  The possibility of a behaviorally undetectable inversion scenario (P1a) can be motivated by appeal to the sorts of considerations discussed in 2.3.1 above. However, in order to refute functionalism a stronger inversion hypothesis (P1b) is needed. As Block and Fodor point out, functionalism allows us to deny that “two organisms are in the same psychological state whenever their behaviors and/or behavioral dispositions are identical” (1972, 86), hence avoiding the stock objections to behaviorism. The functionalist, then, has no problem with behaviorally undetectable inversions. But why should she concede the possibility of a functionally undetectable inversion? The question can be made more pointed by observing that (a) no one has ever articulated a detailed functionalist theory of any mental state, and (b) any realistic version of such a theory would be extremely  complicated.[31]  In favor of the possibility of a functionally undetectable inversion, Block and Fodor offer its “conceptual coherence”: