Sequence and system in the acquisition of tense and agreement

Purpose: The relatedness of tense morphemes in the language of children younger than 3 years of age is a matter of controversy. Generativist accounts predict that the morphemes will be related, whereas usage-based accounts predict the absence of relationships. This study focused on the increasing productivity of the 5 morphemes in the tense productivity score (copula BE, third-person singular present -3s, past -ed, auxiliary DO, auxiliary BE; Hadley & Short, 2005) and their relationship to one another. Method: Twenty typically developing children were observed longitudinally from 21 to 33 months of age. One hour of naturalistic caregiver-child interaction sampled every 3 months was analyzed. Results: Copula BE was more productive than all other morphemes from age 27 months onward. Auxiliary BE was significantly less productive than -3s, -ed, and DO from age 27 months onward. Evaluation of third-person singular tense morphemes at age 33 months revealed that the productivity scores of copula is, -3s, and does were all correlated. Conclusions: There is sequence and simultaneity in development that no prior framework has fully explained, as well as evidence of cross-morpheme relationships. In this article, the authors interpret these findings as support for the gradual morphosyntactic learning hypothesis (Rispoli & Hadley, 2011; Rispoli, Hadley, & Holt, 2009).