英語中的虛擬語氣是四、六級考試的必考考點。如果你掌握了以下十八個例句，再做好文後所配的練習，虛擬語氣難題就可以迎刃而解了。
一、虛擬語氣在條件從句中的用法
(一)形式
略
註：
1.在從句中，be動詞多用were的形式。在口語中，如果主語是第一、第三人稱單數的話，be動詞可用was，但人們總是說：If I were you...
2.主句中的謂語可以由would，should，could和 might這四個不同的情態動詞來構成。
3.與將來事實相反的條件從句中，謂語有三種不同的形式：過去式、were +to do或should +do。
例句1：If I were you，I would study hard.我要是你的話，我就會好好學習。(與現在事實相反)
例句2：If I had studied hard，I would have passed CET-6 last semester.我要是早就好好學習的話，那麼我上個學期就通過六級考試了。(與過去事實相反)
例句3：If Iwere to pass CET-6，I would treat you to dinner at KFC.我要是過了六級考試，就請你去吃肯德基。(與將來事實相反)
(二)省略/倒裝
如果在虛擬從句中包含有一個助動詞、情態動詞、動詞be或have，則可把if省略，把上類動詞提到主語之前，使用倒裝語序。
例句4：Had it not been for the PLA，we wouldn't have been able to beat the flood.4要不是人民解放軍，我們是無法戰勝洪水的。
例句5：Were he here now，he would certainly help me.5他要是在這裡肯定會幫我的忙。
注4：例句4中的從句部分出現了否定詞not，如果把該句還原成正常語序，應該是：
If it hadn't been for the PLA，we wouldn't have been able to beat the flood.
但是一旦句子發生了省略，就必須把hadn't分開，否定詞not還原，放在主語之後，不可寫成Hadn't it been for的形式。
注5：在虛擬條件從句中，動詞be在正常語序中常用were，在口語中，當主語是第一、第三人稱單數時，可用was，但在if的倒裝句中，必須用were。
(三)錯綜時間條件句
有時，從句和主句中所表示的動作發生的時間是不一致的，這時就要根據其所表示的時間來進行調整。
例句6：If I were you，I would have gone to see the doctor.我要是你，我早就去看病了。(從句與現在事實相反，主句與過去事實相反)
例句7：If you had gone to see the doctor，you would be all right now.你要早去看病，你現在就沒事了。(從句與過去事實相反，主句與現在事實相反)
(四)含蓄條件句
虛擬的條件有時可以不用條件從句來表示，而是通過某些介詞短語來表達。
例句8：But for the English test，I would have gone home this week.6要不是英語測試，我這個禮拜就回家了。
注6：除了but for(要不是)以外，能夠表示虛擬條件的詞和短語還包括：but that(要不是)、without(沒有)、otherwise(否則)、or(不然)、under...circumstances(在……的情況下)、in the past(在過去)等等。
過級考試真題
1.He must have had an accident，or he then.
A.would have been here B.had to be here
C.should be here D.would be here
2.It was essential that the application forms back before the deadline.
A.must be sent B.would be sent C.be sent D.were sent
3.We desire that the tour leader us immediately of any change in plans.
A.inform B.informs C.informed D.has informed
4.Look at the terrible situation I am in!If only I your advice.
A.follow B.had followed C.would follow D.have followed
5.It is recommended that the project until all the preparations have been made.
A.is not started B.will not be started
C.not be started D.is not to be started
6.I wish I longer this morning，but I had to get up and come to class.
A.could have slept B.slept C.might have slept D.have slept
7.We didn't know his telephone number;otherwise we him.
A.would have telephoned B.must have telephoned C.would telephone D.had telephoned
8.The story written by the famous writer is as real as if it only yesterday.
A.happened B.had happened C.was happening D.happen
9.It is necessary that a good engineer a basic training in general science.
A.be given B.is given C.will be given D.was given
10.I suggested that the students each a plan for the summer vacation.
A.would make B.make C.will make D.made
11.She said she'd rather he tomorrow instead of today.
