The analysis of perlocutionary acts is a fundamental component for a theory of human communication which accounts for the response of interactin gsubjects. We introduce two knowledge structures, namely games and contracts, which are used by the mental processes underlying perlocutionary acts. we present our mental processes underlying perlocutionary acts. We present our model through the discussion of an example of game; in particular we focus on the problem of shifting a from the wants of the actor to the wants of the partner.