The Thomas theorem is a sociological concept formulated by sociologists William I. Thomas and Dorothy Swaine Thomas in 1928. It states that if people define situations as real, those situations have real consequences. This means that individuals' perceptions and beliefs about a situation can influence their actions and the outcomes of that situation, regardless of the objective reality. For example, if a person believes they are in a dangerous environment, they may act defensively, which could escalate tensions, even if the environment is not actually dangerous. The Thomas theorem highlights the importance of subjective interpretation in social interactions and the impact of beliefs on behavior.