虚拟语气是通过特殊的谓语动词形式来表达的愿望、假设、怀疑、猜测或建议等语气，它不表示客观存在。

1、虚拟语气用于条件状语从句中

（1）表示与现在事实相反的假设，条件状语从句中的谓语动词用“过去式（be动词的过去式用were）”，而主句中的谓语动词用“would / should/ could / might + 动词原形”。如：

If I were a boy, I would join the army.
If the had time, she should go with you.

（2）表示与过去的事实相反，条件状语从句中的谓语动词用过去完成时，主句中的谓语动词则用“would / should / might / could + have +过去分词”。如：

If he had taken my advice, he would have succeeded in the competition.

（3）表示与将来事实相反，条件状语从句中的谓语动词一般过去时或should(were to) + 动词原形，而主句中的谓语动词则用would / should/could might + 动词原形。如：

If it were to rain tomorrow, the football match would be put off.

（4）当条件状语从句表示的行为和主句表示的行为所发生的时间不一致时，动词的形式要根据它所表示的时间作相应调整。如：

If they had worked hard, they would be very tired.(从句说的是过去，主句指的是现在)

以下表格是虚拟语气用于条件状语从句中时，主句和从句谓语动词的形式：

  条件状语从句 主句 与过去事实相反 had + 过去分词 should /would/could/might + have + 过去分词 与现在事实相反 一般过去时(be用were) would/should/could/might + 动词原形 与将来事实相反

一般过去时或should(were to) + 动词原形
Would/should/cold/might + 动词原形

有时侯在使用时可省略if，句子则可换成下列形式，即“were / had / should +主语”。如：

Were I a boy, I would join the army.
Had he taken my advice, he would have succeeded.
Were it not for the expense, I would go to Britain.

2、虚拟语气用于名词性从句

（1）虚拟语气在宾语从句中的运用。

①“wish + 宾语从句”表示不能实现的愿望，译为“要是……就好了”等。表示现在不能实现的愿望，从句中的谓语动词用一般过去时；表示将来不能实现的愿望，从句中的谓语动词用“would/could + 动词原形”；表示过去不能实现的愿望，从句中的谓语动词用“had + 过去分词”或“could(should) + have + 过去分词”。如：

I wish it were spring all the year round.
I wish I had known the answer.
I wish I could fly like a bird.

②在表示建议、要求、命令等的动词suggest、advise、propose、demand、require、insist request、command、order等后的宾语从句中，谓语动词用should + 动词原形或是动词原形。如：

She suggested we (should)leave here at once.
The doctor ordered she should be operated.

（2）虚拟语气在同位语从句和表语从句中的运用。
作表示建议、要求、命令等的名词advise、idea、order、demand、plan、proposal、suggestion、request等的表语从句和同位语从句，从句中的谓语动词用“（should） + 动词原形”。如：

His suggestion that we (should)go to Shanghai is wonderful.
My idea is that they (should)pay 100 dollars.

（3）虚拟语气在主语从句中的运用。
在主语从句中，谓语动词的虚拟语气用“should + 动词原形”的结构，表示惊奇、不相信、理应如此等。如：

It is necessary(important, natural, strange, etc.)that we should clean the room every day.
It was a pity (a shame, no wonder, etc.)that you should be so careless.
It will be desired(suggested, decided, ordered, requested, proposed, etc.)that she should finish her homework this afternoon.

注意：这种从句表示的是事实。如果说人对这种事实表现出惊奇的情感，就可用虚拟语气。反之，如果不表示惊奇等情感，that从句也可用陈述句语气。如：

It is pity that you can't swim.

3、虚拟语气在其他场合的运用

（1）虚拟语气在as if/as though、even if/even though等引导的表语从句或状语从句中，如果从句表示的动作发生在过去，用过去完成时；指现在状况，则用一般过去时；指将来状况则用过去将来时。如：

He did it as if he were an expert.
Even if she were here, she could not solve the problem.

（2）虚拟语气用于定语从句中。
这种从句常用于句型“It is (high)time (that) … ”中，定语从句的谓语动词用一般过去时(be用were)或should + 动词原形，意思是“(现在)该……”。如：

It's time that I picked up my daughter.
It's high time we were going.

