Only with a comprehensive detailed theory of the practical processes which agents engage in prior to successful action can one get a picture of all those junctures at which the mechanism of rationality may be applied, and at which irrationality may therefore occur. Rationality, I argue, is the exercise of normatives, such as believable and desirable, whose function is to control the formation of the stages in practical processes by determining what content and which functions of practical states are allowed into the process. Believable is a functional concept, and for an agent to wield it requires that he possess beliefs or a theory he can justify about which states are goal-functional. Desirable is likewise a functional concept, an...