條件是否能夠?qū)崿F(xiàn)，能夠?qū)崿F(xiàn)是真實(shí)條件句，不能使用虛擬語氣；假設(shè)的條件不能實(shí)現(xiàn)則是非真實(shí)條件句，要用虛擬語氣。
判斷這個(gè)假設(shè)是與哪個(gè)事實(shí)相反。通常有三種情況：①與過去事實(shí)相反。②與現(xiàn)在事實(shí)相反。③與將來事實(shí)可能相反。
3、“后退一步法”
后退一步法是指在準(zhǔn)確地判斷了該句與哪一事實(shí)相反后，按虛擬語氣的后退一步法處理從句謂語動(dòng)詞的時(shí)態(tài)。即：在非真實(shí)條件狀語從句中，謂語動(dòng)詞按正常情況“后退一步”。也就是：
①與過去事實(shí)相反，在從句中用過去完成時(shí)形式表示。
②與現(xiàn)在事實(shí)相反，在從句中用過去一般時(shí)形式表示。
③與將來事實(shí)可能相反，在從句中用過去將來時(shí)形式表示。
主句中則用情態(tài)動(dòng)詞would，should，could 等加一個(gè)與從句一致的動(dòng)詞形式。例：
⑴、If I had come her yesterday，I would have seen him.
⑵、If I were a teacher，I would be strict with my students.
⑶、If it should snow tomorrow，they couldn't go out.
4、注意事項(xiàng)
①if條件句中如有were，should，had，可以省去if，并使用倒裝語序。
②在現(xiàn)代英語中if條件狀與從句中的謂語動(dòng)詞如果是be其過去形式一般用were.
二、虛擬語氣在if 引導(dǎo)的條件句中的用法：
（一）、表示與現(xiàn)在事實(shí)相反的情況。其句子結(jié)構(gòu)為：
從句：if + 主語+ 動(dòng)詞的過去式（be 用were） + ……
主句：主語+ would （should，could ，might） + 動(dòng)詞原形+ ……
例：
1.If I were you，I would go with him.
2.If the weather were fine，I would go there.
如果天氣好，我去那兒。（事實(shí)天氣不好）
3.If I were you，I would read it again.
如果我是你的話，我再讀一遍。（事實(shí)上我不是你）
4.If time permitted，I would write it again.
如果時(shí)間允許的話，我再寫一遍。（事實(shí)上時(shí)間不允許）
5.If it weren‘t snowing，we wouldn’t stay in the house.
要是現(xiàn)在不下雪的話，我們就不會(huì)待在屋里。（事實(shí)上現(xiàn)在下雪）
6.What would I do if I were in your place？
要是我處于你地位我會(huì)怎么辦？（事實(shí)上我不在你的位置上）
7.If he hurried，he could catch the first bus.
他要是快點(diǎn)能夠趕上頭班公共汽車。（可是他不著急）
8.If it weren‘t for your help，we would get into trouble.
如果沒有你們的幫助，我們就會(huì)陷入困境。（而事實(shí)上得到了你們的幫助）
9.If we had the manpower， we could open up even more land.
如果有人力，我們還能開更多的荒地。
10. If I were you，I would go with him.
（從句If I were you，主句I would go with him.）
11. If I were you，I should buy it.
（從句用過去式動(dòng)詞were，主句用動(dòng)詞原形buy）
12. If I had time，I would study French.
（如果有時(shí)間，我會(huì)學(xué)習(xí)法文。）（從句用過去式動(dòng)詞had，主句用動(dòng)詞原形study）
13. If she knew English，she would not ask me for help.
（如果她懂英文，她就不必要我?guī)土?。）（從句用過去式動(dòng)詞knew，主句用動(dòng)詞原形ask）
注意：如果動(dòng)作在進(jìn)行中，主句要用："主語+ would be + 進(jìn)行式動(dòng)詞+ ……"