A.comes B.will come C.had come D.came
12.I'd lend you my bicycle I could remember who last used it.
A.except that B.if only C.on condition that D.considering that
13.It is politely requested by the hotel management that radios after 11o'clock.
A.were not played B.not to play C.not be played D.did not play
14.Jean doesn't want to work right away because she thinks that if she a job she probably wouldn't be able to see her friends very often.
A.has to get B.were to get C.had got D.could have got
15. before we depart the day after tomorrow，we should have a wonderful dinner party.
A.Had they arrived B.Would they arrive C.Were they arriving D.Were they to arrive
16.It is important that enough money to fund the project.
A.be collected B.must be collected C.was collected D.can be collected
17.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
18.Had he worked harder，he the exams.
A.must have got through B.would have got through
C.would get through D.could get through
19.I don't think it advisable that Tom to the job since he has no experience.
A.is assigned B.will be assigned
C.be assigned D.has been assigned
二、虛擬語氣在其他從句中的用法
(一)賓語從句
1.wish後的賓語從句
例句9：I wish I were as young as you.7我希望自己像你一樣年輕。
注7：wish從句後使用虛擬語氣時，動詞的形式根據所表示的時間概念而採用不同形式：過去時(與現在相反)、過去完成時(與過去事實相反)或過去將來時(與將來事實相反)。
2.would rather和would sooner後的賓語從句
兩個詞組都表示寧願、寧可的意思，後面如用賓語從句，動詞採用過去時(與現在或將來事實相反)或過去完成時(與過去事實相反)。
例句10：I'd rather I hadn't met you.8我寧願從來就沒遇見過你。
注8：would rather和would sooner兩詞組除了要掌握它們後面賓語從句中虛擬語氣的用法以外，還要知道這兩個詞組後面都可以直接加動詞原形，這也是四、六級考試中的一大考點，如：美國歌曲《山鷹》中的第一句歌詞就是：I'd rather be asparrow than a snail.其中，就使用了句式would rather do than do(寧願做……而不做……)。
3.suggest等動詞後的賓語從句
表示主觀判斷、推測、建議、命令和要求的動詞通常引起虛擬的賓語從句，此類動詞後的賓語從句中採用should +do、should可以省略的虛擬語氣形式。該類動詞包括：
(1)高中詞彙：advise(勸告)、ask(要求)、decide(決定)、insist(堅持)、order(下令)、suggest(建議)等。
(2)四、六級常考詞彙：command(命令)、demand(要求)、desire(渴望)、propose(提議)、recommend(勸告)、require(要求)等。
(3)其他詞彙：consent(同意)、deserve(值得提
起)、maintain(主張)、move(提議)、urge(極力主張)、 vote(提議)等。
例句11：I recommend that you all be diligent if you want to pass the exam.如果你們要考及格，我勸你們勤奮學習。
(二)主語從句
在It is +形容詞/某些動詞的過去分詞+主語從句的結構中，從句的謂語動詞須用動詞原形或 should +do的形式。這些形容詞包括：
(1)高中詞彙：decided(決定的)、important(重要的)、ordered(命令的)等。
(2)四、六級常考詞彙：advisable(合理的)、demanded(要求的)、desired(期望的)、desirable(合乎需要的)、essential(緊要的)、insistent(堅持的)、natural(自然的)、preferable(更可取的)、proposed(建議的)、 recommended(推薦的)、required(要求的)、urgent(緊迫的)、vital(極其重要的)等。
(3)其他詞彙：appropriate(適當的)、arranged(安排好的)、better(較好的)、imperative(迫切的)、possible(可能的)、probable(可能的)、resolved(決心的)、 strange(奇怪的)、suggested(建議的)等。
例句12：It is highly desirable that a new mayor be appointed for this city.這座城市急需任命一位新市長。
(三)表語從句和同位語從句
