A recent development, closely related to statistical science, is the social survey. Beginning with the Pittsburg Survey in 1907–1908, the social survey method has been widely adopted in the United States. Its use has been applied to inventories of a specific community, such as a rural district or a small number of city blocks. There is the specific survey of a given social problem, such as housing or poverty. Then there is the survey of an entire industry or a school system. The social survey is one of the most important sources today of sound social thinking. By it, large quantities of social facts are being collected. Urban and rural surveys, specific and general surveys alike, are affording the best bases at the present time for inductive social thinking. Some of these results have been indicated in a preceding chapter upon the contributions of applied sociology. The nature of the classificatory method has already been indicated in this treatise. The Greeks classified the various fields of knowledge under three heads: physics, ethics, and politics. Francis Bacon classified knowledge according to his understanding of mental operations. He divided mental processes into three, namely, feeling, memory, reasoning; and made a corresponding division of knowledge into art, history, and science. Auguste Comte classified the social elements into four groups: the industrial, the esthetic, the scientific, and the philosophical (previsional). His hierarchal classification of the sciences into mathematics, astronomy, physics, chemistry, biology, and sociology has been discussed in an earlier chapter. Guillaume de Greef may be considered the best exponent of the classificatory method. De Greef accepted Comte’s hierarchy of the sciences with its basic principles of decreasing generality and increasing dependence of parts, assented to Spencer’s evolutionary dictum of increasing coherence and heterogeneity, and added his own concept of volitional contractualism. De Greef argued that social progress is characterized by an increasing degree of volitional activity and freedom. This volitionalism is the basis of rational social control. The telic factors, however, are not well developed by de Greef. His social thought rests upon a certain logical but inaccurate classification of the social elements.