14. If they were here，he would be speaking to them now.
（從句用過去式動(dòng)詞were，主句用would be speaking）
（二）、表示與過去事實(shí)相反的虛擬條件句。其句子結(jié)構(gòu)為：
從句：If + 主語+ had +過去完成式動(dòng)詞+ ……
主句：主語+ would （should，could，might） + have +過去完成式動(dòng)詞+……
例如：
⑴、If you had taken my advice，you would not have made such a mistake.如果你聽了我的勸告，就不會(huì)犯這樣的錯(cuò)誤。（事實(shí)上你沒有聽我的勸告）
⑵、I shouldn‘t have been able to write such good novels if I hadn’t lived among the peasants for five years.如果我不是和農(nóng)民生活了五年，就不可能寫出這樣好的小說。（事實(shí)上我和農(nóng)民生活了五年）
⑶、If you hadn‘t invited me，I shouldn’t have come to the party.如果你不邀請我，我就不會(huì)來參加你的舞會(huì)。（事實(shí)上你邀請了我）
⑷、If it hadn‘t been for your help，I shouldn’t have finished this work on time. 要是沒有你們的幫忙，我就不會(huì)按時(shí)完成了這項(xiàng)工作。（事實(shí)上你們幫助了我）
⑸、If he hadn‘t broken the law，he wouldn’t have been put in prison.如果他不違法的話，就不會(huì)被打入監(jiān)獄。（事實(shí)上他違法了）
⑹、If I hadn‘t been ill yesterday，I might have come to school.昨天要是不生病，我是可能來上學(xué)的。（事實(shí)上我生病了）
⑺、If I had been your headmaster，I should have dismissed you from school. 我要是你們校長的話，就把你開除學(xué)籍了。（事實(shí)上我不是）
⑻、If you had studied harder last term，you could have passed exam.（從句動(dòng)詞用had studied，主句動(dòng)詞用have passed）如果你在上個(gè)學(xué)期用功一些，你就會(huì)在考試中過關(guān)了。
⑼、If you had taken my advice，you wouldn't have failed in the exam.（從句動(dòng)詞用had taken，主句動(dòng)詞用have failed）如果你當(dāng)時(shí)聽從我的勸告的話，你就不會(huì)在考試中失敗了。
⑽、If you had got up earlier，you could have caught the train.（從句動(dòng)詞用had got up，主句動(dòng)詞用have caught）如果你起身得早一點(diǎn)，你就會(huì)趕得上火車了。
⑾、If it had snowed，I would have skied in the park.（從句動(dòng)詞用had snowed， 主句動(dòng)詞用have skied）如果下雪的話，我就可在公園里滑雪了。
注意：如果動(dòng)作在進(jìn)行中，主句要用："主語+ would + have + 完成進(jìn)行式動(dòng)詞 +……
⑿、If they had been here，he would have been speaking to them.（從句動(dòng)詞用had been， 主句動(dòng)詞用have been speaking）
（三）、表示與將來事實(shí)相反的虛擬條件句（對將來的事實(shí)實(shí)現(xiàn)的可能性不大）。其句子結(jié)構(gòu)為：
從句：If + 主語+ should （或were） + 動(dòng)詞原形+……
主句：主語+ would （could，should，might） + 動(dòng)詞原形+……
例如：
⑴、If I were to work at this problem，I would do it in another way.要是我來解這道難題，我會(huì)用另外一種方法的。
⑵、If you were to do such a thing again，you would be punished. 如果你再做這樣的事情，就會(huì)受到懲罰。
⑶、If I should work harder，I could make much more progress.假如我更努力學(xué)習(xí)的話，我會(huì)取得更大的進(jìn)步。（事實(shí)上我不可能努力學(xué)習(xí)）
⑷、If it should rain tomorrow，I would stay at home.如果明天下雨的話，我將待在家里。（根據(jù)天氣情況，明天不可能下雨）
⑸、If he should come，I could ask him for some advice.萬一他來了，我就能夠向他請教。（事實(shí)上他來的可能性很?。?BR> ⑹、If he came tomorrow，I would do it with him.如果明天他來的話，我將和他一起做此事。（事實(shí)上他來的可能性很小）
⑺、 If it should rain，the crops would be saved.（從句動(dòng)詞用should rain，主句動(dòng)詞用be）如果天下雨，莊稼可能就收獲了。
⑻、 If he were to go fomorrow，he might tell you.（從句動(dòng)詞用were to，主句動(dòng)詞用tell）如果明天他走的話，他可能會(huì)告訴你。
⑼、 If he were here，I would give him the books.（從句動(dòng)詞用were，主句動(dòng)詞用give）如果他在這兒，我可能會(huì)把書給他。
注意：如果動(dòng)作在進(jìn)行中，從句（不是主句喔）要用："If + 主語+ 過去進(jìn)行式動(dòng)詞 +……"
⑽、 If she were staying here now，I would let her ride my horse.（從句動(dòng)詞用were staying， 主句動(dòng)詞用let）如果她現(xiàn)在留在這兒，我可能會(huì)讓她騎我的馬。
三、混合條件句——主從句時(shí)間不一致情況下的虛擬語氣
有時(shí)條件從句中的動(dòng)作和結(jié)果與主句中的動(dòng)作，發(fā)生的時(shí)間不一致，這時(shí)動(dòng)作的形式應(yīng)根據(jù)它所表示的時(shí)間加以調(diào)整。如：
1. 從句表示過去，主句表示將來：
⑴、If they had started the early morning yesterday，they would be here now.
⑵、If we hadn' t made adequate preparations，we shouldn' t dare to do the experiment next week.
2. 從句表示將來，主句表示過去：
⑴、If I were not to make a preparation for my experiment this afternoon，Iwould have gone to see the film with you last night.
3.從句表示過去，主句表示將來：
⑴、If we hadn't made adequate preparations，we shouldn't dare to do theexperiment next week.
4.從句表示將來，主句表示現(xiàn)在：
⑴、If we shouldn't have an exam this afternoon，I would go shopping now.
5.從句表示過去，主句表示現(xiàn)在。
⑴、If they had stared the early morning yesterday，they would be here now.
⑵、If you had followed my advice，you would be able to finish the work now.
如果你當(dāng)時(shí)聽了我的話，現(xiàn)在就能完成這份工作了。（從句說明過去，主句說明現(xiàn)在。）
6.從句表示現(xiàn)在，主句表示過去
⑴、If I were you，I would have gone to her birthday party.如果我是你，我就去參加她的生日晚會(huì)了。（從句說明現(xiàn)在，主句說明過去。）
7.從句表示過去，主句表示過去和現(xiàn)在
⑴、If you hadn‘t lent me some money，I couldn’t have bought the new house and most likely I would be still living in the dangerous house now.
