Late generalization of morphological causatives: Evidence from Turkish
Children’s spontaneous speech may not reflect true productivity with grammar rules. We investigated Turkish-learning children’s rule-based understanding of causative morphology by combining experimental and corpus work. We asked (1) when the generalization of causative morphology emerges and (2) what role input plays in this development. To answer the first question, Study 1 experimentally tested 106 children aged 2;6–6;1 on a language judgment task using pseudo-verbs. Children preferred the causative marker -DIr over an incongruent suffix for causativized events earliest at age 4;10. Further, Study 2 tested 38 children aged 3;6–4;6 and revealed no preference of -DIr over no suffix. Study 3 examined a corpus for child-directed input and showed that the variation of verb stems to which -DIr was attached remained lower than variation of verbs eligible to take -DIr, up to age 3. The findings suggest that rule-based understanding of morphological causatives emerges much later than previously proposed productivity at age 2, which might be accounted for by the insufficient variation of morphological causatives in the early input.