 If physical predicates stood in strict lawful relations to mental predicates, this contingency would ‘infect’ the mental in the following sense. Suppose that there were strict bridge laws correlating the instantiation of mental and physical properties, ‘P1 ↔ M1’ and ‘P2 ↔ M2’. Then, Kim argues, rational principles of the form ‘M1 →  M2’ would enable the logical derivation of physical laws like ‘P1 → P2’. Indeed, the reverse would be true as well; starting with the physical law ‘P1 → P2’, and assuming the psychophysical bridge laws, one could derive the rational principle ‘M1 → M2’. However, the metaphysical status of the rational principle and the physical law are importantly different—rational principles are necessary, true in all possible worlds, while physical laws, being contingent, are not. In particular, with the bridge laws in place, a contingent physical law could explain (through derivation) the rational principle, undermining its status as necessary. Since it is the bridge laws that enable these troublemaking derivations, they—and thus strict psychophysical laws—are to be rejected. This is how Kim makes sense of Davidson’s suggestive claim that mental anomalism is grounded in the fact that mental and physical explanation owe their allegiance to different sources of evidence. (For related discussion, see the supplement on  Explanatory Epiphenomenalism.)