1.虚拟语气在条件状语从句中的应用
虚拟语气用在条件状语从句中，通常从句由if 引导。英语中的条件句分两种：
真实条件句：满足了某个条件就真会有这种情况发生.
如If I have time, I will go.
虚拟条件句：是虚拟假设的.虚拟条件句从时间上又分为三种：
(1)与现在事实相反的假设
条件状语从句构成：If+一般过去时(be动词用were，不用was。)
主句构成：主语+would/should/could/might+动词原形
如If I were you, I would refuse to go there.如果我是你，我将拒绝去那儿。
(2)与过去事实相反的假设
条件状语从句构成：If+过去完成时have done
主句构成：主语+would/should/could/might+have+过去分词
如If he had come yesterday,I should/would have told him about it.如果他昨天来的话，我会把这件事告诉他的。
(3)与将来事实可能相反的虚拟条件句
条件状语从句构成：一般过去时did
If+主语+were+to do
If+主语+should+do
主句构成：主语+would/should/could/might+动词原形
如We would stay at home , if it should rain tomorrow.明天要是下雨的话我们就呆在家。
We would stay at home, if the rain were to go on tomorrow.
(1)如果条件从句中含有助动词、情态动词、be动词或动词to have,可以省略if,然后倒装(把上述几种动词放在主语之前)。
如Should it rain,the crops would be saved.假如下雨，庄稼就有救了。
(2)条件从句可以用介词短语(without、but for)来代替。
如：
We couldn’t have achieved so much without your help.要不是你的帮助，我们是不能取得这样大的成就。(without your help变成从句时相当于if you had not helped us)
But for your help，we couldn’t have achieved so much.(but for 放在句首)
