and of institutions to one another. It is to be criticized as faulty because it fails to emphasize the evolution of those relations. All science is now evolutionary in spirit and in method and believes that things cannot be understood except as they are understood in their genesis and development. It would, therefore, perhaps be more correct to define sociology as the science of the evolution of human interrelations than to define it simply as the science of social organization. The Problems of Sociology.--The problems of sociology fall into two great classes; first, problems of the organization of society, and second, problems of the evolution of society. The problems of the organization of society are problems of the relations of individuals to one another and to institutions. Such problems are, for example, the influence of various elements in the physical environment upon the social organization; or, again, the influence of various elements in human nature upon the social order. These problems are, then, problems of society in a hypothetically stationary condition or at rest. For this reason Comte, the founder of modern sociology, called the division of sociology which deals with such problems _Social Statics_. But the problems which are of most interest and importance in sociology are those of social evolution. Under this head we have the problem of the origin of society in general and also of various forms of association. More important still are the problems of social progress and social retrogression; that is, the causes of the advancement of society to higher and more complex types of social organization and the causes of social decline. The former problem, social progress, is in a peculiar sense the central problem of sociology. The effort of theoretical sociology is to develop a scientific theory of social progress. The study of social evolution, then, that is, social changes of all sorts, as we have emphasized above, is the vital part of sociology; and it is manifest that only a general science of society like sociology is competent to deal with such a problem. Inasmuch as the problems of social evolution are problems of change, development, or movement in society, Comte proposed that this division of sociology be called _Social Dynamics_.