1. Describing the bilingual Although a few researchers have defined bilinguals as those who have native-like control of two or more languages, most others agree that this position is not realistic. If one were to count as bilingual only those people who pass as monolinguals in each of their languages, one would be left with no label for the vast majority of people who use two or more languages regularly but who do not have native-like fluency in each. This has led researchers to propose other definitions of bilingualism, such as: the ability to produce meaningful utterances in two (or more) languages, the command of at least one language skill (reading, writing, speaking, listening) in another language, the alternate use of several languages, etc. For our purposes, we will call bilingual those people who use two (or more) languages (or dialects) in their everyday lives. (Throughout this entry, we will subsume dialects under the term "language"). Thus, our definition includes people ranging from the migrant worker who speaks with some difficulty the host country's language (and who cannot read and write it) all the way to the professional interpreter who is totally fluent in two languages. In between we find the foreign spouse who interacts with friends in his first language, the scientist who reads and writes articles in a second language (but who rarely speaks it), the member of a linguistic minority who uses the minority language at home only and the majority language in all other domains of life, the deaf person who uses sign language with her friends but a signed form of the spoken language with a hearing person, etc. Despite the great diversity that exists between these people, all share a common feature: they lead their lives with two (or more) languages. (Bilinguals who are no longer using their different languages but who have retained knowledge of them will be termed "dormant bilinguals").
The reasons that bring languages into contact and hence foster bilingualism are many: migrations of various kinds (economic, educational, political, religious), nationalism and federalism, education and culture, trade and commerce, intermarriage, etc. These factors create various linguistic needs in people who are in contact with two or more languages and who develop competencies in their languages to the extent required by these needs. In contact situations it is rare that all facets of life require the same language (people would not be bilingual if that were so) or that they always demand two languages (language A and B at work, at home, with friends, etc.). In fact, bilinguals acquire and use their languages for different purposes, in different domains of life, with different people. It is precisely because the needs and uses of the languages are usually quite different that bilinguals rarely develop equal fluency in their languages. The level of fluency attained in a language (more precisely, in a language skill) will depend on the need for that language and will be domain specific. It is thus perfectly normal to find bilinguals who can only read and write one of their languages, who have reduced speaking fluency in a language they only use with a limited number of people, or who can only speak about a particular subject in one of their languages. This explains in part why bilinguals are usually poor interpreters and translators. Not only are specific skills required, but interpretation and translation entail that one has identical lexical knowledge in the two languages, something that most bilinguals do not have. Certain domains and topics are covered by the lexicon of one language, others by the lexicon of the other language, and some few by the two. Interpreting and translating when one lacks the appropriate vocabulary and the necessary skills is thus something that bilinguals find difficult.
The failure to understand that bilinguals normally use their languages for different purposes, with different people and in different domains of life has been a major obstacle to obtaining a clear picture of bilinguals and has had many negative consequences: bilinguals have been described and evaluated in terms of the fluency and balance they have in their two languages; language skills in bilinguals have almost always been appraised in terms of monolingual standards; research on bilingualism has in large part been conducted in terms of the bilingual's individual and separate languages; and, finally, many bilinguals evaluate their language competencies as inadequate. Some criticize their mastery of language skills, others strive their hardest to reach monolingual norms, others hide their knowledge of their "weaker" language, and most simply do not perceive themselves as being bilingual even though they use two (or more) languages in their everyday lives.
Researchers are now starting to view the bilingual not so much as the sum of two (or more) complete or incomplete monolinguals but rather as a specific and fully competent speaker-hearer who has developed a communicative competence that is equal, but different in nature, to that of the monolingual. This competence makes use of one language, of the other, or of the two together (in the form of mixed speech; see below) depending on the situation, the topic, the interlocutor, etc. This in turn has led to a re-definition of the procedure used to evaluate the bilingual's competencies. Bilinguals are now being studied in terms of their total language repertoire, and the domains of use and the functions of the bilingual's various languages are being taken into account.
We should note finally that as the environment changes and the needs for particular language skills also change, so will the bilingual's competence in his or her various language skills. New situations, new interlocutors, new language functions will involve new linguistic needs and will therefore change the language configuration of the person involved. Extreme cases of restructuring are language forgetting and a return to functional monolingualism, be it in the person's first, second or third language.