Originally used to refer to a mental viewing, a vision, the word theory has come to have diverse meanings, leading Merton (1968) to assert that the "use of the word often obscures rather than creates understanding" (p. 39). Introducing a symposium devoted to the explication of the structure of scientific theories, Suppe (l977b) observed that "philosophers of science still are searching for an analysis of theories which will provide an adequate philosophical understanding of theories" (p. 233).