（一）形式 　　注：

1、在从句中，be动词多用were的形式。在口语中，如果主语是第一、第三人称单数的话，be动词可用was，但人们总是说：If I were you.。.

2、主句中的谓语可以由would，should，could和 might这四个不同的情态动词来构成。

3、与将来事实相反的条件从句中，谓语有三种不同的形式：过去式、were +to do或should +do。 　　例句1：If I were you，I would study hard.我要是你的话，我就会好好学习。（与现在事实相反） 　　例句2：If I had studied hard，I would have passed CET-6 last semester.我要是早就好好学习的话，那么我上个学期就通过六级考试了。（与过去事实相反） 　　例句3：If Iwere to pass CET-6，I would treat you to dinner at KFC.我要是过了六级考试，就请你去吃肯德基。（与将来事实相反）

（二）省略/倒装 　　如果在虚拟从句中包含有一个助动词、情态动词、动词be或have，则可把if省略，把上类动词提到主语之前，使用倒装语序。

例句4：Had it not been for the PLA，we wouldn’t have been able to beat the flood.4要不是人民解放军，我们是无法战胜洪水的。

例句5：Were he here now，he would certainly help me.5他要是在这里肯定会帮我的忙。 　　注4：例句4中的从句部分出现了否定词not，如果把该句还原成正常语序，应该是： 　　If it hadn’t been for the PLA，we wouldn’t have been able to beat the flood.

但是一旦句子发生了省略，就必须把hadn’t分开，否定词not还原，放在主语之后，不可写成Hadn’t it b

某事很可能发生，条件是可能存在的，主句中某种情况发生的概率也是很高的。如：

If you ask him,he will help you.如果你请他帮忙，他会帮你的。

If you fail in the exam,you will let him down.如果你考试不及格，你会让他失望的。

If you have finished the homework,you can go home.如果你作业做完了就可以回家了。

另外，if从句还表示不可实现的条件或根本不可能存在的条件，也就是一种虚拟的条件或假设。从句多用一般过去时或过去完成时，表示对现在或过去的一种假设。如：

If I were you,I would invite him to the party.如果我是你，我会邀请他参加聚会。

I would have arrived much earlier if I had not been caught in the traffic.要不是交通堵塞，我本会来得早一些。

另外你还要注意if 条件句的时态搭配

1.if从句用一般现在时，主句用一般将来时

If he runs he’ll get there in time.如果他用跑的，他就会及时赶到那儿。

The cat will scratch you if you pull her tail.如果你拉猫的尾巴，它就会抓你。

2.if从句用一般现在时，主句用may/might/can

If the fog gets thicker the plane may/might be diverted.如果雾在大一些，飞机可能就会改在别的机场降落。

If it stops snowing we can go out.如果雪停了，我们就可以出去。

3.if从句用一般现在时，主句用must/should

If you want to lose weight you must/should eat less bread.如果你想减肥，你必须少吃面包。

4.if从句用一般现在时，主句用一般现在时

If you heat ice it turns to water.（也可用will turn）如果把冰加热，它就会化成水。

5.if从句用现在进行时，主句用一般将来时

If you are looking for Peter you’ll find him upstairs.如果你是在找彼得，上楼就会找到他。

6.if从句用现在完成时，主句用一般将来时

If you have finished dinner I’ll ask the waiter for the bill.如果你吃完了，我就叫服务生来算账

1.His doctor suggested that he ______ a short leave of absence.

A.will take　　 B.would take　　 C.take　　 D.took

2.The job would require that ______ at 7 o'clock every morning.

A.he will be at the factory　　 B.he be at the factory

C.he was at the factory　　 　　D.he has been at the factory

3.Your advice that she ______ till next week is reasonable.

A.will wait　　 B.is going to wait　　 C.waits　 D.wait

4.The housemaster was strict.He requested that we ______ television on week nights.

A.not watch　　　　　　　　　　　　　　 B.must not to watch

C.not be watching　　　　　　　　 　　　D.have not watched

5.It is necessary that a worker ______ his work on time.

