Grammatical complexity: ‘What Does It Mean’ and ‘So What’ for L2 writing classrooms?

Grammatical complexity is regarded as a crucial feature of L2 writing. The construct has been widely utilized in empirical research to gauge L2 writing quality and development, particularly in English. Nevertheless, a question of paramount importance, i.e., what constitutes complexity, has not yet received adequate attention. Drawing on Bulté and Housen's (2012) taxonomy of L2 complexity, we conducted a comprehensive and in-depth review of changes in the definition of grammatical complexity over the past two decades. Our finding suggests that grammatical complexity has been theorized from two primary perspectives: an independent perspective that grammatical complexity is static across different contexts and a dependent perspective that grammatical complexity should be investigated in response to specific registers. Also, grammatical complexity has been observed from primarily the clausal level to the clausal, phrasal and morphological levels, echoing Norris and Ortega's (2009) claim that grammatical complexity should be studied as a multi-dimensional construct. Moreover, we have identified four main parameters used by existing literatures to define grammatical complexity: length, ratio, index and frequency. The change of each parameter is summarized with details in our review. At the end, we also discuss pedagogical implications for L2 writing instruction in the EAP context.