核心规则
虚拟语气用形式上的时间“后移”表达与现实的距离，或用动词原形表达建议、命令和必要性。它关注说话人对事实性的判断，不只是事件发生的时间。
结构与例句
| 情形 | if 从句 | 主句 |
|---|---|---|
| 与现在相反 | did / were | would/could/might do |
| 与过去相反 | had done | would/could/might have done |
| 将来可能性很低 | should do / were to do | would/could/might do |
愿望结构：I wish I knew the answer；I wish I had studied harder。
使用场景
suggest、recommend、insist、demand、request 等表示建议或要求时，that 从句常用 (should) + 动词原形。同类形式也见于 suggestion、essential、necessary 等名词或形容词后的从句。
常见错误
错误： If I would know, I would tell you. → 正确： If I knew, I would tell you。
错误： I wish I can fly. → 与现在现实相反通常写 I wish I could fly。
易混知识点
insist 表“坚持要求”时用虚拟形式；表“坚持认为某事实”时按真实时态：He insisted that she (should) apologize；He insisted that he was innocent。
总结
先判断是假设距离还是建议要求，再根据参照时间选择过去式、过去完成式或动词原形。
提高类 · 条件句、愿望与建议结构
高中学习重点
混合虚拟条件句的从句和主句指向不同时间：If I had taken the advice then, I would be better prepared now。含蓄条件可由 without、but for、otherwise 等表达：Without your help, we could not have finished。
would rather + 从句 表现在或将来的愿望时从句常用一般过去时，表过去遗憾时用过去完成时：I'd rather you came tomorrow；I'd rather you had told me earlier。
小练习
- 填空：If I ___ (know) about the change yesterday, I would have adjusted the plan.
- 填空：The doctor recommended that he ___ (rest) for a week.
- 改写：Without your reminder, I would have forgotten.（使用 if）
参考答案
had known。(should) rest。- If you had not reminded me, I would have forgotten。