Abstract
This study examined developmental changes in the internal state language of a young child, in relation to understanding of his younger brother's intentions. A 21 month-old boy and his newborn brother were videotaped at home in unstructured observations over a period of 17 months. There were 2 types of analyses. We first examined the boy's utterances about his self and about his brother's internal state language. Second, to consider developmental changes in comprehension of his brother's intetions, references to intentions and the context of intentions were analyzed. The results showed important age-related changes concerning mental states. Mental terms (e.g., verbs such as "know") appeared at 32 months about both self and the baby brother, and increased by 37 months. The acquisition of such terms enabled the boy to accurately grasp and report his brother's intentions. These observations suggest that emergence of mental verbs about self and others is highly correlated with understanding of intentions.