A.accomplishes　　　　　　　　　　 B.can accomplish

C.accomplish　　　　　　　　　　　 D.has accomplished

6.It is important that he ______ his decision before Friday.

A.will make　　 B.makes　　 C.make　　 D.must make

7.You look so tired. It's time you ______ 。

A.go to sleep　　　　B.went to sleep

C.go to bed　　　　　D.went to bed

8.I'd rather you ______ anything about it for the time being.

A.do　　 B.didn't do　　 C.don't　　 D.didn't

9.But for water，it ______ impossible to live in the desert.

A.is　　 B.was　　 C.were　　 D.wouldn't be

10、 ______ it______ for your help，I couldn't have made any progress.

A.Had;not been　　　　　　　　　　 B.Should;not been

C.Did;not been　　　　　　　　　　 D.Not;be

11.Long ______ the Party!

A.lives　　 B.live 　　　C.will live　　 D.should live

12.Mary insisted that Tom ______ her the ring back.

A.gives　　 B.give　　 C.given　　 D.have given

13.My suggestion was that the meeting ______ off till next week.

A.to put　　　　　　　　　　　　　　　　 B.be put

C.should put　　　　　　　　　　　　　　 D.be putting

suggested that I ______ my homework first before watching TV.

A.did　　　　 B.do　　　 C.shall do　　D.have done

15.He insisted that nothing ______ till he arrived.

A.must be started 　　　　　　　　　　　　　　　　 B.ought to be started

C.could be started 　　　　　　　　　　　　　　　　D.should be started

suggests that Ann ______ the house.

A.can sell 　　B.sells 　　　C.sell 　　 D.sold

17.It's better that he ______ it from you.

A.'ll hear 　　 B.hears　　 C.should hear　　 D.heard

18.It was necessary that he ______ about what had happened.

A.be told 　　 B.was told　　 C.should tell 　　 D.tell

19.It's astonishing that she ______ sad at news that it has nothing to do with her.

A.felt　　 B.should feel 　　C.'ll feel 　　 D.would feel

20.It was strange that we ______ short of water in the country where it was always raining.

A.are 　　 B.be　　　 C.should be 　　 D.both B and C

21.It is strange that she ______ marry such an ugly man.

A.would　　 B.should 　　　C.shall　　 D.must

22.It's not right that the meeting ______ off till tomorrow.

A.must be put　　 B.must put　　 C.will be put　　 D.be put

23.It was impossible that he ______ the train, for he had started out very early.

A.could have missed 　　　　　　　　　　　　　B.must have missed

C.should have missed 　　　　　　　　　　　　 D.should miss

24.It's a pity that he ______ such a good chance.

A.should miss B.should have missed C.has missed D.all the above

25.He tried to find some excuse for the debt, but I insisted that he ______ it off at once.

A.must pay　　 B.ought to pay 　　C.paid　　 D.pay

Ford insisted that he ______ right, though the others didn't think so.

A.should do　　 B.should have done 　　C.had done　　 D.did

27.His pale face suggested that he ______ the sad news.

A.should be told 　　　　B.should have been told

C.was told 　　　　　　　 D.had been told

28.He suggested that we ______ here at once.

A.should leave　　 B.must leave　　　 C.left 　　 D.ought to leave

29.My order is that everyone ______ their own work in time.

A.must complete　　 B.completed　　　　 C.completes 　　 D.complete

30.We've made the decision that we ______ at the school gate at 7 tomorrow morning.

A.will gather 　　　　　　B.are about to gather

C.would gather 　　　　　D.should gather

31.----I'll be waiting for you at home.

---- ______ I were busy and couldn't come?

A.What if 　　 B.What when 　　C. How if 　　D.How when

32.After he was praised for what he had done, he said，“I ______ even better under harder conditions. ”

A.would do 　　B.would have done 　　C.did 　　D.had done

33.It has been raining for a day, but even though it ______ ， we ______ there by tomorrow.