假若你不借錢給我，我不可能買下這幢新房，很可能現(xiàn)在還住在危房里。（從句說明過去，主句說明過去和現(xiàn)在。）
四、含蓄條件句
非真實(shí)條件句中的條件從句有時(shí)不表出來，只暗含在上下文中，這種句子叫做含蓄條件句。含蓄條件句大體有三種情況；
1. 條件暗含在短語中。如：
（1）、What would I have done without you？如沒有你，我會(huì)怎么辦呢？（條件暗含在分詞短語without you中）
（2）、It would be easier to do it this way. 這樣做會(huì)比較容易。（條件暗含在不定式短語to do it this way中）
（3）、This same thing， happening in wartime，would lead to a disaster. 同樣的事，如發(fā)生在戰(zhàn)時(shí)，就會(huì)釀成大禍。（條件暗含在分詞短語happening in wartime中）
（4）、But for your help we couldn‘t have succeeded in the experiment. 如果沒有你的幫助，我們的實(shí)驗(yàn)是不會(huì)成功。（暗含條件是but for your help）
（5）、He must have the strength of a hippopotamus，or he never could have vanquished that great beast. 他一定是力大如河馬，否則他絕不會(huì)擊敗那只龐大的野獸。（暗含條件是連詞or）
（6）、Alone，he would have been terrified. 如是單獨(dú)一人，他是會(huì)感到害怕的。（暗含條件是alone）
2. 條件暗含在上下文中。如：
（7）、You might stay her forever. 你可以永遠(yuǎn)待在這兒。（可能暗含if you wanted to）
（8）、We would have succeeded. 我們本來是會(huì)成功的。（可能暗含if we had kept trying）
（9）、Your reputation would be ruined. 你的名譽(yù)會(huì)敗壞的。（可能暗含if you should accept it）
（10）、I would appreciate a little of your time. 謝謝你給我一點(diǎn)時(shí)間吧。（可能暗含if you were so kind as to give me a little of your time）
3. 在不少情況下，虛擬式已變成習(xí)慣說法，很難找出其暗含的條件。如：
（11） 、You wouldn‘t know. 你不會(huì)知道。
（12） 、I would like to come. 我愿意來。
（13） 、I wouldn‘t have dreamed of it. 這是我做夢也不會(huì)想到的。
（14） 、He told the story in such minute detail that he might himself have been an eye-witness. 他將那事講的非常仔細(xì)，簡直就象他親眼看見一樣。
五、條件從句中省略if 采用倒裝語序的情況
1、在if引導(dǎo)的表示虛擬的條件狀語從句中，有時(shí)可以把含有助動(dòng)詞、情態(tài)動(dòng)詞、be或have的虛擬條件句中的連詞if 省去，而將had ，should，were 等詞提到主語之前，即用倒裝結(jié)構(gòu)。
例如：
1）、原句：If she were younger， she would do it.
去If：Were she younger，she would do it. （把動(dòng)詞were移到主語she的前面）
2）、原句：If he had tried it，he could have done it.
去If：Had he tried it，he could have done it.（把had移到主語he的前面）
3）、Had he worked harder，he would have got through the exams.
4）、Were he to leave today，he would get there by Friday.
5）、Were I in your place，I wouldn‘t do that.
6）、Had I seen the film，I would have discussed it with them last night.
假如我看了那部電影，昨晚我就可以和他們一起討論了。
7）、Were I a bird，I could fly freely.
假如我是一只小鳥，我就能自由翱翔。
8）、Should it rain next week the farmers would have a good harvest.
要是下周能下雨的話，農(nóng)民們就能有個(gè)好收成了。
2、如果虛擬條件句中有were，had或should時(shí)，把它們放在if的位置上；但是如果條件句中沒有were，had或should不能用倒裝。例如：
⑴、Should it rain tomorrow，what should we do？要是明天下雨的話，我們怎么辦呢？
⑵、Were I you， I would have asked him for some advice.要是我是你的話，我就向他請教了。
⑶、Were he to do this work by himself，he would get a lot of money.如果他自己能夠做此工作，他就會(huì)得到一些錢。
3、在“開放式條件句”（open conditional clause）和讓步狀語從句中should是被省略了的。在這種情況下，如果if省略，動(dòng)詞be與主語的位置要倒裝。如：
⑴、If any person be guilty of a crime，the court shall have the right to appeal. （任何人犯罪，法院有權(quán)起訴。）
Be any person guilty of a crime，the court shall have the right to appeal.
⑵、Whether she be right or wrong，she will have my unanswering support. （不管她是對還是錯(cuò)，我都會(huì)支持她的。）
Be she right or wrong，she will have my unanswering support.
⑶、____ ，I will take her as my wife.
［A］Were she rich or poor
［B］Being rich or poor
［C］Be she poor or rich
［D］Whether is she poor or rich
4、注意：有時(shí)虛擬條件句并沒來if 從句表示出來，而是用介詞短語（otherwise，or，without，but for）、上下文或其它方式來表示。
⑴、We didn't know his telephone number；otherwise we would have telephoned him.
⑵、Without you help，I wouldn‘t have achieved so much.
⑶、But for your help，I would not have succeeded.
六、有時(shí)虛擬條件句的從句或主句都可以省略其中一個(gè)：
1. I could help you. （只有主句）
2. If I had time. （只有從句）
3. She should have come to the meeting. （只有主句）
4. If he had much more money. （只有從句）
第二節(jié)：其他形式的條件句中的虛擬語氣
一、用“without/but for/in the absence of ”表示“要不是”，“如果沒有”（相當(dāng)于if it were not for…）表示條件時(shí)，句中一般用虛擬語氣。（也可用陳述語氣）
Without your help，I couldn' t finish my work on time.
