The general growth of interest in genetic problems, stimulated so greatly by the work of Darwin, turned the attention of psychologists to the problem of the genesis of the developed human mind,—the problem of its evolution in the race and its development in the individual. Then it at once became apparent that both these processes are essentially social; that they involve, and at every step are determined by, interactions between the individual and his social environment; that, while the growth of the individual mind is moulded by the mental forces of the society in which it grows up, those forces are in turn the products of the interplay of the minds composing the society; that, therefore, we can only understand the life of individuals and the life of societies, if we consider them always in relation to one another. It was realised that each man is an individual only in an incomplete sense; that he is but a unit in a vast system of vital and spiritual forces which, expressing themselves in the form of human societies, are working towards ends which no man can foresee; a unit whose chief function it is to transmit these forces unimpaired, which can change or add to them only in infinitesimal degree, and which, therefore, has but little significance and cannot be accounted for when considered in abstraction from that system. It became clear that the play of this system of forces at any moment of history is predominantly determined by conditions which are themselves the products of an immensely long course of evolution, conditions which have been produced by the mental activities of countless generations and which are but very little modified by the members of society living at any one time; so that, as has been said, society consists of the dead as well as of the living, and the part of the living in determining its life is but insignificant as compared with the part of the dead. Any psychology that recognises these facts and attempts to display the reciprocal influences of the individual and the society in which he plays his part may be called Social Psychology. Collective or Group Psychology is, then, a part of this larger field. It has to study the mental life of societies of all kinds; and such understanding of the group life as it can achieve has then to be used by Social Psychology in rendering more concrete and complete our understanding of the individual life.