Abstract
The process of the acquisition of morphemes attached to Japanese verbs has not been established by researchers, and there has been no systematic investigation of the acquisition order of verb morphemes. Study 1 analyzed longitudinal speech data of 4 mother-child dyads between 1–3 years of age, and revealed that a common sequence existed in children's acquisition of verb morphemes. Possible contributing factors were semantic complexity, complexity of morphological structure, and maternal input. Study 2 examined morpheme input frequency and variations of stem-morpheme combinations in mothers' speech, based on the data from 3 mother-child dyads. The results showed that the acquisition order of a child correlated with the input frequency and variation indices of his mother; these indices also correlated even among the mothers. These findings suggest that maternal speech tends to share the same pragmatic functions and perspectives in conversations as those of children. Children may also have similar tendencies in their verbal expressions.