In the absence of water and air，nothing could live.
二、由“providing （that）/ provided （that）/on condition that/ in order that“引導(dǎo)的條件從句或目的從句，根據(jù)情況，可用虛擬語氣。（有時(shí)也可用陳述語氣）
They are willing surrender provided they are given free passage.
三、用without / but for / in the absence of 表示"要不是"、"如果沒有"，表示條件虛擬句：
（1）、Without air，nothing could live.要是沒有空氣，什么也不能生存。
（2）、But for your assistance，we could not accomplish it.要不是你的幫忙，我們是難有成就的。
（3）、In the absence of water and air，nothing could live.如果沒有水和空氣，什么也不能生存。
第五部分：其他幾種情況下的虛擬語氣
第一節(jié)：虛擬語氣在as if / as though 引導(dǎo)的方式狀語從句中的應(yīng)用
虛擬語氣在as if / as though 引導(dǎo)的方式狀語從句中，謂語動(dòng)詞形式與wish后的賓語從句基本相同
1.表示與現(xiàn)在事實(shí)相反或?qū)ΜF(xiàn)在情況有懷疑，謂語動(dòng)詞用過去式。例如：
（1）、.He felt as if he alone were responsible for what had happened.他感到仿佛唯獨(dú)他要對發(fā)生的一切負(fù)責(zé)。
（2）、He acts as if he were / was a TV expert.他做起事來好象是個(gè)電視專家。
（3）、Alan talked about Rome as if he were a Roman.艾倫談起羅馬來好像他是個(gè)羅馬人一樣。
（4）、John pretends as if he didn' t know the thing at all，but in fact he knows it very well.（用過去式表示與現(xiàn)在事實(shí)相反的假設(shè)）
（5）、He pretends as if he didn't know the thing at all，but in fact he knows it very well.（用過去式表示與現(xiàn)在事實(shí)相反的假設(shè)）他假裝好象完全不懂那事，其實(shí)他對那事非常了解。
2. 表示過去想象中的動(dòng)作或情況，謂語動(dòng)詞用過去完成式。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
那棵樹看上去好象很久沒人給澆水了。（答案是c）
（2）、The old man looked at the picture，he felt as though he had gone back to time 20 years ago.（用過去完成式表示與過去相反的事實(shí)）
（3）、The old man looked at the picture，he felt as though he had gone back to time 20 years ago.（用過去完成式表示與過去相反的事實(shí)）那老人看著照片，他覺得仿佛回到20年前的時(shí)光。
3.表示與將來事實(shí)相反：
（1）、They talked and talked as if they would never meet again （would+動(dòng)詞原形，表示與將來事實(shí)相反）
（2）、They talked and talked as if they would never meet again.（would + 原形動(dòng)詞meet，表示與將來事實(shí)相反）他們談了又談，仿佛他們不會(huì)再相見的樣子。
注：在as if / as though 句中，如果有可能成為事實(shí)，用陳述語氣。
He looks as if he is going to be ill.
第二節(jié)：虛擬語氣用在lest，for fear that及in case引導(dǎo)的目的狀語從句中
在由lest等引導(dǎo)的目的狀語從句中需用虛擬語氣，表示“以防，以免”等意思，其謂語動(dòng)詞多由should ＋動(dòng)詞原形構(gòu)成，should也可省略。
例如：
⑴、He was punished lest he should make the same mistake again.他被處以懲罰以免他再犯。
⑵、The mad man was put in the soft-padded cell lest he _____ himself.
a. injure b. injured c. had injure d. would injure
這個(gè)瘋子被關(guān)進(jìn)墻上裝有襯墊的病房，以免傷了他自己。（答案是a）
第三節(jié)：介詞短語表示虛擬
有時(shí)假設(shè)的情況并不以條件從句表示出來，而是通過一個(gè)介詞短語來表示，或通過上下文或其他方式表示出來。如but for，but that…，in case of，otherwise，supposing，under more favourable condition，without 等表示讓步假設(shè)。
1）、He worked very hard； otherwise he might have failed. （他刻苦工作，不然他就失敗了。）
2）、We could have done better under more favorable conditions.（假設(shè)我們有更有利條件，我們還會(huì)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
第四節(jié)：虛擬語氣用在It is（about ／high）time ＋that定語從句中
在It is（about／high）time ＋that定語從句中需用虛擬語氣，表示“該做……的時(shí)候了”，其動(dòng)詞形式用一般過去時(shí)或should ＋動(dòng)詞原形。
（1）、It's already 5 o'clock now.Don't you think it's about time we went home？現(xiàn)在已經(jīng)5點(diǎn)鐘了，你不認(rèn)為我們應(yīng)該回家了嗎？
（2）、It is about time you were in bed.
（3）、It is high time we left.
（4）、It is the first time I came here.
注：
1、在this is the first time ／second time that.……句型中，從句中謂語動(dòng)詞用陳述語氣完成時(shí)態(tài)。
例如：
Is this the first time that you have visited Hongkong？這是你第一次參觀香港嗎？
2、It's time to do something有別于It's time that.……
第五節(jié)：在if only 引起的感嘆句中需用虛擬語氣
謂語動(dòng)詞用過去式或過去完成式（謂語動(dòng)詞與wish賓語從句的虛擬形式相同）。
⑴、If only he didn‘t drive so fast?。ìF(xiàn)在）
⑵、If only she had asked someone‘s advice.（過去）
⑶、If only the rain would stop.（將來）
例題解析：
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 引出感嘆句，意思是“要是……多好”，表示說話人的一種愿望，希望發(fā)生（事實(shí)上不可能發(fā)生）與過去事實(shí)相反的情況。本句的全句意思是：“看我現(xiàn)在的處境多糟糕！要是我聽從你的勸告多好”。事實(shí)上，句中的“我”沒有聽從勸告，所以處境很糟糕。
題中空格處應(yīng)當(dāng)用虛擬語氣，答案是B.
