 Thus, even if two theories instantiate a relation of the sort required by Nagel’s model, we should not speak of proper reduction, if as a matter of epistemic possibility the connection between the domains of the two theories remains too loose to support the materialist claims. Levine (1993) gives this an epistemological interpretation; Chalmers (1996) seems to suggest that the epistemic possibility of two concepts coming apart implies that there is a metaphysical possibility of the two properties coming apart. Many (e.g., Block &amp; Stalnaker 1999; Van Gulick 1999; Yablo 1999) have criticized this view. Even a hard-core physicalist will deny that the postulation of a mind-brain identity as a brute fact would suffice for reduction, but at the same time accept that it would suffice for the relevant sort of derivation. However, this does not support the further claim that there must be a conceptual path from concepts or predicates of the reducing science to concepts or predicates of the reduced science. Explanations are not an all-or-nothing affair; there might be explanations that are more than mere brute-fact postulates, but still less than the tight conceptual connections required by those who demand an a priori link between the reduced and the reducing science or conceptual framework (Van Gulick 1992; Kim 1998).