Finding modal force

This dissertation investigates when and how children figure out the force of modals, that is, when and how they learn that can/might express possibility, whereas must/have to express necessity. Learning modal force raises a logical “Subset Problem”: given that necessity entails possibility, what prevents learners from hypothesizing possibility meanings for necessity modals? Three main solutions to other Subset Problems have been proposed in the literature. The first is a bias towards strong (here, necessity) meanings, in the spirit of Berwick (1985). The second is a reliance on downward-entailing environments, which reverse patterns of entailment (Gualmini & Schwarz, 2009). The third is a reliance on pragmatic situational cues stemming from the conversational context in which modals are used (Dieuleveut et al., 2019). This dissertation assesses the viability of each, by examining the modals used in speech to and by 2-year-old English children, through a combination of corpus studies and experiments testing the guessability of modal force based on their context of use. I show that negative and other downward-entailing contexts are rare with necessity modals, making them impractical on their own. However, the conversational context in which modals are used in speech to children is highly informative about both forces. Thus, if learners are sensitive to these conversational cues, they, in principle, do not need to rely either on a necessity bias nor on negative environments to solve the Subset Problem. Turning to children’s own productions, I show that children master possibility modals very early: by age 2, they use them productively, and in an adult-like way. However, they struggle with necessity modals: they use them less frequently, and not in an adult-like way. Their modal uses show no evidence for a necessity bias. To assess how children actually figure out modal force, and which of the available cues children use to figure out modal force, I then examine which aspects of children’s input best predict their mastery of modals. Preliminary results suggest that negation is predictive of children’s early success with necessity modals, and that frequency of modal talk, but not of particular lexemes, also contributes to their early success

Discovering Pronoun Categories using Discourse Information

Interpretation of a pronoun is driven by properties of syntactic distribution. Consequently, acquiring the meaning and the distribution are intertwined. In order to learn that a pronoun is reflexive, learners need to know which entity the pronoun refers to in a sentence, but in order to infer its referent they need to know that the pronoun is reflexive. This study examines whether discourse information is the information source that the learner might use to acquire grammatical categories of pronouns. Experimental results demonstrate that adults can use discourse information to accurately guess the referents of pronouns. Simulations show that a Bayesian model using guesses from the experiment as an estimate of the discourse information successfully categorizes English pronouns into categories corresponding to reflexives and non-reflexives. Together, these results suggest that knowing which entities are likely to be referred to in the discourse can help learners acquire grammatical categories of pronouns