This thesis is composed of five parts. Part one is an introduction. In this part it gives a brief introduction to the theory background, the purpose and the organization of this thesis. Part two is the literature review, in which the definitions of interlanguage and interlanguage variation are introduced and some related studies are also reviewed. The factors that cause interlanguage variation are presented in part three, including linguistic factors and non-linguistic factors. In part four, the writer summarizes some implications for English Language Teaching in China. Part five is the conclusion of this thesis. What’s more, some suggestions for further study are also presented.源'自:751]'论-文'网"]www.751com.cn

2. Literature Review

2.1 Definition of Interlanguage

Interlanguage is defined “as the linguistic system evidences when adult second language learners attempted to express meanings in the language being learned” (Diane and Michael, 2000: 71). However, Ellis points out that “various alternative terms have been implemented by different researchers to refer to the same phenomenon” (Ellis, 1999: 47). Nemser (1971) refers to approximate systems, and Corder (1971) to idiosyncratic dialects and transitional competence. These terms reflected two related but different concepts. First, interlanguage refers to the structured system which the learner constructs at any given stage in his development. Second, the term refers to the series of interlocking systems, which form what Corder (1967) called the learner’s built-in syllabus. In summary, the concept of interlanguage “is established as learners’ independent system of the second language, which is of neither the native language nor the second language, but a continuum or approximation from one extreme of his native language to the other the second language” (Dai Weidong & He Zhaoxiong, 2010: 160). According to Yang Lianrui (2012), interlanguage is independent, systematic, dynamic, and permeable. Interlanguage is also a process that reflects learning psychology.

2.2 Definition of Interlanguage Variation

According to Tarone, interlanguage variation “is the tendency for a second language learner’s utterances, produced in the attempt to convey meaning, to vary systematically in grammatical and phonological accuracy as specific situational features change” (Tarone, 1998: 73). This variation in grammatical accuracy can occur within one time frame; sometimes within minutes, which can be called synchronic. And sometimes the variation is quite predictable in response to specific changes in features of situational context and task. A shift in grammar accuracy might occur when the topic changes. In general, the interlanguage variation can occur at any linguistic level including syntactic, phonological, morphological or lexical level.