One of the central issues in modal metaphysics is whether the reductionof modality is feasible. The most influential reductive theoryin the debate is Lewis's "modal realism," which identifies possibleworlds with maximal spatiotemporally related wholes. Numerous attemptshave been made to argue for or against its plausibility andacceptability. In this paper, we aim to show the impossibility of theLewisian reduction of modality in light of the explanatory power resultingfrom such a reduction. First, a general metametaphysicalbackground of reductive theories of modality is delineated. Second,the explanatory-power-based argument against the possibility of theLewisian reduction is presented, the key being the precise understandingof the power of what is called the "island universes" objection.The discussion enables us to get a clear appreciation of the optionsfor modal theorizing.

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