This chapter is concerned with the study of children who acquire two languages simultaneously. In such cases, it is inappropriate to speak of first and second languages. Both languages are first languages, although one usually dominates in certain situations or with certain persons. If children hear one language from their parents and another from their playmates, for example, they will tend to speak the parents' language when in contact with them and will restrict the other language to the play situation. If contact with parents is much more extensive than contact with playmates, the language the child speaks with parents is likely to predominate. Perfect linguistic balance across situations seems difficult, f not impossible, to achieve, since amount of exposure across situations is never constant.
Bilingualism admits of degrees, however. This is consistent with the definition adopted in the first chapter: the ability to produce complete and meaningful utterances in two languages. Although bilingual children may be more fluent in one language in certain spheres than in the other language, they can produce complete and meaningful utterances in both. For the most part, the children studied in the research considered in this chapter were able to communicate with ease at a level appropriate for their age in either language. In some cases there were shifts in dominance from time to time as the child moved from a bilingual to a monolingual environment, but usually the child adjusted to the bilingual environment when placed in it again.
One problem in speaking of the simultaneous acquisition of two languages is defining a cutoff point at which one language can be said to have been established. If a 2½-year-old, English-speaking child moves to France and starts to acquire French, is the child simultaneously acquiring