 Fodor gave reductionists the best-known account of reduction at that time, the one at work in Paul Oppenheim and Hilary Putnam’s (1958; Fodor subtitles his 1974 as “The Disunity of Science as a Working Hypothesis”) and culminating in Ernest Nagel’s (1961) “derivability” account of intertheoretic reduction. According to Fodor, this “classic” account “connects” disparate elements of the reduced and reducing theories’ vocabularies by way of “bridge laws” (not Nagel’s term!) and claims a reduction when the laws of the reduced theory are derived from the laws of the reducing theory plus the bridge laws. According to Fodor (1974), if reductionism is to establish physicalism, these cross-theoretic bridge laws must assert (contingent) identities of reduced and reducing kinds. But given multiple realizability, the only way this can obtain is if the physical science constituent of a psychophysical bridge law is a disjunction of all the terms denoting possible physical realizations of the mental kind. Given the extent and variety of actual (not to say possible) physical realizations, Fodor insists that it is overwhelmingly likely that the disjunctive component will not be a kind-predicate of any specific physical science. It is also overwhelmingly likely that the disjunctive component will not appear in any genuine law of some specific physical science. Multiple realizability thus demonstrates that the additional requirement imposed by reductionism, beyond that of token physicalism, is empirically untenable. (For a recent argument that multiple realization is consistent with Oppenheim and Putnam’s unity of science via reductions, see Shapiro 2018)