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The Thomas theorem is a fundamental law of sociology, namely

"If men define situations as real, they are real in their consequences."^[1]

The theorem was formulated by William I. Thomas in his 1928 book The child in America: Behavior problems and programs.

Moreover, W. I. Thomas precisely stated (in 1923) that particularly within every-day-life social worlds any definition of the situation will not only influence the present but - whenever following a series of definitions the individual is involved in - also "gradually a whole life-policy and the personality of the individual himself" ^[2]. Consequently, it was no surprise that W. I. Thomas whenever investigating societal problems like, e.g., intimacy, family, education, basically stressed the rôle of the situation when detecting a social world "in which subjective impressions can be projected on to life and thereby become real to projectors."^[3]

Recently, the Thomas theorem has been attributed to both William I. Thomas and Dorothy Swain Thomas because they both appear as authors on the cover of the book. However, Dorothy Swain Thomas specified in a letter she wrote in 1973 that she was an assistant to William I. Thomas on the paper in question. She went on to say that she was hired at the request of the Rockefeller group to do the book's statistical work, implying that all written text are solely by William I. Thomas. ^[4]

• Nocebo
• Placebo (origins of technical term)
• Self-fulfilling prophecy

1. ↑  The child in America: Behavior problems and programs (New York: Knopf, pp. 571-572).
2. ↑  The Unadjusted Girl. With Cases and Standpoint for Behavioral Analysis N.Y.: Evanston; London: Harper & Row, ³1967: 42)
3. ↑  Social Behavior and Personality. Contribution of W.I.Thomas to Theory and Social Research. Edmond H. Volkart [ed.] N.Y.: Social Research Council, 1951: 14
4. ↑  The Thomas Theorem and The Matthew Effect. Robert K. Merton. Social Forces, December 1995, 74(2):379-424. (Page 401 shows a copy of the letter by Dorothy Swain Thomas.) For more information check http://www.garfield.library.upenn.edu/merton/thomastheorem.pdf - Robert K. Merton on the intellectual history of the Thomas theorem

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