5. A sociological definition of the city must recognize that such a complex phenomenon cannot be adequately characterized in terms of any one single distinguishing mark or any set of formal and arbitrary characteristics. The city is, to be sure, a human group occupying a definite area, with a set of technical devices, institutions, administrative machinery, and organization which distinguish it from other groupings. But in this conglomeration of buildings, streets, and people the sociologist discovers a psychophysical mechanism. For him the city is a set of practices, of common habits, sentiments and traditions which have grown up through several generations of life and are characteristic of a typical cultural unit. Within this larger entity which is called the city he sees many other groupings of people and areas which are the result of growth and of a continuous process of sifting and allocation, each one of which areas has a character of its own and produces its special type of inhabitant. He sees a number of occupational and cultural groups whose interests and characteristics mark them off one from the other, but who, nevertheless, are conscious of their membership in some common larger group known as the city, and who participate in its life. From another point of view the city is an institution which has arisen and maintains itself to some extent independently of the population because it satisfies certain fundamental wants, not only of the local inhabitants, but also of a larger area which has become dependent upon what the city has to give. The city, finally, may be regarded as the product of three fundamental processes: the ecological, the economic, and the cultural, which operate in the urban area to produce groupings and behavior which distinguish that area from its rural periphery. Izoulet, Jean. _La Cité moderne et la métaphysique de la sociologie_ (_Paris_, 1894). Maunier, René. “The Definition of the City.” Translated by L. L. Bernard, _Amer. Jour. Sociol._, XV, 536–48. A critical examination of the existing definitions of the city in the light of sociological theory. (I, 1, 2, 3, 4.) Almost every textbook in the field of sociology has some sort of a working definition of the city. In addition there are available the various conceptions of the city underlying the social surveys. II. THE NATURAL HISTORY OF THE CITY The history of the city is almost synonymous with the history of civilization. The sociologist is interested in the natural history of the city as a phase of social evolution. Unlike the historian, he is not aiming to get the concrete facts of the rise and the decay of any particular city, but rather seeks to find in the study of the history of various cities the genesis of the typical city as a basis for the classification of types of cities and of social processes, irrespective of time and place.