A.hadn't rained, couldn't get 　　　　B.hadn't rained, can't get

C.didn't rain, couldn't get 　　　　　D.didn't rain, can't get

34.We could not have succeeded ______ your help.

A.but for 　　　　　　　　　　　　　　　　　　　　 B.without

C.if it had not been for 　　　　　　　　　　　　 D.all the above

35.I dare say he is not your true friend, because a true friend ______ differently when you were in trouble.

A.acted 　　　B.had acted C.would act 　　D.would have acted

参考答案：

1.C 　2.B 　3.D 　　4.A 　5.C

6.C 　7.D 　8.B 　　9.D 　10.A

11.B 12.B　 13.B 　14.B

15、 D insist作“要求别人做某事”解，其宾语从句用should型虚拟语气。

16、 C 这种should型虚拟语气，有时可将should省略，因此，C项的sell不能有人称变化。

17.C 本句话有“要求”的意思，故选C。

18、 A C、D为主动，在此不妥。

19、 B 选B表示了说话人带有一种十分惊讶的感情，选A项与she的人称不相一致，是错的。参见本章语法说明。

20、 D

21.B should带有感情色彩。

22.D 本句带有要求之意，故从句谓语用should型虚拟语气。D项中的should被省略。

23.C 本句带有惊讶之意，故从句须用should型虚拟语气。但由于是过去的事情所产生的惊讶，所以用should+不定式完成式。

24.D 如选A，这表达了说话人对将来的事所发出的感叹，选B则是对已经过去的事情的感叹。选C则是一个直陈语气，即说话人对此并不一定感到十分惋惜，而是对此事的陈述。

25.D insist在作“坚持要求别人做某事”时，需要用should型虚拟语气，should也可以省略。

26.C insist在作“坚持自己的观点、看法等”解时，不需要用虚拟语气，所以A、B两项用在此处不当。D项时态不准确，故也应排除。

27.D suggest作建议解时，后接了should型虚拟语气，但在本句中作“表明”解，这时不用虚拟语气，A、B两项都应排除，C项时态不当。

28.A 在本句中suggest作“建议”解，故选A。

29.D “建议”、“命令”、“要求”等动词的名词形式做主语时，其表语从句也须用should型虚拟语气，本句中的should被省略。

30.D “建议”、“命令”、“要求”等动词的名词形式做主语时，后接同位语从句时也须should型虚拟语气。

31.A What if…？常用于省略疑问句，既可以用于虚拟语气，也可用于直陈语气。本句不省略的形式为What would you do if。

32.B 本句的under引出一个非真实的条件，当然也可以是真实条件。根据上下文，应理解为与过去事实相反，故其谓语动词用would have done。

33.B even though=even if意为“即使”。它同if一样可以引出一个真实的让步从句，也可以引出一个非真实的让步从句。根据上文，even though是一个非真实的与过去事实相反的让步从句。而主句we can't get there却是一个真实的情况。

34.D

35.D 从全句的意思分析，a true friend-differently实际上是指一种假设，而when引导的从句又告诉我们，这是一个与过去事实相反的假设，故用would have acted。

一。基本结构

1、 与现在事实相反

If + 主语+were/ did/ were doing, 主语+should/ would/ could/ might +动词原形

强调：必须把上面的结构套用对！

2、 与过去事实相反

If + 主语+ had done, 主语 +should/would/ might/ could + have done.

强调：必须把上面的结构套用对！

3、 与将来事实相反

If + 主语 + were/ did/ were to do/ should do, 主语+ should/ would/ could/ might do

强调：必须把上面的结构套用对！

第三个结构中，从句中的were to do可能性最小，should do的可能性稍大。

二。变化

1、 错综时间条件句

所谓错综，就是结构和我们的基本结构不一致，出现了从句用与过去事实相反，而主句则为与现在事实相反或与将来事实相反。

那么，我们就分别用各自的结构即可。

If + 主语+had done, 主语 +would/should/ could/ might do

再将强调结构必须正确。

我们对比下面两个句子：

If you had studied harder then, yoursituation would have been better.

