- to report what someone has said, a girl who is telling a story switches from Tok Pisin (a language of Papua New Guinea) to English to report what the man said: "Lapun man ia cam na tok, 'oh yu poor pussiket'" (The old man came and said 'you poor pussycat').

- some topics are more appropriate to one language than another. Mexican Americans for example prefer to talk about money in English rather than in Spanish - "La consulta èra eight dollars". (the visit cost $8)

- the choice of language shows the speaker's role. A Kenyan man who was serving his own sister in a shop started in their own Luiyia dialect and then switched to Swahili for the rest of the conversation to signal that he was treating her as an ordinary customer.

84% of switches within the sentence are isolated words, say the English/Malaysian "Ana free hari ini" (Ana is free today) where English is switched to only for the item "free"

10% are phrases as in the Russian/French "Imela une femme de chambre" (She had a chambermaid)

6% are switches for whole clauses as in the German/English "Papa, wenn du das Licht ausmachst, then I'll be so lonely" (Daddy, if you put out the light, I'll be so lonely).

Poplack (1980) claims that there are two main restrictions on where switching can happen:

i) the 'free morpheme constraint'. The speaker must not switch language between a word and its endings unless the word is pronounced as if it were in the language of the ending. Thus an English/Spanish switch "runeando" is impossible because "run" is distinctively English in sound. But "flipeando" is possible because "flip" could be a Spanish word.

ii) the 'equivalence constraint'. The switch must come at a point in the sentence where it does not violate the grammar of either language. So there should be no French/English switches such as "a car americaine" or "une American voiture" as they would be wrong in both languages. It is possible however to have the French/English switch "J'ai acheté an American car" (I have bought an American car) because both English and French share the construction in which the object follows the verb.

Gardner-Chloros, P. (1992) The sociolinguistics of the Greek-Cypriot community of London. In M. Karyolemou ed., Sociolinguistique du grec et de Ia Grèce, 4 (June 1992). Plurilinguismes. CERPL Paris: Université René Descartes, 112-36.

Grosjean, F. (1989), 'Neurolinguists, beware! The bilingual is not two monolinguals in one person', Brain and Language, 36, 3-15

Grosjean, F., & Soares, C. (1986) 'Processing mixed language, some preliminary findings', in Vaid, J. (ed.) (1986), Language Processing in Bilinguals: Psycholinguistic and Neurolinguistic Perspectives, LEA

Kolers, P.A. (1966), 'Interlingual facilitation of short-term memory', JVLVB, 5, 314-319

Macnamara, J. & Kushnir, S. (1971), 'Language switching in bilinguals as function of stimulus and response uncertainty', J. Exp. Psych., 78, 208-215

Milroy, L. & Muyskens, P. (eds.) (1995). One Speaker, Two Languages. CUP

Myers-Scotton, C. (1993) Duelling languages: grammatical structure in code-switching. Oxford: Clarendon Press.

Myers-Scotton, C.(1993), Social motivations for codeswitching: evidence from Africa. Clarendon

Poplack, S. (1980), 'Sometimes I'll start a sentence in English y termino en espanol', Linguistics, 18, 581-616

Romaine, S. (1989), Bilingualism, Blackwell, Oxford

Sridhar S.N., & Sridhar K.K. (1980) 'The syntax and psycholinguistics of bilingual code mixing', Can. J. Psychol., 34/4, 407- 416

Woolford, E. (1983), 'Bilingual code-switching and linguistic theory', 14, 3, Linguistic Inquiry, 520-536

.... Such ease of code-switching would be impossible if the languages were not intimately related rather than two compartmentalised systems. To quote Woolford (1983), 'The two monolingual grammars cooperate in the production of codeswitched utterances, but none of the rules are altered in any way'. ..........There are therefore systematic access points between the two language systems in multi-competence; the two systems form one supersystem. As Sridhar & Sridhar (1980) put it, 'Not only are elements from two languages present in the same sentence, these elements are integrated into a unified syntactic structure by a complex interaction of constraints'. The very naturalness, smoothness and comprehensibility of codeswitching is evidence in favour of wholistic multi-competence. In the words of Sridhar & Sridhar (1980, p.413), 'The right approach, therefore, seems to be to avoid both the strong linguistic independence model and the merged system model in favour of an interactionist model of overlapping systems'.

One objection to this is that switching from one language to another takes time. In early research Kolers (1966) found that code-switching added about 0.3 to 0.5 seconds per switch to reading aloud, while Macnamara & Kushnir (1971) found 0.2 seconds per switch in silent reading. Sridhar and Sridhar (1980) argue that much of this increased time is an artefact of the experiments; the texts were not usually codeswitched according to the proper constraints but jumbles of two languages. Nevertheless it does not count against multi-competence if operating the constraints of the mixed language mode adds some minimal processing time to speaking. ....

3. English/French: Philip, who is staying in France, is phoning his English nanny:
Philip: Maman, quel numéro il faut faire? ('Mum, what number should I dial?')
Mother: C'est écrit sur la carte qui est devant toi. (It's written on the card in front of you.)’ (Philip dials the number)
Philip: Hello, Nanny, how are you?