判斷這個(gè)假設(shè)是與哪個(gè)事實(shí)相反。通常有三種情況：①與過去事實(shí)相反。②與現(xiàn)在事實(shí)相反。③與將來事實(shí)可能相反。
3、“后退一步法”
后退一步法是指在準(zhǔn)確地判斷了該句與哪一事實(shí)相反后，按虛擬語氣的后退一步法處理從句謂語動(dòng)詞的時(shí)態(tài)。即：在非真實(shí)條件狀語從句中，謂語動(dòng)詞按正常情況“后退一步”。也就是：
①與過去事實(shí)相反，在從句中用過去完成時(shí)形式表示。
②與現(xiàn)在事實(shí)相反，在從句中用過去一般時(shí)形式表示。
③與將來事實(shí)可能相反，在從句中用過去將來時(shí)形式表示。
主句中則用情態(tài)動(dòng)詞would，should，could 等加一個(gè)與從句一致的動(dòng)詞形式。例：
⑴、If I had come her yesterday，I would have seen him.
⑵、If I were a teacher，I would be strict with my students.
⑶、If it should snow tomorrow，they couldn't go out.
4、注意事項(xiàng)
①if條件句中如有were，should，had，可以省去if，并使用倒裝語序。
②在現(xiàn)代英語中if條件狀與從句中的謂語動(dòng)詞如果是be其過去形式一般用were.
二、虛擬語氣在if 引導(dǎo)的條件句中的用法：
（一）、表示與現(xiàn)在事實(shí)相反的情況。其句子結(jié)構(gòu)為：
從句：if + 主語+ 動(dòng)詞的過去式（be 用were） + ……
主句：主語+ would （should，could ，might） + 動(dòng)詞原形+ ……
例：
1.If I were you，I would go with him.
2.If the weather were fine，I would go there.
如果天氣好，我去那兒。（事實(shí)天氣不好）
3.If I were you，I would read it again.
如果我是你的話，我再讀一遍。（事實(shí)上我不是你）
4.If time permitted，I would write it again.
如果時(shí)間允許的話，我再寫一遍。（事實(shí)上時(shí)間不允許）
5.If it weren‘t snowing，we wouldn’t stay in the house.
要是現(xiàn)在不下雪的話，我們就不會(huì)待在屋里。（事實(shí)上現(xiàn)在下雪）
6.What would I do if I were in your place？
要是我處于你地位我會(huì)怎么辦？（事實(shí)上我不在你的位置上）
7.If he hurried，he could catch the first bus.
他要是快點(diǎn)能夠趕上頭班公共汽車。（可是他不著急）
8.If it weren‘t for your help，we would get into trouble.
如果沒有你們的幫助，我們就會(huì)陷入困境。（而事實(shí)上得到了你們的幫助）
9.If we had the manpower， we could open up even more land.
如果有人力，我們還能開更多的荒地。
10. If I were you，I would go with him.
（從句If I were you，主句I would go with him.）
11. If I were you，I should buy it.
（從句用過去式動(dòng)詞were，主句用動(dòng)詞原形buy）
12. If I had time，I would study French.
（如果有時(shí)間，我會(huì)學(xué)習(xí)法文。）（從句用過去式動(dòng)詞had，主句用動(dòng)詞原形study）
13. If she knew English，she would not ask me for help.
（如果她懂英文，她就不必要我?guī)土?。）（從句用過去式動(dòng)詞knew，主句用動(dòng)詞原形ask）
注意：如果動(dòng)作在進(jìn)行中，主句要用："主語+ would be + 進(jìn)行式動(dòng)詞+ ……"