If you had studied harder then, yoursituation would be better now.

注意：在错综时间条件句中，务必有明确的表示错综的时间状语，或者通过上下文能看出是时间的不同，否则，就必须按前面的基本结构套用。

2、 含蓄条件句

假设情况并不一定用条件从句来表示，而用其他方式来表示，这就是含蓄条件句了。

用without短语，分词短语，或独立主格来表示。

Without going with you last night, I wouldhave been robbed.

=If I hadn’t gone with you last night, Iwould have been robbed.

Having known each other before, we wouldn’thave fought last night.

= If we had known each other before, wewouldn’t have fought last night.

用相当于if的其他连词表示。

But that.。.要不是

Otherwise否则

He was ill, otherwise, he would have cometo meet you.

通过上下文来判断。

I would have given you more money, but Ihad little money last month.

三。虚拟条件句中的倒装

满足如下三个条件方可倒装：

必须是非真实条件句

从句中的谓语动词有were, had,should时

倒装后，省略引导词if,

Had I a lot of money, I would buy a bighouse.

=If I had a lot of money, I would buy a bighouse.

虚拟语气是一种特殊的动词形式，用来表示说话人所说的话并不是事实，而是一种假设、愿望、怀疑或推测。判断是真实条件句还是非真实条件句。只有在非真实条件句中才使用虚拟语气。通过句子意思，看假设的条件是否能够实现，能够实现是真实条件句，不能使用虚拟语气；假设的条件不能实现则是非真实条件句，要用虚拟语气。判断这个假设是与哪个事实相反。

通常有三种情况：①与过去事实相反。②与现在事实相反。③与将来事实可能相反。

I: 最基本的虚拟语气句型:

1、 虚拟现在时表示与现在事实相反的假设，其if 从句的谓语形式用动词的过去式(be 一般用were)，主句用would/ should/ could/ might +动词原形。If places were alike, there would be little need for geographers.如果各个地方都一样，就不需要地理学家了。

2、 虚拟过去时是表示与过去事实相反的假设，if 从句的谓语形式用过去完成时即had+过去分词，主句用would / should / could / might + have +过去分词。If he had known your address yesterday,he would have telephoned you.

3、 虚拟将来时是表示对将来实现的可能性很小的或不确定的假设。If从句的谓语形式用一般过去式或用were to / should +动词原形，主句用would / should/could/ might +动词原形。If he were to leave today, he would get there by Friday

4、 省略if 采用倒装语序的条件句。有时可以把含有助动词、情态动词、be或have的虚拟条件句中的连词if省去，而将had ， should, were 等词提到主语之前，即用倒装结构。If he had worked harder, he would have got through the exams.==>Had he worked harder, he would have got through the exams.If he were to leave today, he would get there by Friday.==>Were he to leave today, he would get there by Friday.If I were in your place, I wouldn’t do that.==>Were I in your place, I wouldn’t do that.

5、 有时虚拟条件句并没用if 从句表示出来，而是用介词短语(otherwise, or, without, but for)、上下文或其它方式来表示。如：We didn't know his telephone number; otherwise we would have telephoned him. Without you help, I wouldn’t have achieved so much. But for （“要不是。”的意思）your help, I would not have succeeded.

II: 虚拟语气在从句中用should的情况:

1、 在表示建议，要求，命令，想法的动词后的从句里， 用should + 动词原形， should 可以省略。 如 advise, agree, command, decide, demand, determine, grant, indicate, insist, order, prefer, propose, request, require, stipulate, suggest, urge, vote.常考到的是: suggest, advise, demand, require, propose, insist, order, request.

His doctor suggested that he (should) take short leave of absence.

The author proposed that TV (should) be turned off at least one hour every day.

2、 在表示建议，要求，命令，想法的名词后的从句里， 用should + 动词原形， should可以省略。 如 advice, decision,agreement, command, decree, demand, determination, indication, insistence, order, preference, proposal, request, requirement, stipulation etc.

It was Bill’s suggestion that everyone (should) have a map.

