Rethinking structural growth: Insights from the acquisition of interactional language

In this paper, we introduce a novel proposal for the acquisition of syntactic structure. Most studies of syntactic first language acquisition focus on the increasingly complex expression of propositional thought. Layer by layer, from the bottom up, child language matures into adult-like representations. We challenge this account of an upward growing syntax based on evidence from early interactional language, which has largely been ignored in the study of syntactic acquisition. Given that interactional units of language are associated with the topmost layers of syntactic structure, and given that they are acquired early, it follows that syntactic acquisition cannot be characterized by upward growth. Rather, we propose that syntactic acquisition proceeds in an inward fashion. We present a case study of the early uses of utterance-final huh (an interactional unit of language) in North American child English that supports this hypothesis. We thus introduce the Inward Growing Spine Hypothesis as a research agenda.