14. If they were here，he would be speaking to them now.
（從句用過去式動(dòng)詞were，主句用would be speaking）
（二）、表示與過去事實(shí)相反的虛擬條件句。其句子結(jié)構(gòu)為：
從句：If + 主語+ had +過去完成式動(dòng)詞+ ……
主句：主語+ would （should，could，might） + have +過去完成式動(dòng)詞+……
例如：
⑴、If you had taken my advice，you would not have made such a mistake.如果你聽了我的勸告，就不會(huì)犯這樣的錯(cuò)誤。（事實(shí)上你沒有聽我的勸告）
⑵、I shouldn‘t have been able to write such good novels if I hadn’t lived among the peasants for five years.如果我不是和農(nóng)民生活了五年，就不可能寫出這樣好的小說。（事實(shí)上我和農(nóng)民生活了五年）
⑶、If you hadn‘t invited me，I shouldn’t have come to the party.如果你不邀請我，我就不會(huì)來參加你的舞會(huì)。（事實(shí)上你邀請了我）
⑷、If it hadn‘t been for your help，I shouldn’t have finished this work on time. 要是沒有你們的幫忙，我就不會(huì)按時(shí)完成了這項(xiàng)工作。（事實(shí)上你們幫助了我）
⑸、If he hadn‘t broken the law，he wouldn’t have been put in prison.如果他不違法的話，就不會(huì)被打入監(jiān)獄。（事實(shí)上他違法了）
⑹、If I hadn‘t been ill yesterday，I might have come to school.昨天要是不生病，我是可能來上學(xué)的。（事實(shí)上我生病了）
⑺、If I had been your headmaster，I should have dismissed you from school. 我要是你們校長的話，就把你開除學(xué)籍了。（事實(shí)上我不是）
⑻、If you had studied harder last term，you could have passed exam.（從句動(dòng)詞用had studied，主句動(dòng)詞用have passed）如果你在上個(gè)學(xué)期用功一些，你就會(huì)在考試中過關(guān)了。
⑼、If you had taken my advice，you wouldn't have failed in the exam.（從句動(dòng)詞用had taken，主句動(dòng)詞用have failed）如果你當(dāng)時(shí)聽從我的勸告的話，你就不會(huì)在考試中失敗了。
⑽、If you had got up earlier，you could have caught the train.（從句動(dòng)詞用had got up，主句動(dòng)詞用have caught）如果你起身得早一點(diǎn)，你就會(huì)趕得上火車了。
⑾、If it had snowed，I would have skied in the park.（從句動(dòng)詞用had snowed， 主句動(dòng)詞用have skied）如果下雪的話，我就可在公園里滑雪了。
注意：如果動(dòng)作在進(jìn)行中，主句要用："主語+ would + have + 完成進(jìn)行式動(dòng)詞 +……
⑿、If they had been here，he would have been speaking to them.（從句動(dòng)詞用had been， 主句動(dòng)詞用have been speaking）
（三）、表示與將來事實(shí)相反的虛擬條件句（對將來的事實(shí)實(shí)現(xiàn)的可能性不大）。其句子結(jié)構(gòu)為：
從句：If + 主語+ should （或were） + 動(dòng)詞原形+……
主句：主語+ would （could，should，might） + 動(dòng)詞原形+……
例如：
⑴、If I were to work at this problem，I would do it in another way.要是我來解這道難題，我會(huì)用另外一種方法的。
⑵、If you were to do such a thing again，you would be punished. 如果你再做這樣的事情，就會(huì)受到懲罰。
⑶、If I should work harder，I could make much more progress.假如我更努力學(xué)習(xí)的話，我會(huì)取得更大的進(jìn)步。（事實(shí)上我不可能努力學(xué)習(xí)）
⑷、If it should rain tomorrow，I would stay at home.如果明天下雨的話，我將待在家里。（根據(jù)天氣情況，明天不可能下雨）
⑸、If he should come，I could ask him for some advice.萬一他來了，我就能夠向他請教。（事實(shí)上他來的可能性很?。?BR> ⑹、If he came tomorrow，I would do it with him.如果明天他來的話，我將和他一起做此事。（事實(shí)上他來的可能性很小）
⑺、 If it should rain，the crops would be saved.（從句動(dòng)詞用should rain，主句動(dòng)詞用be）如果天下雨，莊稼可能就收獲了。
⑻、 If he were to go fomorrow，he might tell you.（從句動(dòng)詞用were to，主句動(dòng)詞用tell）如果明天他走的話，他可能會(huì)告訴你。
⑼、 If he were here，I would give him the books.（從句動(dòng)詞用were，主句動(dòng)詞用give）如果他在這兒，我可能會(huì)把書給他。
注意：如果動(dòng)作在進(jìn)行中，從句（不是主句喔）要用："If + 主語+ 過去進(jìn)行式動(dòng)詞 +……"
⑽、 If she were staying here now，I would let her ride my horse.（從句動(dòng)詞用were staying， 主句動(dòng)詞用let）如果她現(xiàn)在留在這兒，我可能會(huì)讓她騎我的馬。
三、混合條件句——主從句時(shí)間不一致情況下的虛擬語氣
有時(shí)條件從句中的動(dòng)作和結(jié)果與主句中的動(dòng)作，發(fā)生的時(shí)間不一致，這時(shí)動(dòng)作的形式應(yīng)根據(jù)它所表示的時(shí)間加以調(diào)整。如：
1. 從句表示過去，主句表示將來：
⑴、If they had started the early morning yesterday，they would be here now.
⑵、If we hadn' t made adequate preparations，we shouldn' t dare to do the experiment next week.
2. 從句表示將來，主句表示過去：
⑴、If I were not to make a preparation for my experiment this afternoon，Iwould have gone to see the film with you last night.
3.從句表示過去，主句表示將來：
⑴、If we hadn't made adequate preparations，we shouldn't dare to do theexperiment next week.
4.從句表示將來，主句表示現(xiàn)在：
⑴、If we shouldn't have an exam this afternoon，I would go shopping now.
5.從句表示過去，主句表示現(xiàn)在。
⑴、If they had stared the early morning yesterday，they would be here now.
⑵、If you had followed my advice，you would be able to finish the work now.
如果你當(dāng)時(shí)聽了我的話，現(xiàn)在就能完成這份工作了。（從句說明過去，主句說明現(xiàn)在。）
6.從句表示現(xiàn)在，主句表示過去
⑴、If I were you，I would have gone to her birthday party.如果我是你，我就去參加她的生日晚會(huì)了。（從句說明現(xiàn)在，主句說明過去。）
7.從句表示過去，主句表示過去和現(xiàn)在
⑴、If you hadn‘t lent me some money，I couldn’t have bought the new house and most likely I would be still living in the dangerous house now.