His suggestion was that everyone (should) have a map.

He gave us a suggestion that everyone (should) have a map.

3、 在It is/was +形容词后的that 从句中用should的结构， should 可以省略。 这类形容词常见的有: advisable, anxious, compulsory, crucial, desirable, eager, essential, fitting, imperative（绝对必要）， impossible, improper, important, natural, necessary, obligatory, possible, preferable, probable, recommended, urgent, vital etc.

It‘s natural that she (should) do so.

It is essential that we (should) tell her the news.

4、 在 lest 和 for fear that（以免），in case（以防）从句中用should, should 可以省略。

She walked quietly lest she (should) wake up her roommates.

Have your gun ready in case we should need it.

III: wish 后的 that 从句中:

1、 表示现在或将来的愿望，从句中过去式。

I wish I knew his address.

I wish I were young.

2、 表示过去没有实现或不可能实现的愿望， 从句用过去完成式或would, could, might + have + 过去分词。

I wish you had written to him.

I wish I could have slept longer this morning, but I had to get up and come to class.

3、 如果将wish改成wished, 其后that 从句中动词的形式不变。

4、 如果that 从句中用would ， 一般表示 对现状不满或希望未来有所改变或请求

I wish he would answer my letter.

I wish prices would come down.

I wish you would help me.

I wish you would stop asking silly questions.

IV: 在 It’s about/ high/ first(second, third etc)time 后的that 从句中，用过去式。表示“该是做什么的时候了”

It is about time you were in bed.

It is high time we left.

It is the first time I came here.

V: 在would rather, would sooner, would just as soon 后的that从句中，用过去式或过去完成式，表示“宁愿做什么”

I would rather he came tomorrow than today.

John would rather that she had not gone to the party yesterday evening.

VI: 在if only（“如果。就好了”的意思） 感叹句中，谓语动词与wish宾语从句的虚拟形式相同。

If only he didn’t drive so fast!（现在）

If only she had asked someone’s advice.（过去）

If only the rain would stop.（将来）

VII: 在as if / as though 从句中，表示和现在事实相反或对现在情况有所怀疑，用过去式；表示过去想象中的动作或情况， 用过去完成式。

He speaks as if he were on the spot.

She spoke to me as if I were deaf.

This device operated as though it had been repaired.

注: 1. 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.

2、 在 insist 后的从句中， 如果是坚持自己， 用陈述语气， 坚持别人做什么事情， 用虚拟语气。

She insists that she is right.

She insisted that I should finish the work at once.

虚拟语气(Subjunctive Mood)这一语法项目是各类英语考试中心测试的重点之一。虚拟语气是一种特殊的动词形式，用来表示说话人所说的话并不是事实，而是一种假设、愿望、怀疑或推测。

Ⅰ用以表示虚拟条件的虚拟语气

⒈ 用if条件从句表示的虚拟条件，是虚拟条件最普通的方式。

① 虚拟现在时表示与现在事实相反的假设，其if 从句的谓语形式用动词的过去式(be 一般用were)，主句用would/ should/ could/ might +动词原形，例如：If I were in your position I would marry her.

② 虚拟过去时是表示与过去事实相反的假设，if 从句的谓语形式用过去完成时即had+过去分词，主句用would / should / could / might + have +过去分词，例如：If it had not rained so hard yesterday we could have played tennis.

③ 大多数的虚拟条件句属于上面三种情况的一种，但并不排除存在条件和后果中，一个和现在情况相反，另一个和过去情况相反，例如：If you had followed what the doctor said, you would not have been so painful now.这个句子在高中出现频率颇高。

④ 但是，如果后果用了虚拟语气，而条件却用陈述语气，这种用法是错的。

⒉ 除了表示虚假条件外，if从句还可以表示对将来的推测，由于是将来还没有发生的，所以谈不上是真实的还是虚假的，只能说这个事情发生的可能性有多大。一般情况下，可以用陈述语气的if从句来表示对一个未来事实的推测，这个事实是完全可能发生的。If从句的谓语形式用一般过去式或用were to / should +动词原形，主句用would / should /could/ might +动词原形，例如：Jean doesn't want to work right away because she thinks that if she were to get a job she probably wouldn't be able to see her friends very often.（1996年1月四级第44题）

