 Behaviorism dominated American psychology in the early part of the 20th century, beginning with Thorndike's (1911) experiments on animals learning by trial and error to escape from the “puzzle boxes” that he had constructed. But even Thorndike's famous “law of effect” refers to the animal's “satisfaction or discomfort” (1911, p.244). It was with the radical anti-mentalism of John B. Watson (1928) and B.F. Skinner (1953), both of whom strongly rejected any attempts to explain animal behavior in terms of unobservable mental states, that American psychology became the science of behavior rather than, as the dictionary would have it, the science of mind and behavior. 