 (2′) and (3′) reflect the multiple realizability contention. But there is no mystery in how to reconcile (1)–(3). Append “per week” to (1), “this week” to (2), and “last week” to (3). Similarly, append “per nervous system-type” to (1′), “in human nervous systems” to (2′), and “in mollusk nervous systems” to (3′). Inconsistencies evaporate. Lewis’s point is that identity claims are always specific to a domain. One might wonder whether Lewis’s point generalizes to capture the science fiction examples Putnam hinted at in passing (see  §1.2  above). Lewis was certainly aware of Putnam’s (1967) argument’s reach (Lewis offers this argument as part of a review of the book in which Putnam’s piece first appeared). So we can assume Lewis thought domain-specific reductions generalize to these metaphysically possible cases as well. (See Lewis’s own elaboration of this argument in his 1983.)