Language acquisition is like climbing a staircase, with each step representing a new milestone. In the case of Turkish causatives, we explored how children progress from using familiar verbs to understanding and producing novel ones. Previous studies have shown that children as young as 2 to 3 years old can use causal markers with verbs they are familiar with. However, little was known about their comprehension and application of causative morphology with new verbs. Through comprehension-judgment experiments, we discovered that children start generalizing the causative suffix -DIr in a novel context around the age of 4;10. Additionally, our analysis of caregiver speech revealed that they consistently used the -DIr suffix when addressing younger children. These findings suggest that productivity with morphological causatives takes time to develop and may be influenced by the linguistic input provided by caregivers. To delve deeper into this fascinating area of research on language acquisition, explore the full article!

Abstract
Becoming productive with grammatical categories is a gradual process in children’s language development. Here, we investigated this transition process by focusing on Turkish causatives. Previous research examining spontaneous and elicited production of Turkish causatives with familiar verbs attested the onset and early stages of productivity at ages 2 to 3 (Aksu-Koç & Slobin, 1985; Nakipoğlu, Uzundag, & Sarıgül, 2021). So far, however, we know very little about children’s understanding of causatives with novel verbs. In the present study, we asked: (a) When does the generalization of causative morphology in a novel context emerge? and (b) What role does child-directed input play in this development? To answer the first question, we conducted comprehension-judgment experiments with children aged 2;6–6;11 using pseudo-verbs (Study 1 & 2). Results showed that children preferred the Turkish causative suffix -DIr over an unrelated or no suffix to denote caused events earliest at age 4;10. To answer the second question, we analyzed child-directed speech from a longitudinal corpus of Turkish language acquisition (Study 3). Results showed that when addressing children younger than age 3, caregivers used the -DIr suffix with little variation considering the overall variability of verbs they could utter. Overall, these findings suggest that productivity with morphological causatives in a novel context emerges in a later stage of acquisition. This later development might partly be accounted for by the insufficient variation of morphological causatives in the early input.

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