In acquiring communicative competence, children must learn to speak not only grammatically but also appropriately. Although rules for appropriate language use may vary from culture to culture, they are usually sensitive across languages to many of the same factors, including the context and the topic of the discourse, and the sex, age, familiarity and relative status of the speaker and the listener. There is available detailed evidence of the ways in which adults consistently modify their speech to foreigners, of phonological, syntactic, and lexical markings of language in professional...