高中英语虚拟的用法说明
If引导的'条件从句
与现在事实相反
从句动词：过去式（be用were）
主句动词：should/would/could/might+动词原形
If he were here, he would help us.
与过去事实相反
从句动词：had+过去分词
主句动词：should/would/could/might+have+过去分词
If I had been free, I would have visited you.
与将来事实相反
从句动词：过去式/ should+动词原形/ were+不定式
主句动词：should/would/could/might+动词原形
If it should rain tomorrow, we would not go camping.
其它状语从句
as if引导的状语从句中动词用过去式或过去完成式
They are talking as if they had been friends for years.
in order that / so that引导的状语从句中动词用can / could / may / might / would等+动词原形
Turn on the light so that we can see it clearly.
宾语从句
demand, suggest, order, insist后接的从句中动词为should+动词原形
He suggested that we not change our mind.
wish后的从句中分别用过去式，过去完成式和should/would+动词原形表示与现在，过去和将来情况相反
I wish I could be a pop singer.
主语从句
在It is necessary / important / strange that…, It is suggested / demanded / ordered / requested that…等从句中，谓语动词用should+动词原形
It is strange that such a person should be our friends.
其它句型中
It is time that…句型中动词用过去式或should+动词原形
It’s high time that we left.
would rather所接的从句中动词用过去式或者过去完成式
I would rather you stayed at home now.
If only句型中动词常用过去式或者过去完成式，表示强烈的愿望
If only our dream had come true!
