This paper takes issue with an influential interpretationist argument for physicalism about intentionality based on the possibility of radical interpretation. A core commitment of physicalism is that the intentional truths—about what an arbitrary agent believes, desires, and means—supervene on the physical truths—those truths that are stateable in the terms of an ideal and complete physical theory. The interpretationist claims that we can get a handle on the supervenience of the intentional on the physical by considering the predicament of a radical interpreter, an ideally rational being who knows the physical truths and who sets out to deduce the intentional truths about an arbitrary subject without recourse to any further empirical information. If radical interpretation is possible, the interpretationist argues, there is an a priori entailment from the physical truths to the intentional truths, and the latter supervene on the former.


One of the most compelling arguments for the possibility of radical interpretation, associated most closely with David Lewis and Donald Davidson, gives a central role to decision theoretic representation theorems, which demonstrate that if an agent’s preferences satisfy certain constraints, it is possible to deduce probability and utility functions that represent her beliefs and desires. We argue that an interpretationist who wants to rely on the existing representation theorems in defense of the possibility of radical interpretation faces a trilemma, since for all these theorems, at least one of the following is true:

1. The theorems impose constraints on preference that are both too normatively and psychologically demanding, and hence do not come close to being satisfied even by perfectly rational agents, let alone ordinary ones;

2. The frameworks within which the theorems are proven contain objects the preference ranking of which the interpreter could not know on the basis of knowledge of the physical truths alone;

3. The theorems fail to deliver coherent comparative belief rankings derived from the agents’ preferences.