Every social group tends to create, from the individuals that compose it, its own type of character, and the characters thus formed become component parts of the social structure in which they are incorporated. All the problems of social life are thus problems of the individual; and all problems of the individual are at the same time problems of the group. This point of view is already recognized in preventive medicine, and to some extent in psychiatry. It is not yet adequately recognized in the technique of social case work. Further advance in the application of social principles to social practice awaits a more thoroughgoing study of the problems, systematic social research, and an experimental social science. REPRESENTATIVE WORKS IN SYSTEMATIC SOCIOLOGY AND METHODS OF SOCIOLOGICAL RESEARCH I. THE SCIENCE OF PROGRESS (1) Comte, Auguste. _Cours de philosophie positive_, 5th ed. 6 vols. Paris, 1892. (2) ----. _Positive Philosophy._ Translated by Harriet Martineau, 3d ed. London, 1893. (3) Spencer, Herbert. _Principles of Sociology._ 3d ed. 3 vols. New York, 1906. (4) Schaeffle, Albert. _Bau und Leben des socialen Körpers._ 2d ed., 2 vols. Tuebingen, 1896. (5) Lilienfeld, Paul von. _Gedanken über die Socialwissenschaft der Zukunft._ 5 vols. Mitau, 1873-81. (6) Ward, Lester F. _Dynamic Sociology._ 2 vols. New York, 1883. (7) De Greef, Guillaume. _Introduction à la sociologie._ 3 vols. Paris, 1886. (8) Worms, René. _Organisme et société._ Paris, 1896. II. THE SCHOOLS A. _Realists_ (1) Ratzenhofer, Gustav. _Die sociologische Erkenntnis._ Leipzig, 1898. (2) Small, Albion W. _General Sociology._ Chicago, 1905. (3) Durkheim, Émile. _De la Division du travail social._ Paris, 1893. (4) Simmel, Georg. _Soziologie._ Untersuchungen über die Formen der Vergesellschaftung. Leipzig, 1908. (5) Cooley, Charles Horton. _Social Organization._ A study of the larger mind. New York, 1909. (6) Ellwood, Charles A. _Sociology and Its Psychological Aspects._ New York and London, 1912. B. _Nominalists_ (1) Tarde, Gabriel. _Les Lois de l'imitation._ Paris, 1895. (2) Giddings, Franklin H. _The Principles of Sociology._ New York, 1896. (3) Ross, Edward Alsworth. _The Principles of Sociology._ New York, 1920. C. _Collective Behavior_ (1) Le Bon, Gustave. _The Crowd._ A study of the popular mind. New York, 1903. (2) Sighele, Scipio. _Psychologie des sectes._ Paris, 1898. (3) Tarde, Gabriel. _L'Opinion et la foule._ Paris, 1901. (4) McDougall, William. _The Group Mind._ Cambridge, 1920. (5) Vincent, George E. _The Social Mind and Education._ New York, 1897. III. METHODS OF SOCIOLOGICAL INVESTIGATION A. _Critical Observation on Methods of Research_ (1) Small, Albion W. _The Meaning of Social Science._ Chicago, 1910. (2) Durkheim, Émile. _Les Règles de la méthode sociologique._ Paris, 1904. (3) Thomas, W. I., and Znaniecki, F. _The Polish Peasant in Europe and America._ "Methodological Note," I, 1-86. 5 vols. Boston, 1918-20.