2. The bilingual's linguistic behavior One of the most interesting aspects of bilingualism is the fact that two (or more) languages are in contact within the same person. This phenomenon, which has led to a vast body of research, can best be understood if one examines the bilingual's various language modes. In their everyday lives, bilinguals find themselves at various points along a situational continuum which induce different language modes. At one end of the continuum, bilinguals are in a totally monolingual mode in that they are speaking (or writing) to monolinguals of one - or the other - of the languages that they know. At the other end of the continuum, bilinguals find themselves in a bilingual language mode in that they are communicating with bilinguals who share their two languages and with whom they normally mix languages (i.e. code-switch and borrow; see below). For convenience, we will refer to the two end points of the continuum when speaking of the monolingual or bilingual language modes, but we should keep in mind that these are end points and that intermediary modes do exist. This is the case, for example, when a bilingual is speaking to another bilingual who never mixes languages, or when a bilingual is interacting with a person who has limited knowledge of the other language. We should note also that bilinguals differ among themselves as to the extent they travel along the continuum; some rarely find themselves at the bilingual end whereas others rarely leave this end (for example, bilinguals who live in tight knit bilingual communities where the language norm is mixed language).
2.1 The monolingual language mode
In this mode, bilinguals adopt the language of the monolingual interlocutor(s) and deactivate their other language(s) as completely as possible. Bilinguals who manage to do this totally and, in addition, who speak the other language fluently and have no foreign accent in it, will often "pass" as monolinguals. Although such cases are relatively rare, it is precisely these that have led people to think that bilinguals are (or should be) two monolinguals in one person. In fact, deactivation of the other language is rarely total as is clearly seen in the interferences bilinguals produce (these are also known as between-language deviations). An interference is a speaker-specific deviation from the language being spoken due to the influence of the other "deactivated" language. Interferences can occur at all levels of language (phonological, lexical, syntactic, semantic, pragmatic) and in all modalities (spoken, written or sign). They are of two kinds: static interferences which reflect permanent traces of one language on the other (such as a permanent accent, the meaning extensions of particular words, specific syntactic structures, etc.) and dynamic interferences which are the ephemeral intrusions of the other language (as in the case of the accidental slip on the stress pattern of a word due to the stress rules of the other language, the momentary use of a syntactic structure taken from the language not being spoken, etc.). Examples of interferences produced by a French person speaking English are as follows. At the phonetic level, pronouncing Sank evven for dees instead of Thank heaven for this; at the lexical level, using corns (from French cornes) instead of horns in Look at the corns on that animal! ; at the syntactic level, saying I saw this on the page five (instead of on page five), and in writing, misspelling adress or appartment (based on the French adresse and appartement).
In addition, if one of the bilingual's languages is mastered only to a certain level of proficiency, deviations due to the person's interlanguage (also known as within-language deviations) will also occur. These include overgeneralizations (for example, taking irregular verbs and treating them as if they were regular), simplifications (dropping pluralization and tense markers, omitting functions words, simplifying the syntax, etc.) as well as hypercorrections and the avoidance of certain words and expressions. Between- and within-language deviations are clearly observable when bilinguals are in a monolingual language mode but they also occur in the bilingual language mode (see below). It should be noted finally that both types of deviations, although sometimes quite apparent (such as a foreign accent), usually do not interfere with communication. This is because bilinguals develop their languages to the level of fluency required by the environment. Deviations in bilingual speech are thus of the same nature as slips of the tongue and hesitation phenomena. They are present but do not usually affect communication.