假若你不借錢給我，我不可能買下這幢新房，很可能現(xiàn)在還住在危房里。（從句說明過去，主句說明過去和現(xiàn)在。）
四、含蓄條件句
非真實(shí)條件句中的條件從句有時(shí)不表出來，只暗含在上下文中，這種句子叫做含蓄條件句。含蓄條件句大體有三種情況；
1. 條件暗含在短語中。如：
（1）、What would I have done without you？如沒有你，我會(huì)怎么辦呢？（條件暗含在分詞短語without you中）
（2）、It would be easier to do it this way. 這樣做會(huì)比較容易。（條件暗含在不定式短語to do it this way中）
（3）、This same thing， happening in wartime，would lead to a disaster. 同樣的事，如發(fā)生在戰(zhàn)時(shí)，就會(huì)釀成大禍。（條件暗含在分詞短語happening in wartime中）
（4）、But for your help we couldn‘t have succeeded in the experiment. 如果沒有你的幫助，我們的實(shí)驗(yàn)是不會(huì)成功。（暗含條件是but for your help）
（5）、He must have the strength of a hippopotamus，or he never could have vanquished that great beast. 他一定是力大如河馬，否則他絕不會(huì)擊敗那只龐大的野獸。（暗含條件是連詞or）
（6）、Alone，he would have been terrified. 如是單獨(dú)一人，他是會(huì)感到害怕的。（暗含條件是alone）
2. 條件暗含在上下文中。如：
（7）、You might stay her forever. 你可以永遠(yuǎn)待在這兒。（可能暗含if you wanted to）
（8）、We would have succeeded. 我們本來是會(huì)成功的。（可能暗含if we had kept trying）
（9）、Your reputation would be ruined. 你的名譽(yù)會(huì)敗壞的。（可能暗含if you should accept it）
（10）、I would appreciate a little of your time. 謝謝你給我一點(diǎn)時(shí)間吧。（可能暗含if you were so kind as to give me a little of your time）
3. 在不少情況下，虛擬式已變成習(xí)慣說法，很難找出其暗含的條件。如：
（11） 、You wouldn‘t know. 你不會(huì)知道。
（12） 、I would like to come. 我愿意來。
（13） 、I wouldn‘t have dreamed of it. 這是我做夢也不會(huì)想到的。
（14） 、He told the story in such minute detail that he might himself have been an eye-witness. 他將那事講的非常仔細(xì)，簡直就象他親眼看見一樣。
五、條件從句中省略if 采用倒裝語序的情況
1、在if引導(dǎo)的表示虛擬的條件狀語從句中，有時(shí)可以把含有助動(dòng)詞、情態(tài)動(dòng)詞、be或have的虛擬條件句中的連詞if 省去，而將had ，should，were 等詞提到主語之前，即用倒裝結(jié)構(gòu)。
例如：
1）、原句：If she were younger， she would do it.
去If：Were she younger，she would do it. （把動(dòng)詞were移到主語she的前面）
2）、原句：If he had tried it，he could have done it.
去If：Had he tried it，he could have done it.（把had移到主語he的前面）
3）、Had he worked harder，he would have got through the exams.
4）、Were he to leave today，he would get there by Friday.
5）、Were I in your place，I wouldn‘t do that.
6）、Had I seen the film，I would have discussed it with them last night.
假如我看了那部電影，昨晚我就可以和他們一起討論了。
7）、Were I a bird，I could fly freely.
假如我是一只小鳥，我就能自由翱翔。
8）、Should it rain next week the farmers would have a good harvest.
要是下周能下雨的話，農(nóng)民們就能有個(gè)好收成了。
2、如果虛擬條件句中有were，had或should時(shí)，把它們放在if的位置上；但是如果條件句中沒有were，had或should不能用倒裝。例如：
⑴、Should it rain tomorrow，what should we do？要是明天下雨的話，我們怎么辦呢？
⑵、Were I you， I would have asked him for some advice.要是我是你的話，我就向他請教了。
⑶、Were he to do this work by himself，he would get a lot of money.如果他自己能夠做此工作，他就會(huì)得到一些錢。
3、在“開放式條件句”（open conditional clause）和讓步狀語從句中should是被省略了的。在這種情況下，如果if省略，動(dòng)詞be與主語的位置要倒裝。如：
⑴、If any person be guilty of a crime，the court shall have the right to appeal. （任何人犯罪，法院有權(quán)起訴。）
Be any person guilty of a crime，the court shall have the right to appeal.
⑵、Whether she be right or wrong，she will have my unanswering support. （不管她是對還是錯(cuò)，我都會(huì)支持她的。）
Be she right or wrong，she will have my unanswering support.
⑶、____ ，I will take her as my wife.
［A］Were she rich or poor
［B］Being rich or poor
［C］Be she poor or rich
［D］Whether is she poor or rich
4、注意：有時(shí)虛擬條件句并沒來if 從句表示出來，而是用介詞短語（otherwise，or，without，but for）、上下文或其它方式來表示。
⑴、We didn't know his telephone number；otherwise we would have telephoned him.
⑵、Without you help，I wouldn‘t have achieved so much.
⑶、But for your help，I would not have succeeded.
六、有時(shí)虛擬條件句的從句或主句都可以省略其中一個(gè)：
1. I could help you. （只有主句）
2. If I had time. （只有從句）
3. She should have come to the meeting. （只有主句）
4. If he had much more money. （只有從句）
第二節(jié)：其他形式的條件句中的虛擬語氣
一、用“without/but for/in the absence of ”表示“要不是”，“如果沒有”（相當(dāng)于if it were not for…）表示條件時(shí)，句中一般用虛擬語氣。（也可用陳述語氣）
Without your help，I couldn' t finish my work on time.
