§ 7. =The Scope of Psychology.=—Science, like the Elephant’s Child in the story, is full of an insatiable curiosity. Just as the physicist reaches out, analysing and measuring, to the farthest limits of the stellar universe, so does the psychologist seek to explore every nook and corner of the world of mind; nay more, he will follow after a mere suspicion of mind; we have seen him trying to psychologise the plants. The result is a vast number of books and monographs and articles on psychology, written by men and women of very different interests, knowledge and training; for science does not advance on an ordered front, but still depends largely on individual initiative. A high authority on the Middle Ages has said that one mortal life would hardly suffice for the reading of a moderate part of mediæval Latin; and the psychologist must recognise, whether with pride or with despair, that one life-time is hardly enough for the mastery of even a single limited field of psychology. The student has to get clear on general principles, and then to resign himself to work intensively upon some special aspect of the subject-matter,—keeping as closely as he may in touch with his fellow-workers, and aiming to see his own labours in a just perspective, but realising that psychology as a whole is beyond his individual compass. Does that sound exaggerated? Let us then attempt a rough classification! We begin with the =psychology of the normal mind=. Under this heading we have to distinguish (1) _human_ psychology. Human psychology may be _general_, the psychology of the adult civilised man, which forms the principal topic of the text-books of psychology; _special_, the psychology of the human mind at some other stage of individual development: infancy, childhood, adolescence, senility; _differential_, the study of the differences between individual minds; or _genetic_, the study of the development of mind from childhood to manhood, and its gradual decay in old age. (2) _Animal_ psychology may be subdivided, in the same way, into general, special, differential and genetic psychology. (3) _Plant_ psychology is still in its first beginnings; but many students are taking the subject seriously. (4) _Comparative_ psychology is the comparative study, either of various types of animal mind, or of the minds of plants, animals and man. It, again, may be general, special or genetic. All these psychologies deal with the _individual_ mind. There is also a _collective_ psychology; and, though its divisions are not yet sharply marked off from one another, we may distinguish (5) _social_ psychology, which includes the study of what is called the social consciousness, and also the scientific study of the products of the collective mind: language, law and custom, myth and religion; (6) _ethnic_ psychology, the differential psychology of nations or races; and (7) _class_ psychology, the differential psychology of classes or professions.