一、虚拟语气概述
虚拟语气表示说话人所说的话不是事实，而是一种假设、愿望、建议或猜测。
二、if条件句的虚拟
1. 与现在事实相反
构成：If + 过去式，would/could/should/might + 动词原形
例句：If I were you, I would accept the offer.（如果我是你，我会接受这个提议。）
2. 与过去事实相反
构成：If + had done，would have done
例句：If she had studied harder, she would have passed the exam.（如果她更努力学，就通过考试了。）
3. 与将来事实相反
构成：If + should do / were to do / 过去式
例句：If it should rain tomorrow, we would cancel the trip.（万一明天下雨，我们就取消行程。）
三、wish从句的虚拟
wish + 过去式（对现在虚拟）；wish + had done（对过去虚拟）；wish + would do（对将来虚拟）
例句：I wish I knew the answer.（我希望我知道答案。）
四、as if/though的虚拟
He talks as if he were the boss.（他说话的口气好像他是老板似的。）