We have a pervasive tendency to interpret and explain behavior in terms of intentional mental states. We tend, even, to interpret the interaction between animated objects in terms of desires, beliefs, and intentions (Heider and Simmel 1944). This raises the question of when it is appropriate to attribute mental states in the explanation of behavior. According to an instrumentalist stance (Dennett 1987: Ch. 2), the question of when it is appropriate to ascribe mental states cannot be separated fr