祈使语气 (imperative mood),表示所说的话是请求或命令。
If it doesn’t rain tomorrow, I will go for a picnic. 假若明天不下雨，我就去野餐。
Oil floats if you pour it on water. 你如把油倒在水里，油就浮起来。
If 主语 +动词过去式（be的过去式用were）
should （would, might， could）+动词原形
If 主语 +had+过去分词
should （ would, might， could）+ have ＋过去分词
If 主语 +动词过去式（be的过去式用were）； should＋动词原形；were to＋动词原形
should （would, might， could）+动词原形
1. 与现在事实相反的虚拟条件句，条件从句的谓语用动词的过去式 (be的过去式用were), 主句的谓语用should （would, might， could）+动词原形。
If it were not raining, we should go for a picnic.如果现在不下雨的话，我们就出去野餐了。
If he came here, he might be able to help you. 如果他来这，他就能够帮助你了。
2. 与过去事实相反的虚拟条件句，条件从句的谓语用had+过去分词，主句的谓语用should （ would, might， could）+ have ＋过去分词。
如： She would have gone to the party if she had been invited.
If she hadn't called me, I would have overslept this morning.
3. 与将来事实可能相反的虚拟条件句，条件从句的谓语用动词的过去式(be的过去式用were)； should＋动词原形；were to＋动词原形，主句用should （would, might， could）+动词原形。
如： If I were to be twenty years old next year, I would take the course of French.
If it should fail, I would try again.要是失败了，我会再试一次。
如： If we caught the early train, we’d get there by lunch time.
If we missed the train, we should have to wait an hour at the station.
He would pass the test if he had taken my advice．如果他听了我的劝告，他现在会通过考试。
If I had spoken to him yesterday, I should know what to do now.
You would be much better now if you had taken my advice.
如条件从句用if I were...，主句则可用表任何时间的虚拟形式。
如： If I were not busy, I would have come.
If I were you, I would go.
Had you not helped me， I should have failed.要是没有你的帮助，我就失败了。
Were you in my position, you would do the same. 假如你处在我的地位，你也会这样干的。
Should they attack us, we’ll wipe them out completely.
如： But for your help we couldn’t have succeeded in the experiment.
如果没有你的帮助，我们的实验是不会成功的。(暗含在分词短词but for your help)
What would I have done without you? 如没有你，我会怎么办呢？(条件暗含在介词短语without you 中)
It would be easier to do it this way. 这样做会比较容易。
(条件暗含在不定式短语 to do it this way中)
This same thing, happening in wartime, amount to disaster.
同样的事，如发生在战时，就会酿成大祸。(条件暗含在分词短语happening in wartime 中)
He must have the strength of a hippopotamus, or he never could have vanquished that great beast. 他一定是力大如河马，否则他绝不会击败那只庞大的野兽。(暗含条件是连词or)
Alone, he would have been terrified. 如是单独一人，他是会感到害怕的。(暗含条件是alone)
如： You might stay here forever. 你可以永远待在这儿。(可能暗含if you wanted to)
We would have succeeded. 我们本来是会成功的。(可能暗含if we had kept trying)
Your reputation would be ruined. 你的名誉会败坏的。(可能暗含 if you should accept it)
如： You wouldn’t know. 你不会知道。
I would like to come. 我愿意来。
虚拟条件句中的条件从句除用if引外，还可用when, unless, lest, suppose, as if, for fear, in case, on condition 等词语来引导。
如： The peasants prepared to feed the city when it should be freed.
Lest you should not have heard all, I shall begin at the beginning.
Unless I were well, I wouldn’t be at school. 除非我好了，否则我不会上学。
Suppose you were given a chance to study in America , would you accept?
假如给你一个到美国学习的机会，你会接受吗？（suppose 或 supposing =what if）
Supposing it were so？（=Supposing it were so，what would happen？）
He can use the bicycle on condition that he should return it tomorrow.
In case I forget , please remind me of my promise 如果我忘了，请提醒我的诺言。
Susan is walking slowly ,as if she were tired. 苏珊走得很慢，就像是累了似的。
“常用在It is (was)+形容词 / 过去分词+that引导的主语从句”的句型中的主语从句要用虚拟语气。主语从句的谓语用should+动词原形(或should+have+过去分词)或只用动词原形(尤其是美国英语)。should在此是助动词，本身并无实义，这种主语从句中的should有时有感情色彩。
It's important that we（should）work out a plan. （带有“要求”的含义）
It's better that he go at once. （带有“建议”的意思）
☆ 用于本句型的形容词并不多，常见形容词有：necessary，important，best, right, impossible，preferable，desirable, imperative, advisable，essential，reserved，urgent， 等。
It is necessary that he（should）be sent there at once．
It's strange that he should say so.
