 Here we see the interest-relativity of explanation and its bearing on explanatory relevance (see the supplement on  Mental Properties and Causal Relevance)  playing an important role for Davidson. Mental properties must be cited if we want a rational explanation of mental effects. Davidson’s response to epiphenomenalist concerns can thus be described as a kind of ‘dual explananda’ theory of the explanatory role of mental properties. According to this theory, for every (causally interacting) mental event there are two distinct explananda in need of explanation: an event of a certain physical type and an event of a certain mental type. Mental properties are accorded an ineliminable and (given Anomalous Monism) irreducible explanatory role by virtue of their singular capacity to make intelligible the occurrence of other mental properties through the sui generis relation of rationalization. This reflects the point made at the end of  4.3  by the causal definition interpretation of the argument for mental anomalism: that rationality underlies, not mental anomalism, but rather mental realism. (For related discussion of the dual explananda approach, see Macdonalds 1995 and Gibbons 2006.)