Daniel Lassiter

Vagueness as probabilistic linguistic knowledge

Consideration of the metalinguistic effects of utterances involving vague terms has led Barker [1] to treat vagueness using a modified Stalnakerian model of assertion. I present a sorites-like puzzle for factual beliefs in the standard Stalnakerian model [28] and show that it can be resolved by enriching the model to make use of probabilistic belief spaces. An analogous problem arises for metalinguistic information in Barkers model, and I suggest that a similar enrichment is needed here as well. The result is a probabilistic theory of linguistic representation that retains a classical metalanguage but avoids the undesirable divorce between meaning and use inherent in the epistemic theory [34]. I also show that the probabilistic approach provides a plausible account of the sorites paradox and higher-order vagueness and that it fares well empirically and conceptually in comparison to leading competitors.

Embedded Implicatures as Pragmatic Inferences under Compositional Lexical Uncertainty

How do comprehenders reason about pragmatically ambiguous scalar terms like some in complex syntactic contexts? In many pragmatic theories of conversational implicature, local exhaustification of such terms (‘only some’) is predicted to be difficult or impossible if the result does not entail the literal meaning, whereas grammatical accounts predict such construals to be robustly available. Recent experimental evidence supports the salience of these local enrichments, but the grammatical theories that have been argued to account for this evidence do not provide explicit mechanisms for weighting such construals against others. We propose a probabilistic model that combines previous work on pragmatic inference under ‘lexical uncertainty’ with a more detailed model of compositional semantics. We show that this model makes accurate predictions about new experimental data on embedded implicatures in both non-monotonic and downward-entailing semantic contexts. In addition, the model’s predictions can be improved by the incorporation of neo-Gricean hypotheses about lexical alternatives. This work thus contributes to a synthesis of grammatical and probabilistic views on pragmatic inference.

Epistemic Comparison, Models of Uncertainty, and the Disjunction Puzzle

The best known theory of modality in linguistics (Kratzer 1991, 2012) uses a binary relation on worlds to state truth-conditions for sentences with epistemic auxiliaries, and lifts this order to an order on propositions to state meanings for epistemic comparatives and equatives with likely and probable. It has recently been observed that this theory makes incorrect predictions about the truth-conditions of epistemic comparative and equative sentences in interaction with disjunction. I analyze the source of this problem in Kratzer’s and several related theories, and consider several modifications suggested in the recent literature. All of the theories available either fail to resolve the problem, or generate incorrect predictions about the relationship between must and likely when combined with Kratzer’s semantics for the auxiliaries. Various alternative models of uncertainty are available which can be used as a semantics for likely and do not encounter the semantic problems discussed here. In particular, qualitative and numerical probability have the necessary features, as do several weaker approaches that include probability as a special case. Data involving entailments and degree modification are argued to provide a reason for preferring the probabilistic approach. I then consider several methods of integrating this approach with Kratzer’s semantics for the epistemic auxiliaries, showing that all of them wrongly invalidate the inference from must to (much) more likely than not. I conclude by stating three alternative semantics for the auxiliaries which do better, one quantificational and two probabilistic. The choice between them will depend on the resolution of three open problems involving the meanings of the auxiliaries which are detailed in the concluding section.

The algebraic structure of amounts: evidence from comparatives

Heim [9] notes certain restrictions on quantifier intervention in comparatives and proposes an LF-constraint to account for this. I show that these restrictions are identical to constraints on intervention in wh-questions widely discussed under the heading of weak islands. I also show that Heims proposal is too restrictive: existential quantifiers can intervene. Both of these facts follow from the algebraic semantic theory of weak islands in Szabolcsi & Zwarts [25], which assigns different algebraic structures to amounts and counting expressions. This theory also makes novel predictions about the interaction of degree operators with conjunction and disjunction, which I show to be correct. Issues involving modal interveners [9], interval semantics for degrees [23,1], and density [4] are also considered.

New Directions in Logic, Language and Computation

In this paper we present a continual context-sensitive abductive framework for understanding situated spoken natural dialogue. The framework builds up and refines a set of partial defeasible explanations of the spoken input, trying to infer the speaker’s intention. These partial explanations are conditioned on the eventual verification of the knowledge gaps they contain. This verification is done by executing test actions, thereby going beyond the initial context. The approach is illustrated by an example set in the context of human-robot interaction.