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虚拟语气在as if / as though 引导的方式状语从句中，谓语动词形式与wish后的宾语从句基本相同
1.表示与现在事实相反或对现在情况有怀疑，谓语动词用过去式。例如：
(1)、He felt as if he alone were responsible for what had happened.他感到仿佛唯独他要对发生的一切负责。
(2)、Alan talked about Rome as if he were a Roman.艾伦谈起罗马来好像他是个罗马人一样。
3John pretends as if he didn’t know the thing at all， but in fact he knows it very well.(用过去式表示与现在事实相反的假设)
2. 表示过去想象中的动作或情况，谓语动词用过去完成式。如：
(1)、The tree looked as if it ______ for a long time.
A. hasn’t watered B. didn’t water
C. hadn’t bee watered D. wasn’t watered
(2)、The old man looked at the picture， he felt as though he (go) back to time 20 years ago.
那老人看着照片，他觉得仿佛回到20年前的时光。
3.表示与将来事实相反：
(1)、They talked and talked as if they would never meet again
他们谈了又谈，仿佛他们不会再相见的样子。
注： 在as if / as though 句中， 如果有可能成为事实， 用陈述语气。
He looks as if he is going to be ill.
二：虚拟语气用在目的状语从句中
在由lest, for fear that, in case等引导的目的状语从句中需用虚拟语气，表示“以防，以免”等意思，其谓语动词多由should +动词原形构成，should也可省略; 在so that, in order that 等引导的目的状语从句中，谓语动词可用should/ might/ could加 动词原形来构成虚拟语气。
例如：
⑴、He was punished lest he should make the same mistake again.他被处以惩罚以免他再犯。
⑵、The mad man was put in the soft-padded cell lest he _____ himself.
a. injure b. injured c. had injure d. would injure
这个疯子被关进墙上装有衬垫的病房，以免伤了他自己。
3. 他拼命地干活惟恐被老板解雇。
4. The meeting will be put off, in case that it _________.
A. raining B. rained
C. rain D. shall rain
5. She stayed at home for a few days so that she might take care of her mother.
三.虚拟语气用于让步状语从句中
l 在让步状语从句中，谓语动词多用动词原形来构成虚拟语气。
E.g. 1. All magnets behave the same whether they be large or small.
所有磁铁无论大小，其性质都是一样的。
2. Whether he be rich or poor, I will marry him all the same.
无论他是富还是穷，我都要嫁给他。
倒装形式：Be he rich or poor, I will marry him all the same.
注：由even if/ even though引导的让步状语从句，其从句的谓语动词形式与含有非真实条件从句的主从句中的谓语动词一样来构成虚拟语气。
3. Even though she had been busy, she would have helped us.
即使她当时很忙，她也会帮助我们。
4. The business(业务) of each day, ( ) selling goods or shipping them, went quite smoothly.
A. it being B. be it C. was it D. it was
l whatever，whoever，whichever，whenever，however，whether，no matter what ,no matter who，no matter which.no matter how等引导的让步状语从句，当表示一种态度.应用虚拟语气，谓语动词多用may(might)+原形动词.如：
The peasants have decided to build a power station，whatever the difficulties may be.不管有什么困难农民们决定建一座电站。
Whatever he may say, I'll stand my ground.不管他说什么，我坚持我的立场。
I won't let you in whoever you may be.不管你是准.我都不让你进去。
No matter what you may say，I'm determined to do what I think is right.不管你说什么.我决心干我认为对的事情。
如从句指的是过去的事，may (might)后面要用现在完成时，如：
You mustn't be proud, however much you may have achieved.不管你取得多大的成就，你都不能骄傲。
如这样的从句所表示的是一种事实感，一种必然性时，仍用陈述语气如：
However hard it rains, we shall go home tonight.不管雨下多大，我们今晚要回去。
Whenever we met with difficulties, they came to help us.每当我们遇到困准时，他们总来帮助我们。
三：介词短语表示虚拟
有时假设的情况并不以条件从句表示出来，而是通过一个介词短语来表示，或通过上下文或其他方式表示出来。如but for， but that…， in case of， otherwise， supposing， under more favorable conditions， without 等表示让步假设。
1)、He worked very hard; otherwise he might have failed. (他刻苦工作，不然他就失败了。)
2)、We could have done better under more favorable conditions.(假设我们有更有利条件，我们还会做得更好。)
3)、 But for his help，I .
[A]should not have succeeded
[B]had not succeeded
[C]did not succeed
[D]have not succeeded
4)、 But that he came to help me， I .
[A]could not have succeeded
[B]did not succeed
[C]could not succeed
[D]can‘t but succeed
第四节：虚拟语气用在It is(about /high)time +that定语从句中
在It is(about/high)time +that定语从句中需用虚拟语气，表示“该做……的时候了”，其动词形式用一般过去时或should +动词原形。
(1)、现在5点钟了，你不认为我们应该回家了吗?
(2)、It is about time you (be) in bed.
注：
1、在this is the first time /second time that.……句型中，从句中谓语动词用陈述语气完成时态。
例如：
Is this the first time that you have visited Hong Kong?这是你第一次参观香港吗?
2、It’s time to do something有别于It’s time that.……
第五节：在if only 引起的感叹句中需用虚拟语气
谓语动词用过去式或过去完成式(谓语动词与wish宾语从句的虚拟形式相同)。
⑴、If only he didn‘t drive so fast! (现在——一般过去时)
⑵、If only she had arrived in time, she would not have been punished.(过去——过去完成时/would, could+ have done)
⑶、If only the rain would stop.(将来——would/could/might+动词原形)
only if表示"只有";if only则表示"如果……就好了"。If only也可用于陈述语气。例如：
I wake up only if the alarm clock rings. 只有闹钟响了，我才会醒。
If only the alarm clock had rung. 当时闹钟响就好了。
例题解析：
⑷、Look at the terrible situation I am in! If only I ____ your advice.
A. follow B. had followed C. would follow D. have followed
if only 引出感叹句，意思是“要是……多好”，表示说话人的一种愿望，希望发生(事实上不可能发生)与过去事实相反的情况。本句的全句意思是：“看我现在的处境多糟糕!要是我听从你的劝告多好”。事实上，句中的“我”没有听从劝告，所以处境很糟糕。
题中空格处应当用虚拟语气，答案是B
5. If only the committee ( ) the regulations and put them into effect as soon as possible.
A. approve B. will approve C. can approve D. would approve
l need "不必做"和"本不必做"
didn't need to do表示过去不必做某事, 事实上也没做。
needn't have done表示过去不必做某事, 但事实上做了。例如：
John went to the station with the car to meet Mary, so she didn't need to walk back home.
约翰开车去车站接玛丽，所以她不必步行回家了。
John went to the station with the car to meet Mary, so she needn't have walked back home.
约翰开车去车站接玛丽，所以她本不必步行回家了。 (Mary步行回家了，没有遇上John的车。)
典型例题
There was plenty of time. She ___.
A. mustn't have hurried B. couldn't have hurried C. must not hurry D. needn't have hurried
答案D。needn't have done. 意为"本不必"，即已经做了某事，而时实际上不必要。
Mustn't have done 用法不正确，对过去发生的事情进行否定性推断应为couldn't have done, "不可能已经"。 must not do 不可以(用于一般现在时)。
