bilingualism, ability to use two languages. Fluency in a second language requires skills in listening comprehension, speaking, reading, and writing, although in practice some of those skills are often considerably less developed than others. Few bilinguals are equally proficient in both languages. However, even when one language is dominant (see language acquisition), performance in the other language may be superior in certain situations—e.g., someone generally stronger in Russian than in English may find it easier to talk about baseball in English. Native speakers of two languages are sometimes called equilingual, or ambilingual, if their mastery of both languages is equal. Some bilinguals are persons who were reared by parents who each spoke a different language or who spoke a language different from the one used in school. In some countries, especially those with two or more official languages, schools encourage bilinguilism by requiring intensive study of a second language. Bilinguals sometimes exhibit code-switching, or switching from one language to the other in the middle of a conversation or even the same sentence; it may be triggered by the use of a word that is similar in both languages.
See G. Saunders, Bilingual Children (1988); K. Hyltenstam and L. K. Obler, ed., Bilingualism Across the Lifespan (1989).