Psychology is unique among the sciences in its joint concern with dual worlds: (a) internal world of feeling and thought, and (b) external world of stimulus and response. The first major movement in psychology, the introspectionist movement of the late 1800s, took the inviting direct attack of studying the internal world with conscious report. Introspective methods, however, led to disarray. They were replaced by an intolerant behaviorism that allowed only observables of the external world. Many important results were thus obtained as with animal conditioning and rote learning.Psychology is unique among the sciences in its joint concern with dual worlds: (a) internal world of feeling and thought, and (b) external world of stimulus and respo...