In recent studies in second language (L2) development, notably within the focus of Complex Dynamic Systems Theory (CDST), non-systematic variation has been extensively studied as intra-individual variation, which we will refer to as variability . This paper argues that variability is functional and is needed for development. With examples of four longitudinal case studies we hope to show that variability over time provides valuable information about the process of development. Phases of increased variability in linguistic constructions are often a sign that the learner is trying out different constructions, and as such variability can be evidence for change, and change can be learning. Also, a limited degree of variability is inherent in automatic or controlled processes. Conversely, the absence of variability is likely to show that no learning is going on or the system is frozen.

中文翻译：

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变异性与苹果派一样

在第二语言（L2）开发的最新研究中，特别是在复杂动态系统理论（CDST）的关注范围内，非系统变异已被广泛研究为个体内部变异，我们将其称为变异性。本文认为可变性是功能性的，是发展所必需的。我们希望通过四个纵向案例研究的示例来说明随着时间的变化，这将为开发过程提供有价值的信息。语言结构中可变性增加的阶段通常表明学习者正在尝试不同的结构，因此可变性可以作为变化的证据，而变化可以学习。同样，在自动化或受控过程中，有限度的可变性是固有的。反过来，