|Areas of study|
Some scholars use the terms "code-mixing" and "code-switching" interchangeably, especially in studies of syntax, morphology, and other formal aspects of language. Others assume more specific definitions of code-mixing, but these specific definitions may be different in different subfields of linguistics, education theory, communications etc.
Code-mixing is similar to the use or creation of pidgins; but while a pidgin is created across groups that do not share a common language, code-mixing may occur within a multilingual setting where speakers share more than one language.
Code-mixing as code-switching
Some linguists use the terms code-mixing and code-switching more or less interchangeably. Especially in formal studies of syntax, morphology, etc., both terms are used to refer to utterances that draw from elements of two or more grammatical systems. These studies are often interested in the alignment of elements from distinct systems, or on constraints that limit switching.
While many linguists have worked to describe the difference between code-switching and borrowing of words or phrases, the term code-mixing may be used to encompass both types of language behavior.
While the term code-switching emphasizes a multilingual speaker's movement from one grammatical system to another, the term code-mixing suggests a hybrid form, drawing from distinct grammars. In other words, code-mixing emphasizes the formal aspects of language structures or linguistic competence, while code-switching emphasizes linguistic performance.
Code-mixing in sociolinguistics
While linguists who are primarily interested in the structure or form of code-mixing may have relatively little interest to separate code-mixing from code-switching, some sociolinguists have gone to great lengths to differentiate the two phenomena. For these scholars, code-switching is associated with particular pragmatic effects, discourse functions, or associations with group identity. In this tradition, the terms code-mixing or language alternation are used to describe more stable situations in which multiple languages are used without such pragmatic effects. See also Code-mixing as fused lect, below.
Code-mixing in language acquisition
In studies of bilingual language acquisition, code-mixing refers to a developmental stage during which children mix elements of more than one language. Nearly all bilingual children go through a period in which they move from one language to another without apparent discrimination. This differs from code-switching, which is understood as the socially and grammatically appropriate use of multiple varieties.
Beginning at the babbling stage, young children in bilingual or multilingual environments produce utterances that combine elements of both (or all) of their developing languages. Some linguists suggest that this code-mixing reflects a lack of control or ability to differentiate the languages. Others argue that it is a product of limited vocabulary; very young children may know a word in one language but not in another. More recent studies argue that this early code-mixing is a demonstration of a developing ability to code-switch in socially appropriate ways.
For young bilingual children, code-mixing may be dependent on the linguistic context, cognitive task demands, and interlocutor. Code-mixing may also function to fill gaps in their lexical knowledge, and such lexical uncertainty may subsequently lead to naming errors. 
Code-mixing in psychology and psycholinguistics
In psychology and in psycholinguistics the label code-mixing is used in theories that draw on studies of language alternation or code-switching to describe the cognitive structures underlying bilingualism. During the 1950s and 1960s, psychologists and linguists treated bilingual speakers as, in Grosjean's term, "two monolinguals in one person." This "fractional view" supposed that a bilingual speaker carried two separate mental grammars that were more or less identical to the mental grammars of monolinguals and that were ideally kept separate and used separately. Studies since the 1970s, however, have shown that bilinguals regularly combine elements from "separate" languages. These findings have led to studies of code-mixing in psychology and psycholinguistics.
Sridhar and Sridhar define code-mixing as "the transition from using linguistic units (words, phrases, clauses, etc.) of one language to using those of another within a single sentence." They note that this is distinct from code-switching in that it occurs in a single sentence (sometimes known as intrasentential switching) and in that it does not fulfill the pragmatic or discourse-oriented functions described by sociolinguists. (See Code-mixing in sociolinguistics, above.) The practice of code-mixing, which draws from competence in two languages at the same time suggests that these competences are not stored or processed separately. Code-mixing among bilinguals is therefore studied in order to explore the mental structures underlying language abilities.
Code-mixing as fused lect
A mixed language or a fused lect is a relatively stable mixture of two or more languages. What some linguists have described as "codeswitching as unmarked choice" or "frequent codeswitching" has more recently been described as "language mixing", or in the case of the most strictly grammaticalized forms as "fused lects".
In areas where code-switching among two or more languages is very common, it may become normal for words from both languages to be used together in everyday speech. Unlike code-switching, where a switch tends to occur at semantically or sociolinguistically meaningful junctures, this code-mixing has no specific meaning in the local context. A fused lect is identical to a mixed language in terms of semantics and pragmatics, but fused lects allow less variation since they are fully grammaticalized. In other words, there are grammatical structures of the fused lect that determine which source-language elements may occur.
A mixed language is different from a creole language. Creoles are thought to develop from pidgins as they become nativized. Mixed languages develop from situations of code-switching. (See the distinction between code-mixing and pidgin above.)
- Although this article uses the terms speech and speaking following common practice in linguistics, these descriptions apply equally to signed languages.
- Muysken, Pieter. 2000. Bilingual Speech: A Typology of Code-mixing. Cambridge University Press. ISBN 0-521-77168-4
- Bokamba, Eyamba G. 1989. Are there syntactic constraints on code-mixing? World Englishes, 8(3), 277-292.
- See especially Social motivations for code-switching.
- King, Kendall A. 2006. "Child language acquisition." In R. Fasold and J. Connor-Linton (eds.) An Introduction to Language and Linguistics. Cambridge University Press. pp. 205-224.
- Greene, Kai J; Elizabeth D Peña and Lisa M Bedore (2012). "Lexical choice and language selection in bilingual preschoolers". Child Language Teaching and Therapy 29 (1): 27–39. doi:10.1177/0265659012459743.
- Grosjean, Francois. 1989. Neurolinguists, beware! The bilingual is not two monolinguals in one person. Brain language 36(1):3-15.
- Sridhar, S.N. and Kamal K. Sridhar. 1980. The syntax and psycholinguistics of bilingual code-mixing. Canadian Journal of Psychology 34(4):407-416.
- Myers-Scotton, Carol. 1993. Social Motivations of Codeswitching. Oxford: Clarendon Press.
- Poplack, Shana. 1979. Sometimes I'll start a sentence in Spanish y termino en espanol: toward a typology of code-switching. Linguistics 18(233-234): 581-618.
- Auer, Peter. 1999. From code-switching via language mixing to fused lects: toward a dynamic typology of bilingual speech. International Journal of Bilingualism 3(4):309-332.
- See also Contextualization (sociolinguistics).
- Wardhaugh, Ronald. 2002. "Pidgins and Creoles." In An Introduction to Sociolinguistics (fourth ed.). Blackwell. pp. 57–86
- Romaine, Suzanne and Braj Kachru. 1992. "Code-mixing and code-switching." In T. McArthur (ed.) The Oxford Companion to the English Language. Oxford University Press. pp. 228-229.