Abstract 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 Bulte 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.

中文翻译：

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语法复杂性：L2 写作课堂的“这是什么意思”和“那又如何”？

摘要 语法复杂性被认为是二语写作的一个重要特征。该结构已被广泛用于实证研究，以衡量 L2 写作质量和发展，尤其是在英语中。然而，一个最重要的问题，即复杂性的构成，尚未得到足够的重视。借鉴 Bulte 和 Housen (2012) 的 L2 复杂性分类法，我们对过去二十年中语法复杂性定义的变化进行了全面深入的审查。我们的发现表明，语法复杂性已从两个主要角度进行理论化：独立的观点认为语法复杂性在不同的上下文中是静态的，以及应根据特定的语域研究语法复杂性的依赖观点。还，语法复杂性主要是从小句级别到小句、短语和形态级别，这与 Norris 和 Ortega (2009) 的主张相呼应，即语法复杂性应该作为一个多维结构来研究。此外，我们已经确定了现有文献用来定义语法复杂性的四个主要参数：长度、比率、索引和频率。每个参数的变化在我们的评论中都有详细的总结。最后，我们还讨论了 EAP 语境中 L2 写作教学的教学意义。我们已经确定了现有文献用来定义语法复杂性的四个主要参数：长度、比率、索引和频率。每个参数的变化在我们的评论中都有详细的总结。最后，我们还讨论了 EAP 语境中 L2 写作教学的教学意义。我们已经确定了现有文献用来定义语法复杂性的四个主要参数：长度、比率、索引和频率。每个参数的变化在我们的评论中都有详细的总结。最后，我们还讨论了 EAP 语境中 L2 写作教学的教学意义。