A developing neurobiological/psychological theory of positive motivation gives a key causal role to reward events in the brain which can be directly activated by electrical stimulation (ESB). In its strongest form, this Reward Event Theory (RET) claims that all positive motivation, primary and learned, is functionally dependent on these reward events. Some of the empirical evidence is reviewed which either supports or challenges RET. The paper examines the implications of RET for the concepts of 'motivation', 'desire' and 'reward' or 'pleasure'. (...) It is argued (1) that a 'causal base' as opposed to a functional' concept of motivation has theoretical advantages; (2) that a causal distinction between the focus' and the 'anchor' of desire suggests an ineliminable 'opacity' of desire; and (3) that some affective concept, such as 'pleasure', should play a key role in psychological explanation, distinct from that of motivational (or cognitive) concepts. A concept of 'reward' or 'pleasure' as intrinsically positive affect is defended, and contrasted with the more 'operational' definitions of 'reward' in some of the hypotheses of Roy Wise. (shrink)