（一）在主語從句中

1. 用于It is advisable/ odd/ desirable/ imperative/ natural/ natural/ necessary/ strange/ unusual, etc. + that 引導的主語從句中。
It is highly desirable that a new president (should) be appointed for the college.

2. 用于It is desired, it is suggested, etc. +that 引導的主語從句中。
It is urged that he(should) be trained.
It is requested that Mr.Wang(should)give a performance at the party.

（二）虛擬語氣用于下列動詞后的賓語從句中

advise　　arrange　　move(提議)　　beg　　demand　　deserve
desire　　determine　　recommend　　ask　　insist　　order
prefer　　propose　　requite　　wish　　urge　　suggest
suppose　　decide

I asked that I (should) be allowed to read whatever I liked.
She move/ suggested that the meeting (should) be continued after lunch.
如果賓語從句中的動詞是否定的，從句后應是not + 動詞原形。
The doctor suggested that he not smoke.

(三) 除了wish表愿望外，還可以用在would rather, had better, would as soon 結構的賓語從句中。

I would rather you come tomorrow.
I would rather you came today.
I would rather you had come yesterday.
I would just as soon you didn’t speak rudely to her.

(四) 虛擬語氣用在條件狀語從句中

1.當非真實條件句中謂語動詞含有 should, had 或 were 時，有時可以省略if，采用倒裝結構，即將should, had 或 were 移到主語前面。如：
Should you change your mind, let me know.
Were there no gravity, there would be no air around the earth.
Had they acted sooner, the strike wouldn’t have happened.

2. 有時主句和從句中的動詞形式不一致。比如主句為 should/would/could + 動詞原形（指現(xiàn)在），而從句為had + 動詞的過去分詞（指過去）；從句為 should + 動詞原形，主句用陳述語氣或祈使句。這稱作錯綜虛擬語氣。
You would be happier now if you had taken his advice.
If you were in better health, we would have allowed you to go boating with us.

3. 有時句子中未出現(xiàn)條件句，而是由一些短語提供假設的情況。
He would have come to your party, but he was busy.
With his help, you would have succeeded in it.
But for the rain, we should have had a pleasant journey.
Without your advice, I couldn’t have done it so quickly.

4. if it were not for 表示與現(xiàn)在或將來相反，If it hadn’t been for表示過去事實相反。
Were it not for the air, all plants should die.
If it hadn’t been for your help, I really don’t know what I’d have done.

5.虛擬語氣用于It’s(high, about)time + that 的定語從句中，表示現(xiàn)在和將來，不表過去。that 從句中的謂語應用過去時（be 常用were或should/had better/had rather + 動詞原形），有時可用一般時或進行時表示委婉的建議、命令等。
It’s high time that he washed his dress.
I’m getting tired – It’s time we went to bed.
It’s about time we were going.

6. 用于 if only 含有“但原（愿）”，“要是…就好了”。其用法wish基本相同。
If only he know（had known） how we missed him!
If only he were alive.
If only I hadn’t made such a mistake!

7. 用于otherwise 或or 引導的并列句中。
I don’t know where he is, otherwise(or) I would telephone him.

8. 用在lest, in order that, in case引導的目的狀語從句中。
He told his wife as little as possible, lest she (should) spread the news all over town.

9. 用在as if, as though引導的方式狀語從句中。
She spoke to me as if I were deaf.(表同時或之后發(fā)生)
She behaved as if nothing had happened.(表從句動作在主句動作之前發(fā)生)

