Stalnaker on the Interaction of Modality with Quantification and Identity

Abstract

Abstract Logic is sometimes conceived as metaphysically neutral, so that nothing controversial in metaphysics is logically valid. That conception devastates logic. Just about every putative principle of logic has been contested on metaphysical grounds. According to some, future contingencies violate the law of excluded middle; according to others, the set of all sets that are not members of themselves makes a contradiction true. Even the structural principle that chaining together valid arguments yields a valid argument has been rejected in response to sorites paradoxes. In each case, a deviant metaphysics corresponds to the deviant logic. Of course, if one is trying to persuade deviant metaphysicians of the error of their ways, one is unlikely to get far by relying on logical principles that they reject. But that obvious dialectical exigency stably marks out no realm of logic. Each logical principle has persuasive force in some dialectical contexts and not in others.