In learning language, children have to acquire not only words and constructions, but also the ability to make inferences about a speaker’s intended meaning. For instance, if in answer to the question, ‘what did you put in the bag?’, the speaker says, ‘I put in a book’, then the hearer infers that the speaker put in only a book, by assuming that the speaker is informative. On a Gricean approach to pragmatics, this implicated meaning – a quantity implicature – involves reasoning about the speaker’s epistemic state. This thesis examines children’s development of implicature understanding. It seeks to address the question of what the relationship is in development between quantity, relevance and manner implicatures; whether word learning by exclusion is a pragmatic forerunner to implicature, or based on a lexical heuristic; and whether reasoning about the speaker’s epistemic state is part of children’s pragmatic competence. This thesis contributes to research in experimental and developmental pragmatics by broadening the focus of investigation to include different types of implicatures, the relationship between them, and the contribution of other aspects of children’s development, including structural language knowledge. It makes the novel comparison of word learning by exclusion with a clearly pragmatic skill – implicatures – and opens an investigation of manner implicatures in development. It also presents new findings suggesting that children’s early competence with quantity implicatures in simple communicative situations belies their ongoing development in more complex ones, particularly where the speaker’s epistemic state is at stake.
I present a series of experiments based on a sentence-to-picture-matching task, with children aged 3 to 7 years. In the first study, I identify a developmental trajectory whereby word learning by exclusion inferences emerge first, followed by ad hoc quantity and relevance, and finally scalar quantity inferences, which reflects their increasing complexity in a Gricean model. Then, I explore cognitive and environmental factors that might be associated with children’s pragmatic skills, and show that structural language knowledge – and, associated with it, socioeconomic status – is a main predictor of their implicature understanding. In the second study, I lay out some predictions for the development of manner implicatures, find similar patterns of understanding in children and adults, and highlight the particular challenges of studying manner implicatures experimentally. Finally, I focus on children’s ability to take into account the speaker’s epistemic state in pragmatic inferencing. While adults do not derive a quantity implicature appropriately when the speaker is ignorant, children tend to persist in deriving implicatures regardless of speaker ignorance, suggesting a continuing challenge of integrating contextual with linguistic information in utterance interpretation.