This dissertation examines the acquisition of argument structure as a window into the role of development in grammar learning. The way that children represent the data for language acquisition depends on the grammatical knowledge they have at any given point in development. Children use their immature grammatical knowledge, together with other non-linguistic conceptual, pragmatic, and cognitive abilities, to parse and interpret their input. But until children have fully acquired the target grammar, these input representations will be incomplete and potentially inaccurate. Our learning theory must take into account how learning can operate over input representations that change over the course of development. What allows learners to acquire new knowledge from partial and noisy representations of their data, one step at a time, and still converge on the right grammar?

The case study in this dissertation points towards one way to characterize the role of development in grammar acquisition by probing more deeply into the resources that learners bring to their learning task. I consider two types of resources. The first is representational: learners need resources for representing their input in useful ways, even early in development. In two behavioral studies, I ask what resources infants in their second year of life use to represent their input for argument structure acquisition. I show that English learners differentiate the grammatical and thematic relations of clause arguments, and that they recognize local argument relations before they recognize non-local predicate-argument dependencies. The second type of resource includes mechanisms for learning from input representations even when they are incomplete or inaccurate early in development. In two computational experiments, I investigate how learners could in principle use a combination of domain-specific linguistic knowledge and domain-general cognitive abilities in order to draw accurate inferences about verb argument structure from messy data, and to identify the forms that argument movement can take in their language.

By investigating some of the earliest steps of syntax acquisition in infancy, this work aims to provide a fuller picture of what portion of the input is useful to an individual child at any single point in development, how the child perceives that portion of the input given her current grammatical knowledge, and what internal mechanisms enable the child to generalize beyond her input in inferring the grammar of her language. This work has implications not only for theories of language learning, but also for learning in general, by offering a new perspective on the use of data in the acquisition of knowledge.