This book is a defense of modal realism; the thesis that our world is but one of a plurality of worlds, and that the individuals that inhabit our world are only a few out of all the inhabitants of all the worlds. Lewis argues that the philosophical utility of modal realism is a good reason for believing that it is true.

A very simple contextualist treatment of a sentence containing an epistemic modal, e.g. a might be F, is that it is true iff for all the contextually salient community knows, a is F. It is widely agreed that the simple theory will not work in some cases, but the counterexamples produced so far seem amenable to a more complicated contextualist theory. We argue, however, that no contextualist theory can capture the evaluations speakers naturally make of sentences containing epistemic modals. If (...) we want to respect these evaluations, our best option is a relativist theory of epistemic modals. On a relativist theory, an utterance of a might be F can be true relative to one context of evaluation and false relative to another. We argue that such a theory does better than any rival approach at capturing all the behaviour of epistemic modals. (shrink)

The simplest story about modals—might, must, possibly, necessary, have to, can, ought to, presumably, likelier, and the rest—is also the canon: modals are context-dependent quantifiers over a domain of possibilities. Different flavors of modality correspond to quantification over different domains of possibilities. Logical modalities quantify over all the possibilities there are, physical modalities over possibilities compatible with the..

This volume puts forward a distinct new theory of direct reference, blending insights from both the Fregean and the Russellian traditions, and fitting the general theory of language understanding used by those working on the pragmatics of natural language.

Relativism offers an ingenious way of accommodating most of our intuitions about 'know': the truth-value of sentences containing 'know' is a function of parameters determined by a context of use and a context of assessment. This sort of double-indexing provides a more adequate account of the linguistic data involving 'know' than does standard contextualism. However, relativism has come under recent attack: it supposedly cannot account for the factivity of 'know', and it entails, counterintuitively, that circumstances of evaluation have features that (...) cannot be shifted by any intensional operator. I offer replies to these objections on behalf of the relativist. I then argue that a version of contextualism can account for the same data as relativism without relativizing sentence truth to contexts of assessment. This version of contextualism is thus preferable to relativism on methodological grounds. (shrink)

By “epistemic modals,” I mean epistemic uses of modal words: adverbs like “necessarily,” “possibly,” and “probably,” adjectives like “necessary,” “possible,” and “probable,” and auxiliaries like “might,” “may,” “must,” and “could.” It is hard to say exactly what makes a word modal, or what makes a use of a modal epistemic, without begging the questions that will be our concern below, but some examples should get the idea across. If I say “Goldbach’s conjecture might be true, and it might be false,” (...) I am not endorsing the Cartesian view that God could have made the truths of arithmetic come out differently. I make the claim not because I believe in the metaphysical contingency of mathematics, but because I know that Goldbach’s conjecture has not yet been proved or refuted. Similarly, if I say “Joe can’t be running,” I am not saying that Joe’s constitution prohibits him from running, or that Joe is essentially a non-runner, or that Joe isn’t allowed to run. My basis for making the claim may be nothing more than that I see Joe’s running shoes hanging on a hook. (shrink)

Predicates of personal taste (fun, tasty) and epistemic modals (might, must) share a similar analytical difficulty in determining whose taste or knowledge is being expressed. Accordingly, they have parallel behavior in attitude reports and in a certain kind of disagreement. On the other hand, they differ in how freely they can be linked to a contextually salient individual, with epistemic modals being much more restricted in this respect. I propose an account of both classes using Lasersohn’s (Linguistics and Philosophy 28: (...) 643–686, 2005) “judge” parameter, at the same time arguing for crucial changes to Lasersohn’s view in order to allow the extension to epistemic modals and address empirical problems faced by his account. (shrink)

Epistemic modals are standardly taken to be context-dependent quantifiers over possibilities. Thus sentences containing them get truth-values with respect to both a context and an index. But some insist that this relativization is not relative enough: `might'-claims, they say, only get truth-values with respect to contexts, indices, and—the new wrinkle—points of assessment (hence, CIA). Here we argue against such "relativist" semantics. We begin with a sketch of the motivation for such theories and a generic formulation of them. Then we catalogue (...) central problems that any such theory faces. We end by outlining an alternative story. (shrink)

In this paper I offer an account of the meaning of must and can within the framework of possible worlds semantics. The paper consists of two parts: the first argues for a relative concept of modality underlying modal words like must and can in natural language. I give preliminary definitions of the meaning of these words which are formulated in terms of logical consequence and compatibility, respectively. The second part discusses one kind of insufficiency in the meaning definitions given in (...) the first part, which arise from the ex falso quodlibet paradox of logical consequence. In stepwise fashion, I make an attempt to avoid most of the consequences of this paradox for the meaning definitions of must and can. (shrink)

I think that there are good reasons to adopt a relativist semantics for epistemic modal claims such as ``the treasure might be under the palm tree'', according to which such utterances determine a truth value relative to something finer-grained than just a world (or a <world, time> pair). Anyone who is inclined to relativise truth to more than just worlds and times faces a problem about assertion. It's easy to be puzzled about just what purpose would be served by assertions (...) of this kind, and how to understand what we'd be up to in our use of sentences like ``the treasure might be under the palm tree'', if they have such peculiar truth conditions. After providing a very quick argument to motivate a relativist view of epistemic modals, I bring out and attempt to resolve this problem in making sense of the role of assertions with relativist truth conditions. Solving this problem should be helpful in two ways: first, it eliminates an apparently forceful objection to relativism, and second, spelling out the relativist account of assertion and communication will help to make clear just what the relativist position is, exactly, and why it's interesting. (shrink)