⒊ 有时可以把含有助动词、情态动词、be或have的虚拟条件句中的连词if 省去，而将had ， should, were 等词提到主语之前，即用倒装结构，这时候，如果出现not等否定词，否定词需放在主语后面。这种结构在口语中很少使用，但频频出现在各类考试中出现，例如：If it had not rained so hard yesterday we could have played tennis.→Had it not rained so hard yesterday, we could have played tennis.

⒋ 大多数的虚拟条件通过上面所讲的两种方法表达，但在个别句子中也可以通过介词without和介词短语but for表达，副词otherwise等表达出来。例如：We didn't know his telephone number; otherwise we would have telephoned him.（1995年6月四级第46题）值得注意的是，包含but for的句子，谓语动词必定要用虚拟形式，但包含without等短语的句子，谓语动词未必一定要用虚拟语气。

⒌ 有时虚拟条件不是明确地表达出来，而在蕴含在用but引导的从句里，于是便出现了有谓语动词是虚拟语气的主句加上谓语动词是陈述语气的but从句构成的并列复合句，例如I would have hung you but the telephone was out of order.在这样的句子里，如果主句没有用虚拟语气，或者从句用了虚拟语气，都是错的。

Ⅱ用在宾语从句中的虚拟语气

⒈ 在表示愿望的动词wish后的宾语从句中，需用虚拟语气。（wish后的that 常省略），根据主句时态，从句谓语时态相应退后一位，例如：How she wished his family could go with him.

⒉ 在具有愿望、请求、建议、命令等主观意愿的动词（desire, demand, advice, insist, require, suggest, propose, order, recommend, decide …） 后的宾语从句中需用虚拟语气。谓语动词用(should) +动词原形。值得注意的是，如果宾语从句的动词是否定的，否定词not的位置应在动词之前，而不是动词之后。例如：The head nurse insisted that the patient not be move.另外，如suggest表达“暗示”，insist表示“坚持某种说法”时，后面的从句不用虚拟语气，例如：Her pale face suggests that she is ill.或He insisted that he did not kill the boy.

除此之外，上述动词也要求用虚拟式

① 在It is+上述动词的过去分词，其后所跟的主语从句中，如It is suggested that pupils wear school uniforms.

② 在上述动词相应的名词形式作主语+连系动词，其后的表语从句中，例如His suggestion was that classed be re-scheduled.

③ 在对上述动词相应的名词进行解释的同位语从句中，如：The workers raised the demand that their pay be increased to cope with the inflation.

⒊ would (had)rather ， would sooner也用来表达主观愿望，它们之后的宾语从句中需用虚拟语气。谓语动词用过去式表示现在或将来，用过去完成式表示与过去事实相反，例如：I would rather he went right now.

Ⅲ其他形式的虚拟语气

⒈ it is +necessary等形容词后，that主语从句中虚拟形式使用，这类形容词包括necessary, important, essential, imperative, urgent, preferable, vital, advisable等，例如It is necessary that you listen to the teacher carefully.或者It is essential that you be able to pronounce every single word correctly.

⒉ 在It's (high/about) time 之后的定语从句中需用虚拟语气。谓语动词用过去式，例如It is high time that you went to school

⒊ 虚拟语气在as if / as though 引导的方式状语从句中的应用（谓语动词形式与wish后的宾语从句基本相同）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：He felt as if he alone were responsible for what had happened. 表示过去想象中的动作或情况，谓语动词用过去完成式。

⒋ 在lest 引导的状语从句中，谓语动词多用虚拟语气，（should ）+ 动词原形。例如： The mad man was put in the soft-padded cell lest he injure himself.（1998年1月四级第38题）

⒌ 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。例如： Look at the terrible situation I am in! if only I had followed your advice.