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This chapter explores the dialectic of the interaction between modal semantics and modal metaphysics. It begins by looking at three examples of places where semantic and substantive issues interact, and where it is contentious whether a problem calls for a semantic or a metaphysical solution. The first example is an argument from a semantic premise to a metaphysical conclusion that is fallacious; the second is a case of a semantic decision with a metaphysical motivation. The third example is a puzzle where it is controversial whether the puzzle should have a semantic or a metaphysical solution. In this case, it is argued that the metaphysical response is unnecessary—the puzzle is best dissolved on semantic grounds. After discussing these three examples, the chapter considers a specific semantic question about how the quantifiers should work in our modal quantification theory and the way that this question interacts with metaphysical questions about the nature of the modal reality that the language aims to describe. This will lead us to a consideration of more general questions about ontological commitment.

This chapter presents an introduction to David Kaplan. Topics covered include the influence of Church, Carnap, and Montague, from whom Kaplan got the eye for elegant formal codifications; Kaplan's admiration and adoption of the work of the German logician Gottlob Frege as the ground philosophical framework; his most influential work, Demonstratives, which presented his pioneering account of “direct reference” and what is essentially a two‐stage theory of meaning; and his separation of semantics and modal metaphysics.

Epistemologists in general have long agreed that a belief’s being gettiered precludes its being knowledge. However, they have long disagreed on how to understand or explicate that preclusion relation. Of course, some suggestions attract more approval than others do. One of the most commonly favored ones talk, in modal terms, of epistemic safety and epistemic luck. But this chapter argues that such attempted explications fail, because they have not learned enough from the history of modal metaphysics. In particular, epistemologists who reach for such an approach when seeking to understand Gettier cases have unwittingly allowed themselves to be conceiving of such cases in counterpart-theoretic terms, even while deriving a putative result that depends instead on a kind of transworld identity for Gettier cases and for gettiered beliefs. Methodologically, this combination is not viable.

“Actual” and “actually” are fundamental terms of ontology. “Actually p” is logically equivalent to “p” and to “It is true that p”; that is, “p if and only if actually p” is a necessary truth. That is a position taken in this book. During the “modal metaphysics” boom of the 1970s and 1980s, however, it was argued by David Lewis, in ways that commanded great respect, though much less agreement, that the force of “actually p” is not only ontological but more specifically indexical, signifying that p is the case in this world or universe in which we think and speak, but may be false in other worlds that are just as real, but are accessible to us only in imagination. It is argued here, however, that what Lewis offers us is not so much explanations of possibility and actuality, as replacements for them onto which things we commonly say about possibility and actuality can be elegantly mapped. Serious problems for ethics and for inductive reasoning can be raised about such replacements. However, the thesis that everything possible is real, somewhere in the total scheme of things, has a long and honorable history—in Spinoza’s Ethics, for example. Such ideas will be with us in several chapters of this book, and have a major part in the concluding Chapter 11.