The Development of Causal Structure without a Language Model.

Across a diverse range of languages, children proceed through similar stages in their production of causal language: their initial verbs lack internal causal structure, followed by a period during which they produce causative overgeneralizations, indicating knowledge of a productive causative rule. We asked in this study whether a child not exposed to structured linguistic input could create linguistic devices for encoding causation and, if so, whether the emergence of this causal language would follow a trajectory similar to the one observed for children learning language from linguistic input. We show that the child in our study did develop causation-encoding morphology, but only after initially using verbs that lacked internal causal structure. These results suggest that the ability to encode causation linguistically can emerge in the absence of a language model, and that exposure to linguistic input is not the only factor guiding children from one stage to the next in their production of causal language.