Thomas theorem

Persuasion

The Thomas theorem is the sociological principle stated by the Americans William I.

Thomas and Dorothy Swaine Thomas in The Child in America (1928): if people define situations as real, they are real in their consequences. Whether a situation is true matters less than whether it is believed, because belief guides behaviour, and behaviour changes reality. In 1948 the sociologist Robert K. Merton drew from it the concept of the self-fulfilling prophecy, with the example of a sound bank that fails because depositors, convinced otherwise, all rush to withdraw their savings. In crisis communication and in marketing it explains why a perception, positive or negative, has real effects even when the data contradict it, if those data are not communicated well.