有些名詞引起的表語從句或同位語從句中，謂語動詞須用動詞原形或should +do的形式。這些名詞包括：advice(忠告)、decision(決定)、demand(要求)、desire(渴望)、idea(想法)、motion(提議)、necessity(必要性)、order(命令)、plan(計劃)、preference(偏愛)、proposal(建議)、recommendation(推薦)、requirement(要求)、suggestion(建議)等。
例句13：His proposal is that we turn off TVfor half an hour every day.他建議我們每天少看半個小時的電視。
特別提示：從以上的各類從句中我們可以得到以下的推論，即當一個動詞後面的賓語從句中要使用(should)+do的虛擬語氣形式時，則可推理出用法相同的一組從句。以動詞advise為例：
(1)I advise that we stay and wait here.(動詞後的賓語從句)
(2)It is advised that we stay here.(It is +動詞的過去分詞+that引導的主語從句)
(3)It is advisable that we stay here.(It is +由該動詞轉換的形容詞+that引導的主語從句)
(4)My advice is that we stay here.(由該動詞轉換的名詞後的表語從句)
(5)I offered the advice that we stay here.(由該動詞轉換的名詞後的同位語從句)
(6)I think it advisable that we stay here.(由該動詞轉換的形容詞作賓語補足語，it為形式賓語，真正的賓語從句中使用虛擬語氣)
以上六類從句中所使用的都為(should)+do的虛擬語氣形式。
歷年MBA考題
20.If you had rung up the TV repairman，you the sports program.
A.could watch B.could be watching
C.could have watched D.could not watch
21.If you had taken your umbrella with you when you went to work this morning，you wet now.
A.will not be B.will not have been
C.would not be D.would not have been
22.If this university such a good reputation，I would not have come here.
A.didn't have B.doesn't have
C.would not be D.would not have been
23.She did not go to the North，instead she remained here in the South.The doctor suggested that she there.
A.not go B.go not C.couldn't go D.didn't go
24. ，call the police.
A.If anyone will attempt to break in
B.Would anyone attempt to break in
C.Anyone should attempt to break in
D.Should anyone attempt to break in
(四)狀語從句
1.as if/as though引導的狀語從句
as if/as though(仿佛、好像)引起方式狀語從句，從句中的虛擬語氣形式與wish後的賓語從句相同：
a.一般過去時(表示與現在事實相反)
b.過去完成時(表示與過去事實相反)
c.would +do(表示與將來事實相反)
例句14：You look as if you had seen a ghost.你看起來好像撞見鬼了。
2.lest/in case /for fear that引導的狀語從句
lest(以防、以免)、in case(萬一、以防)、for fear that(因恐、免得)引起的狀語從句中，謂語動詞要使用(should)+do的形式。
例句15：The old woman walked slowly lest she(should)slip.老太太走得很慢，以免滑倒。
3.whoever等引導的狀語從句
由連接代詞whoever(無論誰)、whatever(無論什麼)、whichever(無論哪個)等和連接副詞however(無論如何)、whenever(無論何時)、wherever(無論哪裡)等及 no matter+how/what/when /where /who(無論怎樣/什麼/何時/哪裡/誰)構成的詞組引導的讓步狀語從句，若表示說話人對現在或將來的推測，謂語動詞常用虛擬語氣，形式為動詞原形或may /might+do。
例句16：Whichever be the case，my situation remained the same.無論是哪種情況，我的處境都一樣。
(五)定語從句
It is time(是……時候了)，Itis about time(差不多是……時候了)，It is high time that(該……了)句式中，that引導的定語從句中用過去時表示虛擬。
例句17：It is time that we protected our environment.我們應該保護我們的環境了。
三、虛擬語氣在表示祝願的句子中的應用
在if only或if...only(但願、要是……就好了)引起的表示遺憾的感嘆句中，謂語動詞使用虛擬語氣，形式為過去時。
例句18：If only I could see Jordan.我要是能見到喬丹就好了。
以上的十八句是筆者精心設計的，每一個句子都是虛擬語氣的一個考點，如果能夠把這十八句融會貫通，達到舉一反三的程度，虛擬語氣部分則可輕鬆過關。
歷年考研試題
25.There is a real possibility that these animals could be frightened， a sudden loud noise.