 Davidson’s denial of the existence of any strict ‘psycho-physical’ laws follows from his view of the mental as constrained by quite general principles of rationality that do not apply, at least not in the same way, to physical descriptions: normative considerations of overall consistency and coherence, for instance, constrain our own thinking about events as physically described, but they have no purchase on physical events as such. This does not mean, of course, that there are no correlations whatsoever to be discerned between the mental and the physical, but it does mean that the correlations that can be discerned cannot be rendered in the precise, explicit and exceptionless form – in the form, that is, of strict laws – that would be required in order to achieve any reduction of mental to physical descriptions. The lack of strict laws covering events under mental descriptions is thus an insuperable barrier to any attempt to bring the mental within the framework of unified physical science. However, while the mental is not reducible to the physical, every mental event can be paired with some physical event – that is, every mental description of an event can be paired with a physical description of the very same event. This leads Davidson to speak of the mental as ‘supervening’ on the physical in a way that implies a certain dependence of mental predicates on physical predicates: predicate p supervenes on a set of predicates S ‘if and only if p does not distinguish any entities that cannot be distinguished by S’ (see ‘Thinking Causes’ [1993]). Put more simply, events that cannot be distinguished under some physical description cannot be distinguished under a mental description either.