类   别

用   法

例   句

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+do

If he were here, he would help us.

与过去事实相反

从句动词：had+done
主句动词：should/would/could/might+have+done

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+to do主句动词：should/would/could/might+动词原形

If it should rain tomorrow, we would not go camping.

省略if的虚拟条件句

将虚拟条件从句中的were，had,should放到主语之前，构成主谓倒装

①Should he come ,tell him to ring me up.

②Were I you,I would not do it.

③Had I been free,I would have visited you.

混合虚拟条件句

不同时间的虚拟：各遵守各的规则

①If he had listened to me, he would not be in trouble now.

②If he had told me yesterday,I should know what to do now.

③If I were you, I would have gone to her birthday party.

虚拟与陈述的混合：各遵守各的规则

①He could have passed the exam,but he wasn’t careful enough.

②You should have come earlier.The bus left a moment ago.

含蓄虚拟条件句

but for+名词表示虚拟条件

句子或主句中的谓语动词的形式视具体情况而定。这是考查考生应变能力的最佳试题。

---But for your timely warning,we ______ into great trouble.

---You know we’re friends.

A. would get          B. must have got   

C. would have got      D. can’t have got

without+名词表示虚拟条件

Without the air to hold some of the sun's heat, the earth at night would be freezing cold.

动词不定式表示虚拟条件

It would be only partly right to follow in this way.
如果用这种方式，仅仅对了一半。

现在分词表示虚拟条件

Having known in time ,we might have prevented the accident.要是及时得知的话，我们也许能阻止这场事故。

过去分词表示虚拟条件

Given more attention, the tree could have grown better.
如果多留心的话，这树本来可以长的更好。

副词otherwise表示虚拟条件

I was too busy at that time.Otherwise,I would have called you.我当时太忙，否则我就给你打电话了。

连词but连接的句子表示虚拟条件

He _____fatter but he eats too little .

A. would become      B. would have become 

C. must become       D. must have become

其它状语从句

as if/as though引导的状语从句中动词用did或had＋done或would／could／might＋do。

注意：as if/as though引导的状语从句中也可以用陈述语气：

当说话者认为所述的是真实的或极有可能发生或存在的事实时：

It sounds as if it is raining．听起来像是在下雨。
He talks as if he is drunk．从他谈话的样子来看他是醉了。

①与现在事实相反

He talks as if he knew where she was．

②与过去事实相反

He talks about Rome as if he had been there before.

③与将来事实相反

He opened his mouth as if he would say something.

in order that/so that引导的状语从句中动词用can/could/may/ might/ would等+do

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+do

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+do表示与现在，过去和将来情况相反

I wish I could be a pop singer.

I wish I would have gone to Shanghai last month.

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+do

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+do

It’s high time that we left/should leave.

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!