency in work. This field of appli cation is rapidly expanding. It largely depends upon the close co-operation of psychologists and physiologists. The distinctive contribution of the former, however, lies not so much in de tailed application of psychological theory as in providing a new approach to problems hitherto conceived—when conceived at all—in purely physical terms.

The treatment of mental disorder provides another example of the intrusion of the psychological point of view. Mental like bodily function may become deranged, but so-called treatment for both alike had for centuries been conceived in a purely physio logical way. In the later years of the nineteenth century a re action set in against this conception, and methods more psycho logical began to be employed for the treatment of "nervous" disorders. It is too early, perhaps, to pronounce with assurance upon the results of modern psycho-therapy, or to adjudicate between its rival schools, but here, too, there is great promise in the change of standpoint and undoubted value in the ferment of ideas. Not less important than the changes in treatment for mental disorder and the connected preventive and educational applications which advance to this field may be expected to pro vide. (See PSYCHOANALYSIS.) Psychology and Philosophy.—As yet it is not possible to treat Psychology simply as a special science. In view of its dis tinctive concepts it cannot be wholly divorced from philosophical thought. The analysis of these concepts raises fundamental ques tions as to the nature of mind, its causal and other relations to the material world. Special topics may be treated in the em pirical way of the natural sciences without raising metaphysical issues. This is the case, for instance, in the study of the details of sensory experience and of its physical conditions, in the investigation of the laws of learning and of forgetting, and in the quantitative treatment of individual differences. But out side such special inquiries, and more particularly in the attempt to give an account of this science as a whole the Psychologist is continually on the verge of metaphysical issues. To a great extent the successes achieved in the sciences of the material world have had to be paid for by the science of mind. This suc cess has in part been attained by regarding as purely mental all phenomena which fail to fit into the purely physical theory. In this way, for example, the secondary qualities of material things were presented to the Psychologist as examples of what is distinctively "mental" to the consequent confusion of his field. Hypotheses and methods employed in the natural sciences have tended to be regarded as essential to science in general, and to these psychological data are supposed to conform. There has been no purely psychological hypothesis, generally acceptable, which has done for Psychology what the atomic theory, for in stance, has been able to do for Chemistry. Such very wide hypotheses have of ten been proposed, but following physical and chemical models, each sooner or later has become the victim of a reaction. There is thus much to suggest that Psychology must employ hypotheses and methods which are peculiar to itself. In any case the psychologist must be critically occupied with a variety of questions which for other sciences are mainly pre determined. He can escape controversy only by restricting him self to co-operation within the narrow limit of a "school." In the later phases of the history of Psychology, new schools of thought have arisen in almost every decade, each proclaiming a Copernican revolution. Whilst this, no doubt, is evidence of vitality and progress, the multiplicity of claims suggests that the Copernican revolution is yet perhaps to come.

BIBLIOGRAPHY.—General Psychology: G. F. Stout, Manual of Psy chology (4th ed. 1929) and Analytic Psychology (1896) ; W. Mc Dougall, An Outline of Psychology (3rd ed. 1928) ; J. Ward, Psy chological Principles (2nd ed. 192o) ; W. James, Principles of Psy chology (189o) and Text-book of Psychology (1892) ; R. S. Wood worth, Psychology—a Study of Mental Life (1922); Psychologies of 1925 by various authors (1926) ; Traite de Psychologie, ed. by G. Dumas (Paris, 1923). Special Departments: For the more important works on the particular branches of the subject see the bibliographies to the special articles. (G. F. ST.; C. A. MA.)