On the question of the exact formulation of “the Thomas theorem”

The article attempts to reconstruct the most accurate formulation of the theoretical position, known in sociology as the Thomas theorem. For this purpose, the author outlines the logical structure of the proposition, using set theory as a tool for formal analysis. The content of the concepts included in the Thomas theorem is revealed by referring to the theoretical heritage of W.I. Thomas and reconstructing the meanings that the theorem's author put into the terms used in it. Since the theorem is expressed verbally by its author, the article analyzes the preservation of terms in the transition from the premise (antecedent) to the consequence (consequent). For this purpose, the article offers a series of historical and sociological excursions that reveal the context of the tasks, in which the terms of this theoretical thesis were introduced, such as “situation”, “reality”, “consequences”. On the basis of the formalization of the Thomas theorem and reconstruction of meanings of its concepts, the author offers a detailed and precise formulation.