Language input and outcome variation as a test of theory plausibility: The case of early phonological acquisition

There is wide individual, social, and cultural variation in experiences afforded to young children, yet current evidence suggests there is little variation in phonological outcomes in the first year of life. This paper provides a classification of phonological acquisition theories, revealing that few of them predict no variation in phonological acquisition outcomes, and thus are plausible in view of observed patterns: Only theories with strong priors and informational filters, and where phonological acquisition does not depend on lexical development, are compatible with great variation in early language experiences resulting in minimal or no outcome variation. The approach is then extended to consider proposals contemplating acquisition of other linguistic levels, including joint learning frameworks, and testable predictions are drawn for the acquisition of morphosyntax and vocabulary.