660 THE AMERICAN JOURNAL OF SOCIOLOGY
need of the sociologist's studying social psychology is simply the need of developing his own science. Sociology cannot hope to become a well-organized and perfected discipline until it has, for a part of its foundation at least, a fully developed social psychology.
One particular respect may here be pointed out in which social psychology can aid in the construction of a general soci- ology. When conceived as social philosophy, it is evident that sociology in its genetic aspect may be regarded as the philosophy of history. Now, social psychology in its genetic aspect has also to do with the problem of a philosophy of history on its sub- jective side. Group psychical processes are the historical pro- cesses on their subjective side par excellence. When the genetic aspect of social psychology is fully worked out, therefore, it should yield a philosophy of history. Without entering upon any discussion of the difficulties of such a discipline, we would merely remark that such a subjective interpretation of historical processes would seem possible, if any interpretation is. If the psychical factor is the unifying, life-preserving, and life-devel- oping factor in the group, it would seem that, if any philosophy of history whatever is attainable, it must be reached through the interpretation of the psychical process of societary develop- ment, that is, through the explanation of the process of growth of what we may, for want of a better term, call the " social mind." Such a subjective philosophy of history, however, would undoubt- edly need supplementing by reference to those physical facts which constantly affect the process of social growth ; and such a supplementing it would be the duty of sociology to furnish in its complete interpretation of the historico-genetic process of societies.
If the study of social psychology may be regarded as neces- sary to the further development of sociology, it is hardly of less importance for the special social sciences. Even that social science which from its nature is most bound by the facts of the physical world, namely, economics, would be greatly helped by the development of social psychology. Within the last twenty years economic thinkers have come to look more and more to
