Hybrid languages have both modal and first-order characteristics: a Kripke semantics, and explicit variable binding apparatus. This paper motivates the development of hybrid languages, sketches their history, and examines the expressive power of three hybrid binders. We show that all three binders give rise to languages strictly weaker than the corresponding first-order language, that full first-order expressivity can be gained by adding the universal modality, and that all three binders can force the existence of infinite models and have undecidable satisfiability (...) problems. (shrink)

We investigate the expressive power of memory logics. These are modal logics extended with the possibility to store (or remove) the current node of evaluation in (or from) a memory, and to perform membership tests on the current memory. From this perspective, the hybrid logic (↓), for example, can be thought of as a particular case of a memory logic where the memory is an indexed list of elements of the domain.

Kaplan claims in Demonstratives that no operator may manipulate the context of evaluation of natural language indexicals. We show that this is not so. In fact, attitude reports always manipulate a context parameter (or, rather, a context variable). This is shown by (i) the existence of De Se readings of attitude reports in English (which Kaplan has no account for), and (ii) the existence of a variety of indexicals across languages whose point of evaluation can be shifted, but only in (...) attitude reports. We develop an alternative account within an extensional framework with overt quantification over times, worlds and contexts. Various typological facts are discussed, esp. the distinction between English, Amharic and Ewe pronouns, and that between English and Russian tenses. (shrink)

In this paper I assume that syntactic structures contain items that function as variables over possible worlds (or things like possible worlds). I show that in certain syntactic positions we can use some variables but not other. I accordingly motivate a "binding theory" for the items that occupy these positions, and I discuss some consequences of this binding theory.

According to Hans Kamp and Frank Vlach, the two-dimensional tense operators “now” and “then” are ineliminable in quantified tense logic. This is often adduced as an argument against tense logic, and in favor of an extensional account that makes use of explicit quantification over times. The aim of this paper is to defend tense logic against this attack. It shows that “now” and “then” are eliminable in quantified tense logic, provided we endow it with enough quantificational structure. The operators might (...) not be redundant in some other systems of tense logic, but this merely indicates a lack of quantificational resources and does not show any deep-seated inability of tense logic to express claims about time. The paper closes with a brief discussion of the modal analogue of this issue, which concerns the role of the actuality operator in quantified modal logic. (shrink)

Here I propose a coherent way of preserving the identity of material objects with the matter that constitutes them. The presentation is formal, and intended for RSL. An informal presentation is in preliminary draft! -/- Relative-sameness relations—such as being the same person as—are like David Lewis's "counterpart" relations in the following respects: (i) they may hold between objects that aren't identical (I propose), and (ii) there are a multiplicity of them, different ones of which may be variously invoked in different (...) contexts. They differ from counterpart relations, however, in that they are weak equivalence relations (transitive, symmetric and weakly reflexive). The likenesses to counterpart relations make them suitable for an analysis of de-re temporal and modal predications. The difference renders the resulting counterpart theory immune to standard criticisms of Lewis's Counterpart Theory (e.g., in Hazen 1979, and Fara and Williamson 2005). (shrink)

Our thought and talk are situated. They do not take place in a vacuum but always in a context, and they always concern an external situation relative to which they are to be evaluated. Since that is so, François Recanati argues, our linguistic and mental representations alike must be assigned two layers of content: the explicit content, or lekton, is relative and perspectival, while the complete content, which is absolute, involves contextual factors in addition to what is explicitly represented. Far (...) from reducing to the context-independent meaning of the sentence-type or, in the psychological realm, to the 'narrow' content of mental representations, the lekton is a level intermediate between context-invariant meaning and full propositional content. Recognition of that intermediate level is the key to a proper understanding of context-dependence in language and thought. Going beyond the usual discussions of indexicality and unarticulated constituents in the philosophy of language, Recanati turns to the philosophy of mind for decisive arguments in favour of his approach. He shows, first, that the lekton is the notion of content we need if we are to properly understand the relations between perception, memory, and the imagination, and second, that the psychological 'mode' is what determines the situation the lekton is relative to. In this framework he provides a detailed account of de se thought and the first person point of view. In the last part of the book, Recanati discusses the special freedom we have, in discourse and thought, to shift the situation of evaluation. He traces that freedom to a special mode - the anaphoric mode - which enables us to go beyond the egocentric stage of pre-human thought. (shrink)

' I heartily recommend it to any philosopher of language interested in the issues. [] Logicians, of course, will want to savour the whole thing.' Australian Journal of Philosophy, 71:3 (1993).

Hybrid languages are expansions of propositional modal languages which can refer to worlds. The use of strong hybrid languages dates back to at least [Pri67], but recent work has focussed on a more constrained system called $\mathscr{H}$. We show in detail that $\mathscr{H}$ is modally natural. We begin by studying its expressivity, and provide model theoretic characterizations and a syntactic characterization. The key result to emerge is that $\mathscr{H}$ corresponds to the fragment of first-order logic which is invariant for generated (...) submodels. We then show that $\mathscr{H}$ enjoys interpolation, provide counterexamples for its finite variable fragments, and show that weak interpolation holds for the sublanguage $\mathscr{H}$. Finally, we provide complexity results for $\mathscr{H}$ and other fragments and variants, and sharpen known undecidability results for $\mathscr{H}$. (shrink)