2. Literature review

2.1 Definition of code-switching

 Code has been widely used in both linguistics and literature. In this paper, code refers to language used in EFL classroom. It is not difficult to determine what constitutes a code in English classroom discourse. 

Code-switching, like code, is a widespread phenomenon throughout the world which has generated much discussion and debate. Code-switching has been approached from different perspectives and defined by many scholars (Auer, 1998; Bentahila & Davies 1983; Eastman, 1992; Milroy & Muysken 1995; Poplack, 1980). Based on their different research goals and the kind of data they collected. Code-switching is defined from different approaches as structural, functional or psycholinguistic approaches. From the structural approaches. In general, a prerequisite for code-switching is a juxtaposition of elements from two codes (Winford, 2003). This study follows the definition of code-switching from the functional perspective. That is, code-witching in language classroom refers to any alternate use of two codes or languages either within one utterance or between one utterance and the next in an interactional discourse. 

Code-switching occurs when a speaker alternates between different languages in a conversation. It is a common and informal way of communication by multilingual speakers (Bullock & Toribio, 2009). As more people become multilingual, code-switching speech becomes more common.

2.2 Main approaches to analysis of code-switching 

2.2.1 Linguistic approach

To the linguistic approach, it has been observed that researchers have suggested different models derived from the current syntactic theories to explain the switching phenomena in bilingual or multilingual communities. There are also different patterns of switching in different communities which are mostly related to the typological characteristics of the language pairs involved in code-switching. Despite their disagreements over the properties of patterning, all the researchers agree on the question of the bilingual speakers' degree of competence. That is, code-switching is quite a normal and widespread form of bilingual interaction, requiring a great deal of bilingual competence. Linguistic models of code-switching with high levels of explanatory value are both an essential and a useful step in increasing self-awareness. However they may not necessarily be sufficient to explain why code-switching occurs in the bilingual/multilingual communities. A successful analysis of syntactic constraints alone cannot guarantee attitude change；therefore researchers should also consider the psychological factors in mixed language processing in bilingual speakers. 

2.2.2 Sociolinguistic approach

To the sociolinguistic approach, as bilinguals are linguistically competent in both languages, these researchers ask such questions as why the two distinct codes exist within a single utterance or a conversation；what specific discourse functions does code-switching serve in conversation and what factors influence a speaker's code choice. Auer (1998) employs conversation analysis(CA) to analyze performance data on CS. Auer argues that the meaning of code-switching needs to be interpreted in relation to the preceding and following utterances. For him, the sequential embeddedness of meaning in bilingual conversation is relatively independent of its social meaning for the community. Auer's pure structural analysis to code-switching neglects the social factors or norms on the bilingual behavior. 

Sociolinguistic approaches to code-switching emphasize both the functions that CS serves in the communities and the factors that influence code choice. However, it is argued that sociolinguistic study of code-switching cannot proceed without a solid theoretical structural analysis. All the above researches focus on language alternation in the natural bilingual/multilingual communities. Even those who study code-switching in language classroom neglect one or another aspect of code-switching. However, those researches on code-switching may help us understand classroom interaction and how differences in interaction norms in EFL classroom influence not only the learning environment but also the level of student achievement.