 Jackson claims that apriori conceptual analysis plays a crucial role in metaphysics (Jackson 1994; 1998a). Metaphysical reductions provide a constitutive account of some target domain (e.g., beliefs, free will, water, moral rightness) in terms of more basic features of the world (e.g., the properties postulated by an idealized physics, ideas in the mind of God, the mosaic of sense data). A physicalist about mental states, for instance, is committed to there being specific facts about the microphysical structure of the world that suffice for the existence of beliefs, desires and sensory experiences. The physicalist is thus committed to metaphysically necessary “entailments” connecting claims about the two domains: it’s metaphysically necessary that if such-and-such physical facts obtain, then such-and-such mental facts obtain. This metaphysical entailment relation can arguably be cashed out in terms of global supervenience (Jackson 1998a, 6–14). [See the entry on  supervenience.]