语法不仅表达事件，也管理已知信息、新信息和对比焦点。倒装、分裂句和前置结构会改变突出对象，却不必改变基本事实条件。
为什么作者不总用普通主谓顺序？如何区分真正的语法倒装与单纯把长成分放到句首？我们要读出信息包装。
It is X that... 用分裂句把 X 设为排他或对比焦点。What...is X 用伪分裂句先建立问题槽，再给出焦点答案。The second experiment revealed the mechanism.
中性顺序把 second experiment 设为起点，把 mechanism 作为较新的结果。
It was the second experiment that revealed the mechanism.
分裂句聚焦“第二次实验”，常排除第一次实验或其他来源。
What the second experiment revealed was the mechanism.
伪分裂句把“揭示了什么”设为待填槽，焦点落在 mechanism。
Only after the data were reweighted did the pattern disappear.
限制性成分前置触发倒装，并强调消失只发生在重新加权之后。
Rarely do observational studies eliminate every alternative explanation.
否定倾向副词前置触发倒装，突出这种情况罕见。
This limitation was acknowledged by the authors.
被动让 This limitation 延续前文话题，把 authors 放在较后位置。
Particularly important is the distinction between prediction and explanation.
表语前置，主语后置；作者先给评价，再引出较长的新信息。
As for external validity, the evidence remains limited.
话题框架前置，限定接下来判断只涉及 external validity。
Many explanations could fit the observed pattern. What distinguishes the causal account is not its ability to reproduce the data, since several accounts can do that. It is the set of additional predictions that provides a stronger test. Only when those predictions are examined can the explanations be meaningfully compared.
伪分裂句先回答“因果解释凭什么不同”，分裂句再聚焦额外预测，最后倒装强调比较成立的必要条件。信息结构与论证结构在这里完全一致。
训练语境：学术科研
普通句 The interaction term matters 改为聚焦 interaction term。
可写 It is the interaction term that matters. 分裂句把 interaction term 设为对比焦点，通常暗示不是主效应或其他项。
训练语境：学术科研
解释倒装：Not until the final wave did attrition become severe.
Not until... 前置触发 did attrition become。焦点是严重流失出现得晚，在最终一轮之前并未达到严重程度。
训练语境：学术科研
为何使用被动：The hypothesis was tested in three samples.
若段落话题是 hypothesis，被动保持该话题在句首，并把新信息“在哪些样本测试”置后。主动并非总更清楚。
训练语境：学术科研
What matters is whether the effect replicates 的焦点是什么？
焦点是 whether the effect replicates 这一问题。What matters 先建立“重要内容”的空槽，后部给出答案。
训练语境：学术科研
分析：So large was the uncertainty that no precise conclusion was possible.
程度表语前置形成强调倒装，相当于 The uncertainty was so large that...。前置把不确定性的程度设为结果原因的焦点。
训练语境：学术科研
解释：The estimate did change after reweighting.
陈述句中的助动词 did 带强调，常用于纠正“没有改变”的预期。事实仍是过去改变，但立场更具对比性。
训练语境：真实生活
比较 Maya broke the vase 与 It was Maya who broke the vase。
普通句报告事件；分裂句聚焦施事 Maya，常用于回答“是谁”或纠正对人的错误判断。
训练语境：真实生活
解释：Here comes the bus.
地点副词前置并让完整名词主语后置，用于现场呈现新出现对象。代词通常不这样倒装，如 Here it comes。
训练语境：真实生活
As for the rent, we can discuss it tomorrow 做了什么？
As for 建立局部话题框架，把 rent 与其他事项分开。句子只承诺明天讨论租金，不自动推及维修或合同。
训练语境：真实生活
修正：Never I have seen such a long line.
应写 Never have I seen...。句首否定副词要求助动词位于主语之前；完成时助动词 have 直接参与倒装。
Many studies report that students benefit from feedback. Less often discussed is the order in which that feedback becomes useful. In the first stage, students may need comments that identify errors; only later do they benefit from comments that challenge the assumptions behind their solutions. What matters, then, is not feedback in the abstract but the fit between a learner's current representation of the problem and the kind of response the teacher provides.
not... but... 把主题从抽象反馈转向匹配关系。Less often discussed is... 是信息结构调整，正常语序可还原为 The order... is less often discussed。In the first stage 与 only later 构成时间对比。comments that identify errors 与 comments that challenge... 是两类反馈。What matters 是主语从句，把真正重要的内容推迟到 is 后展开。高阶语境：学术科研
第二句为什么采用倒装，而不写成 The order... is less often discussed？
倒装把 Less often discussed 放到句首，形成“从已有共识转向被忽视问题”的信息推进。它不仅改变语序，也改变读者注意力：重点不再是反馈有用，而是反馈何时有用。
高阶语境：学术科研
最后一句中 not feedback in the abstract but the fit... 的论证功能是什么？
它排除一个过宽的概念“抽象的反馈”，改为强调具体匹配关系。作者不是问反馈有没有用，而是问学生当前理解状态和教师回应类型是否匹配。
高阶语境：真实生活
用 What matters is not... but... 写一句关于学习方法的表达。
可以写：What matters is not the number of hours you study but the quality of attention you bring to each problem. 结构把表面指标排除，突出真正变量。
把异常语序还原为中性句，再问原句把哪个成分移到焦点位置、排除了什么替代项，以及这种突出如何服务段落论证。