It is practically an article of faith in psychology that in order to do empirical research one must first operationally define one's variables. However, the 'operational attitude', first advocated by the physicist Percy Bridgman in the 1920s, has since been rejected by virtually every serious philosopher of science as unworkable. Furthermore. 'operationism' -- as developed by psychologists in the 1930s and 1940s -- was based on a misunderstanding of Bridgman's intent from the outset. Nevertheless, contemporary textbooks continue to extol the (...) virtues of operational definitions and today's psychology students are still required to learn the strategy. This paper discusses the historical background of operationism, its transmission from physics to psychology and the reasons for its continued tenacity in the face of repeated refutations and Bridgman's own repudiation in the 1950s. (shrink)