I was glad that he should go.
It is important that we should speak politely.
It is a pity that she should fare so badly.
It's right that you should think that way.
☆用于本句型中的过去分词就是表示提议要求、命令等动词的过去分词，如suggested，settled, required，requested，demanded，urged，decided, proposed，ordered，desired，advised等。
It is requested that Professor Liu（should）give us a lecture．
It is desired that we（should）get everything ready by tonight．
I’m ashamed you should have done such a thing.
It has been suggested that the meeting（should）be put off．有人建议推迟会议。
It is settled that you leave us, then?
注意：这种句型中的主语从句也可用陈述语气，如：It was important that he made an explicit statement on this score last week. 他上个星期对于这一方面做了明确的说明，这是很重要的。
1). 宾语从句在表示提议、要求、命令、意志等动词后，其谓语用should+动词原形或只用动词原形的虚拟语气，作为suggest，request，demand，urge，propose，prefer，advise，insist，require，order，command，maintain，ask，object, arrange, desire等动词的宾语。
The doctor suggested that he not go there．医生建议他不要去那里。
He suggested that we should leave early. 他建议我们早点动身。
The judge ordered that the prisoner should be remanded. 法官命令被告还押。
I wish it were true．我但愿这是真的。
I wish you would stay a little longer.我希望你再待一会儿。
☆ 表示无能为力的过去愿望（与过去事实相反），可用“had +过去分词”或“could（would，might）+have+过去分词”
I wish you had called yesterday．我希望你昨天来过电话。
We wish you had come to our New Year’s party.我们真希望你来参加了我们的新年联欢会。
3). would rather, would sooner等表示愿望，其宾语从句常用虚拟过去式。
☆ 用过去完成式(had + 过去分词)表示过去事实相反的含义
I would rather you came tomorrow.我宁愿你明天来。
I’d sooner she left the heavy end of the work to some one else.我宁愿她把重活留给别人。
4). 有些动词，如think, expect, believe,其否定式的宾语从句亦可用should+动词原形。如：
I never thought he should refuse.我万没有想到他会拒绝。
She did not expect that you should come.她没有预料你会来。
My suggestion is that we (should) send a few soldiers to help them.
My advice is that you (should) treat her well. 我的忠告是你应该善待她。
He makes the demand that she (should) leave the place at once.
My suggestion is that we should tell him.我的建议是我们应该告诉他。
Our only request is that this should be settled as soon as possible.
如：There was a suggestion that Brown should be dropped from the team.有一项建议是布朗应该离队。
常用在It is time (that)…句型中，定语从句常用虚拟过去式
It is time the children went to bed. 孩子们早该上床睡觉了。（表示催促）
It's high time that he began to think how to deal with money.
It is time we left.我们该走了。
It is time we went to bed.我们该去睡觉了。
Long live the Communist Party of China！中国共产党万岁！
God bless you! 上帝保佑你。
God damn it! 该死的！
The devil take you! 见鬼去吧！
So be it then. 就那样吧。
It is important that he should know about this.他必须知道此事。
It was important that he should know about this.他必须知道此事。
I suggest that we should go tomorrow.我建议我们明天走。
I suggested that we should go the next day.我建议我们第二天走。
She said, “If I were a boy I would join the army.”她说，“我如是男孩，就参军。”
She said that if she were a boy, she would join the army.她说她如是男孩就参军。
“If I knew how it worked, I could tell you what to do,” he said.
He said that if he had known how it worked he could have told me what to do.
“If I knew the answer to all your questions I'd be a genius,” he said.
He said that if he knew the answer to all my questions, he’d be a genius.
如：I would think he was wrong.我看他是错了。(须用was,试比较：I think he is wrong)
It would seem that she was right. 她似乎是对的。(须用was,试比较：It seems that she is right)
1.I enjoyed the movie very much. I wish I _____ the book from which it was made.
A. have read B. had read
C. should have read D. are reading
2.You are late. If you _____ a few minutes earlier, you _____ him.
A. come; would meet B. had come; would have met
C. come; will meet D. had come; would meet
3.The two students talked as if they _____ friends for years.
A. should be B. would be
C. have been D. had been
4.It is important that I _____ with Mr. Williams immediately.
A. speak B. spoke
C. will speak D. to speak
5.He looked as if he _____ ill for a long time.
A. was B. Were C. has been D. had been
6.If the doctor had come earlier, the poor child would not _____.
A. have laid there for two hours B. have been lied there for two hours
C. have lied there for two hours D. have lain there for two hours
7.I wish that I _____ with you last night.
A. went B. could go
C. have gone D. could have gone
8.Let’s say you could go there again, how _____ feel?
A. will you B. should you
C. would you D. do you
9.I can’t stand him. He always talks as though he _____ everything.
