Abstract: Considers the possibility that intrinsic and extrinsic motivation are not independent, that they do not summate, and that a consequence of arousing extrinsic motivation is to reduce intrinsic motivation. The research relating personal causation to the interaction between the types of motivation is reviewed, and empirical evidence is presented. The interaction effects are noted to be symmetrical in some conditions, and the adequacy of current theories of work motivation is questioned. Innovations such as job enlargement, job enrichment, and participative management appear designed to simultaneously manipulate both types of motivation.