In all important respects, extinction following classical conditioning and following instrumental training appears to be the same general phenomenon, and there has thus far been no need to construct any “two-factor” theories of extinction.16 Considering the differences between the two situations, it is somewhat surprising that this is so. If, for example, classical conditioning is basically an association of two stimuli, and the instrumental procedure is one which generates an association of a response and a stimulus (that is, the reinforcer), we might expect different effects, different important parameters, different functional relations to obtain in the two case when we break the correlation between the paired terms. This is not the case. The same kinds of effects seem to be found in extinction following both procedures.