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 from the question of when it is appropriate to ascribe agency, and both questions are to be answered in terms of predictive success: it is appropriate to attribute mental states in the explanation of agency when doing so supports successful predictions of behavior. However, most proponents of the standard theory presume some form of realism, according to which the ascription of mental states is appropriate only if the agent in question possesses the right internal states with the right representational contents. The question of what the possession of representational mental states consists in is one of the most controversial questions in the philosophy of mind and cognitive science, and it is clearly beyond the scope of this entry (see the entries on mental representation and cognitive science). Consider, though, the following remarks. Davidson (1982) held the view that only human agents have the relevant mental attitudes, because he thought that having such attitudes requires linguistic competence. Others have argued that we are justified in ascribing representational mental states to non-human agents if doing so provides the best explanation of their behavior (Allen and Bekoff 1997, for instance). Sometimes it is rather difficult to decide whether or not the best explanation of an agent’s behavior requires the ascription of representational mental states. Sterelny (2001: Ch. 11, 12), for instance, has argued that plausible explanations in terms of desires can sometimes be replaced by equally good explanations in terms of drives. The ascription of a desire is usually construed as the ascription of a representational mental state, whereas a drive can be construed in terms of more basic mechanisms (and without the ascription of representational content). What is important to bear in mind, here, is that the issue concerns not only the possession of the relevant mental states and events. It concerns, moreover, the capacity to combine or process the contents of such attitudes in rational inferences: the capacity to treat the relevant contents as premises in practical reasoning (as emphasized by Anscombe 1957 and Davidson 1970).