（3）虚拟语气用在if only引导的感叹句中。如：

If only I were a bird.
If only I had taken his advice.

（4）虚拟语气在一些简单句中的运用。

①情态动词的过去式用于现在时态时，表示说话人谦虚、客气、有礼貌或语气委婉，常出现在日常会话中。如：

It would be better for you not to stay up too late.
Would you be kind enough to close the door?

②用于一些习惯表达法中。如：

Would you like a cup of tea?
I would rather not tell you.

4、精典名题导解
 
1. When a pencil is partly in a glass of water, it looks as if it _______. (NMET  95)
A.breaks    B.has broken     C.were broken      D.had been broken

解析：答案为C。本题考查的是as if 引导的让步状语从句中的语气问题，as if引导的状语从句如果与事实一致，不用虚拟语气，如果与事实相反，应用虚拟语气。题中“当铅笔的一部分浸在水中，铅笔看上去好像断了”。而实际上铅笔并未断，与事实相反，前半部分陈述是一般现在时，因而本句是对一般现在时的虚拟，用were broken。

2. I didn't see your sister at the meeting. If she ___________, she would have met my brother.(NMET   94)
A.has come      B.did come      C.came      D.had come

解析：答案为D。本题考查的是if条件句中的虚拟语气。题意是：我在会议上没看到你姐姐，故你姐姐没来。因此如果“她来了”与事实相反，前面一句交代了虚拟语气的时态是一般过去时的虚拟，所以if从句中用had+过去分词。

3. —If he ___________, he ________that food.
—Luckily he was sent to the hospital immediately.(NMET  93)
A.was warned; would not take
B.had been warned; would not have taken
C.would be warned; had not taken
D.would have been warned; had not taken

解析：答案为B。本题考查的是条件状语从句与主句表示与事实相反时虚拟语气的用法。根据下一句语境可知，他事先并没有得到警告，表示过去时间的虚拟语气，故选B。

4. If there were no subjunctive, English ______ much easier.    (NMET)
A.will be     B.would have been    C.could have been    D.would be

解析：观察题干，可知全句表达的是与现在事实相反的虚拟语气。故答案为D。

5. The guard at the gate insisted that everybody ______ the rules.    (NMET)
A.obeys    B.obey    C.will obey    D.would obey

解析：根据insist后的宾语从句谓语要用(should) do形式规律，可定正确答案是B。

6. I wish I _____ you yesterday.
A.seen    B.did see    C.had seen    D.were to see

解析：此题表与过去事实相反的原望，答案应为C。

7. —— If he _____ , he _____ that food.
   —— Luckily he was sent to the hospital immediately.    (NMET)
A.was warned;would not take    B.had been warned;would not have taken
C.wuld be warned;had not taken    D.would have been warned;had not taken

解析：从对话看，是表达与过去事实相反的虚拟语气，故答案为B。

8. Without electricity human life _____ quite different today.   (NMET)
A.is    B.will be    C.would have been     D.would be

解析：without引出一个含蓄条件句，主句表述的是与现在事实相反的虚拟语气，故答案为D。

9. When a pencil is partly in a glass of water, it look as if it _____.  (NMET)
A.breaks    B.has broken    C.were broken    D.had been broken

解析：放入水中的铅笔看上去是断的，但实际上并非如此，因此是与现在的事实相反，这时as if从句谓语要用一般过去时，故答案为C。

10. I didn he _____ , he would have said hello to me.
A.would come    B.had come    C.came    D.did come

解析：观察题目上下文，特别是第二句的主句谓语为 would have said，可知if从句表述的是与过去事实相反的愿望，因此答案为B。

11. _____ it _____ for your help, I couldn have made any progress.
A.Had;not been    B.Should;not be    C.Did;not be    D.Not;be

解析：根据主句谓语形式，可知从句要用had done形式，故应选A，Had it not been for your help＝If it had not been for your help.（要不是你帮忙的话）

12. Mr Smith was badly ill, or he _____ our dinner party.
A.should come to    B.would have attended    
C.would come to    D.should have attended

解析：or可引导含蓄条件句，表达虚拟语气。根据此题内容，可知是与过去事实相反的假设，故答案为B。