A. knew B. knows
C. has known D. had known
10._____ the fog, we should have reached our school.
A. Because of B. In spite of
C. In case of D. But for
11.If you had told me in advance, I _____ him at the airport.
A. would meet B. would had met
C. would have met D. would have meet
12.Mike can take his car apart and put it back together again. I certainly wish he_____ me how.
A. teaches B. will teach
C. has taught D. would teach
13.I would have told him the answer, had it been possible, but I _____ so busy then.
A. had been B. were
C. was D. would be
14.He’s working hard for fear that he _____.
A. should fall behind B. fell behind
C. may fall behind D. would fallen behind
15.If it _____ another ten minutes, the game would have been called off.
A. had rained B. would have rained
C. have seen D. rained
16.He suggested that they _____ use a trick instead of fighting.
A. should B. would
C. do D. had
17.My father did not go to New York; the doctor suggested that he _____ there.
A. not went B. won’t go
C. not go D. not to go
18.I would have gone to the meeting if I _____ time.
A. had had B. have had
C. had D. would have had
19.Would you rather I _____ buying a new bike?
A. decided against B. will decide against
C. have decided D. shall decide against
20.You look so tired tonight. It is time you _____.
A. go to sleep B. went to sleep
C. go to bed D. went to bed
21.—Why didn’t you buy a new car?
—I would have bought one if I _____ enough money.
A. had B. have had
C. would have D. had had
22.If she could sew, _____.
A. she make a dress B. she would have made a shirt
C. she will make a shirt D. she would had made a coat
23._____ today, he would get there by Friday.
A. Would he leave B. Was he leaving
C. Were he to leave D. If he leaves
24.His doctor suggested that he _____ a short trip abroad.
A. will take B. would take
C. take D. took
25.The Bakers arrived last night. If they’d only let us know earlier,_____ at the station.
A. we’d meet them B. we’ll meet them
C. we’d have met them D. we’ve met them
26.If I _____ you, I _____ more attention to English idioms and phrases.
A. was; shall pay B. am; will pay
C. would be; would pay D. were; would pay
27.We might have failed if you _____ us a helping hand.
A. have not given B. would not give
C. had not given D. did not give
28.The law requires that everyone _____ his car checked at least once a year.
A. has B. had
C. have D. will have
29.It is strange that he _____ so.
A. would say B. would speak
C. should say D. will speak
30.Had I known her name, _____
A. or does she know mine? B. and where does she live?
C. she would be beautiful. D. I would have invited her to lunch.
31.He has just arrived, but he talks as if he _____ all about that.
A. know B. knows
C. known D. knew
32.If I _____ the money, I would have bought a much bigger car.
A. possessed B. owned
C. had D. had had
33.He was very busy yesterday; otherwise, he _____ to the meeting.
A. would come B. came
C. would have come D. will come
34.The librarian insists that John _____ no more books from the library before he returns all the books he has borrowed.
A. will take B. took
C. take D. takes
35.I left very early last night, but I wish I _____ so early.
A. didn’t leave B. hadn’t left
C. haven’t left D. couldn’t leave
36.I do not have a job. I would find one but I _____ no time.
A. had B. didn’t have
C. had had D. have
37.I wish that you _____ such a bad headache because I’m sure that you would have enjoyed the concert.
A. hadn’t B. didn’t have had
C. hadn’t had D. hadn’t have
38.He insisted that we all _____ in his office at one o’clock.
A. be B. to be
C. would be D. shall be
39.Helen couldn’t go to France after all. That’s too bad. I’m sure she would have enjoyed it if _____.
A. she’s gone B. she’ll go
C. she’d gone D. she’d go
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
14．Mother 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
16．Tom 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
26．Mr. 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
1—5 BBDAD 6—10 DDCAD 11—15 CDCAA 16—20 ACAAD
21—25 DBCCC 26—30 DCCCD 31—35 DDCCB 36—39 DCAC
4.It is important that是主语从句的虚拟语气，从句用sb. should do的形式。
7.could have done表示“本来可以”。
14.for fear that后面的状语从句用sb. should do的形式。
16.suggest后面的宾语从句用sb. should do的形式。
17.suggest后面的从句用sb. should do的形式，should可以省略。
19.would rather的宾语从句用sb. did的形式。
20.It is time后面的定语从句用sb. did的形式。
22.would have done是过去将来完成时，表示与过去相反的虚拟语气。
24.suggest后面的从句用sb. should do的形式，should可以省略。
28.require后面的从句用sb. should do的形式，should可以省略。
29.It is strange that是主语从句的虚拟语气，从句用sb. should do的形式。
30.had I known是与过去相反的虚拟语气的倒装形式。
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。
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。
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。
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。