Formal Methods in Pragmatics

The starting point is the philosopher H. P. Grice's work on speaker meaning (Philosophical Review, 1957). He analyzes the circumstances in which people attribute meaning to one anothers' utterances and concludes that an interpretation represents the intention that a speaker manifests in using an utterance and addressees recognize from attending to the utterance in context.

Now, Grice's attempts at formalizing the content of these intentions (in the William James Lectures for example) appeal to complicated and poorly-motivated assumptions about the dynamics of human deliberation and action (as do similar formalizations by Searle); they make sense only in the context of Grice's program (quixotic on a Chomskyan understanding of linguistic competence) to reduce knowledge of linguistic meaning to the world knowledge we use generally to reason about others' actions and mental states. Nevertheless, well-known computational formalizations of interpretation as intentions by Perrault, Cohen, Allen and others follow Grice's analysis. The result: difficult formalism, implausible inferences and an all-but-unimplementable theory.

On my view, the problem is not the analysis of interpretation as intention; it remains the best analysis we have. Instead, the difficulty comes from the many auxiliary assumptions that are required to make sense of the analysis. But it has now been twenty years since computer scientists first tried to formalize the analysis, and research in the cognitive science of language use offers a range of new insights to draw on:

• Plans and intentions are resources for deliberation and collaboration (Bratman, Pollack, Agre). To fill this role, intentions should distill the real causal dynamics of the world into its abstract, even heuristic, essentials.
• Linguistic structures can be described abstractly but precisely as combinations of independently-meaningful elements assembled by simple primitive operations (Joshi's adjunction, Steedman's combinators, Chomsky's merge). With these descriptions, search through linguistic structures sets up a space of natural choices that can be linked directly to interpretations.
• Linguistic meanings can be described abstractly but precisely as specifications for context change (Kamp, Heim, and many others). These specifications cast utterances as actions by which a speaker makes a relevant contribution to conversation by drawing explicitly and intentionally on information given by the context.
• Language use is a complex collaborative interaction (Clark, Lewis, Brennan). This interaction doesn't just involve signalling and recognizing intentions; it also involves processes such as acknowledgment, grounding, accommodation, clarification, and correction. Interpretations must support collaborative language use, but they can also rely on it and abstract away from it.

In my research, I hypothesize that these ideas can be harmonized, so as to offer a streamlined analysis of communicative intention that defers to, exploits and ties together research in philosophy, linguistics and psychology. Look for the analysis to make it possible to describe phenomena such as entrainment, accommodation, and vagueness, which fall at the intersection of these fields, with a new rigor that complements rather than obscures our intuitions.

At the same time, these ideas open up ways to use the best ideas from computer science to implement pratical dialogue systems with sophisticated competence in language use.

• Representations of interpretations can draw on computational logic - starting with the typed data elements and bound variables of the Curry-Howard isomorphism between propositions and types, and between proofs and programs - to describe inferences about coordinated deliberation, choice and action.
• Characterizations of processes in conversation can appeal to probabilistic and decision-theoretic reasoning about interpretations, and can thereby reconcile high-level specifications of linguistic behavior with empirical facts about people's language use.