W. I. Thomas

W. I. Thomas was an American sociologist and a founding figure of the Chicago School whose work helped establish the empirical study of immigration, social disorganization, and the definition of the situation in American sociology. With Florian Znaniecki, he co-authored The Polish Peasant in Europe and America (1918 to 1920), a pioneering study that used personal letters, diaries, and other life-history documents to analyze how Polish immigrants and their families adapted to social change across two continents. Thomas is best remembered for the Thomas theorem, the principle that if people define situations as real, those situations become real in their consequences, a formulation that became a foundational statement of the idea that subjective interpretation shapes social outcomes.