过去虚拟语气主要用于表达与过去事实相反的假设、愿望或遗憾。其结构为：

条件句：If + 主语 + had + 过去分词

主句：主语 + would/could/might/should + have + 过去分词

与过去事实相反

- If I had known you were coming, I would have cleaned the house.

（如果我早知道你要来，我就会打扫房子）

- If he had studied harder, he would have passed the exam.

（如果他学习更努力，他就能通过考试）

表达遗憾或建议

- If only I had called you last night!

（要是我昨晚给你打了电话就好了）

- This project could have been better with more planning.

（如果规划更周密，这个项目会更好）

条件句省略

- 与现在事实相反：省略条件句中的"had"，直接用过去式

- If I had money now, I would buy a house.

- 与过去事实相反：条件句完整

- If the meeting had started on time, we wouldn't have been late.

注意：

过去虚拟语气不用于表达与现在或将来事实相反的情况，这类情况需用现在虚拟语气（If + 主语 + 动词过去式）或将来虚拟语气（If + 主语 + 动词过去式/were to + 动词原形）。