2.2 The bilingual language mode.
In this mode, bilinguals interact with one another. First they adopt a language to use together, what is known as the "base language" (also the "host" or "matrix" language). This process is called "language choice" and is governed by a number of factors: the interlocutors involved (i.e. their usual language of interaction, their language proficiency, language preference, socioeconomic status, age, sex, occupation, education, kinship relation, attitude toward the languages, etc;); the situation of the interaction (location, presence of monolinguals, degree of formality and of intimacy), the content of the discourse (topic, type of vocabulary needed) and the function of the interaction (to communicate information, to create a social distance between the speakers, to raise the status of one of the interlocutors, to exclude someone, to request something, etc.). Language choice is a well-learned behavior (a bilingual rarely asks the conscious question, "Which language should I be using with this person?") but it is also a very complex phenomenon which only becomes apparent when it breaks down. Usually, bilinguals go through their daily interactions with other bilinguals quite unaware of the many psychological and sociolinguistic factors that interact to help choose one language over another. We should note that the base language can change several times during a single conversation if the situation, topic, interlocutor, etc. require it.
Once a base language has been chosen, bilinguals can bring in the other language (the "guest" or "embedded" language) in various ways. One of these ways is to code-switch, that is to shift completely to the other language for a word, a phrase, a sentence. (For example, Va chercher Marc and bribe him avec un chocolat chaud with cream on top (Go get Marc and bribe him with a hot chocolate with cream on top)). Code-switching has long been stigmatized, and has been given a number of pejorative names such as Franglais (the switching between French and English) or Tex-Mex (the switching between English and Spanish in the southwestern part of the United States). The consequence of this has been that some bilinguals never switch while others restrict it to situations in which they will not be stigmatized for doing so. Recently, code-switching has received considerable attention from researchers. For example, sociolinguists have concentrated on when and why switching takes place in the social context. Reasons that have been put forward are: to fill a linguistic need, to continue the last language used, to quote someone, to specify the addressee, to exclude someone from the conversation, to qualify a message, to specify speaker involvement, to mark group identity, to convey emotion, to change the role of the speaker, etc. Linguists, on the other hand, have sought to study the types of code-switches that occur (single words, phrases, clauses, sentences, etc.) as well as the linguistic constraints that govern their appearance. Although there is still considerable controversy over this latter aspect (are constraints universal or language specific? how broad can a constraint be?) is it now clear that switching is not simply a haphazard behavior due to some form of "semilingualism" but that it is, instead, a well governed process used as a communicative strategy to convey linguistic and social information.
The other way bilinguals can bring in the other, less activated, language is to borrow a word or short expression from that language and to adapt it morphologically (and often phonologically) into the base language. Thus, unlike code-switching which is the juxtaposition of two languages, borrowing is the integration of one language into another. Most often both the form and the content of a word are borrowed (to produce what has been called a loanword or more simply a borrowing) as in the following examples taken from French-English bilinguals: "Ca m'étonnerait qu'on ait code-switché autant que ça" (I can't believe we code-switched as often as that) and "Maman, tu peux me tier /taie/ mes chaussures" (Mummy, can you tie my shoes?). In these examples, the English words "code-switch" and "tie" have been brought in and integrated into the French sentence. A second type of borrowing, called a loanshift, consists in either taking a word in the base language and extending its meaning to correspond to that of a word in the other language, or rearranging words in the base language along a pattern provided by the other language and thus creating a new meaning. An example of the first kind of loanshift would be the use of humoroso by Portuguese-Americans to mean 'humorous' when the original meaning is 'capricious'. An example of the second kind is the use of idiomatic expressions that are translated literally from the other language, such as "I put myself to think about it" said by a Spanish-English bilingual, based on "Me puse a pensarlo". It is important to distinguish idiosyncratic loans (also called "speech borrowings" or "nonce borrowings") from words which have become part of a language community's vocabulary and which monolinguals also use (called "language borrowings" or "established loans"). Thus, in the following text, every third or fourth word is an established loan from French which has now become part of the English language: "The poet lived in the duke's manor. That day, he painted, played music and wrote poems with his companions." Current research is examining, among other things, the differences and similarities that exist between code-switches and borrowings (and within the latter, between idiosyncratic borrowings and established borrowings), as well as the impact of the two on language itself, such as first- and second-language restructuring.