  The third principle is the most contested of the three. It rules out strict laws in psychology; in particular—and most importantly for present concerns—it rules out strict psychophysical laws, that is, laws connecting the mental and physical. According to Davidson, application conditions for mental predicates feature a rationality constraint absent from the application conditions for physical predicates. In ascribing beliefs to others, for instance, we employ a principle of charity that counsels us to make these believers as rational as possible. But this normative constraint has, as Davidson puts it, “no echo” in the physical realm. In this regard, mental and physical predicates are misaligned in a way that precludes strict psychophysical laws.