Pragmatic Reasoning and Semantic Convention: A Case Study on Gradable Adjectives

Ming Xiang, Christopher Kennedy, Weijie Xu and Timothy Leffel

Gradable adjectives denote properties that are relativized to contextual thresholds of application: how long an object must be in order to count as long in a context of utterance depends on what the threshold is in that context. But thresholds are variable across contexts and adjectives, and are in general uncertain. This leads to two questions about the meanings of gradable adjectives in particular contexts of utterance: what truth conditions are they understood to introduce, and what information are they taken to communicate? In this paper, we consider two kinds of answers to these questions, one from semantic theory, and one from Bayesian pragmatics, and assess them relative to human judgments about truth and communicated information. Our findings indicate that Bayesian accounts can model human judgments about what is communicated better than they can model human judgments about truth conditions, but the performance improves if the Bayesian approach is supplemented with the threshold conventions postulated by semantic theory.