Andrew McCarthy

This paper develops some modal metatheory for quantified modal logic. In such a theory, the logic of a first-order modal object-language is made sensitive to the modal facts, stated in the metalanguage. This is radically different from possible worlds semantics, which reduces questions of validity to questions of nonmodal set theory. We consider theories which characterize a notion of truth under a second-order interpretation, where an operator for metaphysical necessity is treated homophonically. The form they take is crucially influenced by whether the Barcan formulas are part of the metalogic. The main result is that, with the Barcan formulas, formulating a modal metatheory is easy; principles of classical semantics transfer over smoothly with natural adaptations to the modal setting. Without the Barcan formulas, it seems to be much harder. Several options are considered, but each involves commitments plausibly in tension with the underlying philosophical motivations for rejecting them.

Yagisawa (2005) considers two old arguments against the existence requirement. Both arguments are significantly less appealing than Yagisawa suggests. In particular, the second argument, first given by Kaplan (1989: 498), simply assumes that existence is contingent (§1). Yagisawa’s ‘new’ argument shares this weakness. It also faces a dilemma. Yagisawa must either treat ‘at @’ as a sentential operator occupying the same grammatical position as ‘∼’ or as supplying an extra argument place. In the former case, Yagisawa’s argument faces precisely the problems he concedes that Kaplan’s argument does (§2). In the latter case, though the argument does not face these problems, it renders the sense in which things exist contingently no threat to (E) properly understood (§3).