The Thomas theorem is a theory of sociology which was formulated in 1928 by William Isaac Thomas and Dorothy Swaine Thomas:
In other words, the interpretation of a situation causes the action. This interpretation is not objective. Actions are affected by subjective perceptions of situations. Whether there even is an objectively correct interpretation is not important for the purposes of helping guide individuals' behavior.
William Isaac Thomas (August 13, 1863 – December 5, 1947) was an American sociologist, understood today as a key figure behind the theory of symbolic interactionism.
Collaborating with Polish sociologist Florian Znaniecki, Thomas developed and influenced the use of empirical methodologies in sociological research and contributed theories to the sociology of migration. Thomas went on to formulate a fundamental principle of sociology, known as the Thomas theorem, whereby he would contend that "if men define situations as real, they are real in their consequences." This microsociological concept served as a theoretical foundation for the field of symbolic interactionism which was developed by Thomas's younger peers—primarily at the University of Chicago.
A self-fulfilling prophecy is a prediction that comes true at least in part as a result of a person's belief or expectation that the prediction would come true. In the phenomena, people tend to act the way they have been expected to in order to make the expectations come true. Self-fulfilling prophecies are an example of the more general phenomenon of positive feedback loops. A self-fulfilling prophecy can have either negative or positive outcomes. Merely applying a label to someone or something can affect the perception of the person/thing and create a self-fulfilling prophecy. Interpersonal communication plays a significant role in establishing these phenomena as well as impacting the labeling process.
American sociologists W. I. Thomas and Dorothy Swaine Thomas were the first Western scholars to investigate this phenomenon. In 1928, they developed the Thomas theorem (also known as the Thomas dictum): "If men define situations as real, they are real in their consequences." Another American sociologist, Robert K. Merton, continued the research, and is credited with coining the term "self-fulfilling prophecy" and popularizing the idea that "a belief or expectation, correct or incorrect, could bring about a desired or expected outcome." The works of philosophers Karl Popper and Alan Gewirth also contributed to the idea.