In ‘A Coherence Theory of Truth and Knowledge’, Donald Davidson argues that it is not possible for us to be massively mistaken in our beliefs. The argument is based on the possibility of an omniscient interpreter who uses the method of radical interpretation to attribute beliefs, since an omniscient interpreter who uses this method will attribute largely true beliefs to those he is interpreting. In this paper we investigate some of the assumptions behind this argument, and we argue that these assumptions are incompatible with Davidson’s view that the object of a belief is its cause. If Davidson wants to keep his interpretationist theory of mind, he should therefore abandon that view.