Exercise 6.1
1. ______, I would take an umbrella with me.
A. Had I been you           B. were I you
C. I were you                   D. I had been you
2. Had she been given some information, she ______ the question.
A. can answer                      B. can have answered
C. could have answered      D. could answer
3. I had hoped that she ______ a doctor, but she wasn’t good enough at science.
A. will become     B. became     C. would become    D. becomes
4. I’d rather you ______ with him.
A. didn’t interfere                        B. don’t interfere
C. should not interfere                  D. would not interfere
5. The job would require that ______ at seven 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
6. I’d just as soon ______ those important papers with you.
A. that you won’t take                  B. you not taking
C. don’t you take                          D. you didn’t take
7. You looked so tired tonight. It is high time you ______.
A. go to sleep            B. went to sleep          C. go to bed         D. went to bed
8. I wish I ______ to talk this over with him when he was here last night.
A. was able               B. were able               C. had been able        D. should be able
9. It was ordered ______ put in order.
A. the classroom be                    B. that the classroom be
C. the classroom to                    D. that the classroom was
10. The Reform Club proposed that wages ______.
A. would be raised                      B. be raised
C. were raised                             D. would have been raised
11. Your advice that she ______ till next week is reasonable.
A. will wait                 B. is going to wait       C. waits         D. wait
12. He felt as if he ______ more time to study for the test.
A. needs                     B. were needed          C. needed      D. need
13. Jane appears as though she ______ the secret.
A. knows                   B. knew                      C. had known    D. has known
14. Supposing Tom ______, what would you do then?
A. never come                              B. never comes
C. shall never come                      D. will never come
15. Without your help, we ______ so much.
A. will not achieve                         B. didn’t achieved
C. don’t achieve                          D. would not have achieved
16. She listened carefully ______ she might discover exactly what she wanted.
A. so as that       B. in case    C. in order     D. providing
17. It is imperative ______.
A. that you shall finish it in time       B. that you must finish it in time
C. that you could finish it in              D. that you finish it in time
18. If I had had a bike, I ______ it to you yesterday.
A. had lent         B. lent        C. would have lent       D. lend
19. I was ill that day. Otherwise I ______ part in the parade
A. should take                B. would have taken     C. took         D. would take
20. Please take a message ______ he call. (… if he should call.)
A. may      B. shall      C. should       D. will

Exercise 6.2
1. Isn’t it about time you _____ to do the work?
A. start      B. come   C. begin     D. began
2. If only we _____ a phone! I’m tired of lining up outside the public phone box.
A. have         B. had         C. will have     D. are to have
3. It is required that all members _____ present.
A. can be       B. will be      C. be              D. are
4. A: I’ll pay you by cheque monthly.
B: I’d rather you _____ me cash weekly.
A. pay            B. will pay      C. are to pay    D. paid
5. We strongly urge that you _____ interfere in this matter.
A. don’t         B. won’t        C. not            D. are not going to
6. I didn’t know his telephone number; otherwise I _____ him.
A. telephoned                  　　　　　B. had telephoned
C. would have telephoned              D. was telephoning
7. Had she been given some information, she _____ the question.
A. would answer                        　　B. could answer
C. could have answered                　D. answered
8. We hung out a lantern lest he _____ lost in the mist.
A. gets        B. should get       C. will get     D. got
9. It is best that you _____ your trip at once.
A. cancel         B. canceled      C. will cancel     D. are to cancel
10. I feel very uncomfortable. I wish I _____ so much.
A. do not eat   B. did not eat   C. had not eaten   D. have not eaten
11. It is essential that he _____ the dentist at once.
A. sees    B. see    C. will see     D. is to see
12. The committee proposed that a lawyer _____ consulted regarding their legal rights.
A. were     B. was   C. be   D. to be
13. I could go myself but I would sooner you _____.
A. go    B. have gone     C. will go    D. went
14. His hair is very long. His parents wish he _____ it cut.
A. will have      B. has      C. had       D. would have
15. The law requires that everyone _____ a test for a driver’s license.
A. takes       B. will take     C. took     D. take
16. If the waters of the ocean _____ moved away, the sea floor with its wide valleys, uneven mountains and submarine rivers would be an unbelievable sight.
A. is      B. can      C. may be     D. could be
17. If we did not have atmospheric pressure, we _____ automobile tires.
A. can not have          B. could not have
C. will not have           D. are not having
18. _____ electronic computers not been used, it would have taken them a long time to solve the complicated problem.
A. Had        B. Have        C. Has     D. Were
19. Without air, we _____ forced to seek shelter from the sun, as there _____ no atmosphere to protect us from the sun’s deadly rays.
A. will be, will be            B. may be, may be    C. would be, would be  D. are, is
20. In the absence of friction, belts _____ in conveying power from one machine to another.
A. will not be used                B. may not be used
C. can not be used                D. could not be used