In the absence of water and air，nothing could live.
二、由“providing （that）/ provided （that）/on condition that/ in order that“引導(dǎo)的條件從句或目的從句，根據(jù)情況，可用虛擬語氣。（有時(shí)也可用陳述語氣）
They are willing surrender provided they are given free passage.
三、用without / but for / in the absence of 表示"要不是"、"如果沒有"，表示條件虛擬句：
（1）、Without air，nothing could live.要是沒有空氣，什么也不能生存。
（2）、But for your assistance，we could not accomplish it.要不是你的幫忙，我們是難有成就的。
（3）、In the absence of water and air，nothing could live.如果沒有水和空氣，什么也不能生存。
第五部分：其他幾種情況下的虛擬語氣
第一節(jié)：虛擬語氣在as if / as though 引導(dǎo)的方式狀語從句中的應(yīng)用
虛擬語氣在as if / as though 引導(dǎo)的方式狀語從句中，謂語動(dòng)詞形式與wish后的賓語從句基本相同
1.表示與現(xiàn)在事實(shí)相反或?qū)ΜF(xiàn)在情況有懷疑，謂語動(dòng)詞用過去式。例如：
（1）、.He felt as if he alone were responsible for what had happened.他感到仿佛唯獨(dú)他要對發(fā)生的一切負(fù)責(zé)。
（2）、He acts as if he were / was a TV expert.他做起事來好象是個(gè)電視專家。
（3）、Alan talked about Rome as if he were a Roman.艾倫談起羅馬來好像他是個(gè)羅馬人一樣。
（4）、John pretends as if he didn' t know the thing at all，but in fact he knows it very well.（用過去式表示與現(xiàn)在事實(shí)相反的假設(shè)）
（5）、He pretends as if he didn't know the thing at all，but in fact he knows it very well.（用過去式表示與現(xiàn)在事實(shí)相反的假設(shè)）他假裝好象完全不懂那事，其實(shí)他對那事非常了解。
2. 表示過去想象中的動(dòng)作或情況，謂語動(dòng)詞用過去完成式。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
那棵樹看上去好象很久沒人給澆水了。（答案是c）
（2）、The old man looked at the picture，he felt as though he had gone back to time 20 years ago.（用過去完成式表示與過去相反的事實(shí)）
（3）、The old man looked at the picture，he felt as though he had gone back to time 20 years ago.（用過去完成式表示與過去相反的事實(shí)）那老人看著照片，他覺得仿佛回到20年前的時(shí)光。
3.表示與將來事實(shí)相反：
（1）、They talked and talked as if they would never meet again （would+動(dòng)詞原形，表示與將來事實(shí)相反）
（2）、They talked and talked as if they would never meet again.（would + 原形動(dòng)詞meet，表示與將來事實(shí)相反）他們談了又談，仿佛他們不會(huì)再相見的樣子。
注：在as if / as though 句中，如果有可能成為事實(shí)，用陳述語氣。
He looks as if he is going to be ill.
第二節(jié)：虛擬語氣用在lest，for fear that及in case引導(dǎo)的目的狀語從句中
在由lest等引導(dǎo)的目的狀語從句中需用虛擬語氣，表示“以防，以免”等意思，其謂語動(dòng)詞多由should ＋動(dòng)詞原形構(gòu)成，should也可省略。
例如：
⑴、He was punished lest he should make the same mistake again.他被處以懲罰以免他再犯。
⑵、The mad man was put in the soft-padded cell lest he _____ himself.
a. injure b. injured c. had injure d. would injure
這個(gè)瘋子被關(guān)進(jìn)墻上裝有襯墊的病房，以免傷了他自己。（答案是a）
第三節(jié)：介詞短語表示虛擬
有時(shí)假設(shè)的情況并不以條件從句表示出來，而是通過一個(gè)介詞短語來表示，或通過上下文或其他方式表示出來。如but for，but that…，in case of，otherwise，supposing，under more favourable condition，without 等表示讓步假設(shè)。
1）、He worked very hard； otherwise he might have failed. （他刻苦工作，不然他就失敗了。）
2）、We could have done better under more favorable conditions.（假設(shè)我們有更有利條件，我們還會(huì)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
第四節(jié)：虛擬語氣用在It is（about ／high）time ＋that定語從句中
在It is（about／high）time ＋that定語從句中需用虛擬語氣，表示“該做……的時(shí)候了”，其動(dòng)詞形式用一般過去時(shí)或should ＋動(dòng)詞原形。
（1）、It's already 5 o'clock now.Don't you think it's about time we went home？現(xiàn)在已經(jīng)5點(diǎn)鐘了，你不認(rèn)為我們應(yīng)該回家了嗎？
（2）、It is about time you were in bed.
（3）、It is high time we left.
（4）、It is the first time I came here.
注：
1、在this is the first time ／second time that.……句型中，從句中謂語動(dòng)詞用陳述語氣完成時(shí)態(tài)。
例如：
Is this the first time that you have visited Hongkong？這是你第一次參觀香港嗎？
2、It's time to do something有別于It's time that.……
第五節(jié)：在if only 引起的感嘆句中需用虛擬語氣
謂語動(dòng)詞用過去式或過去完成式（謂語動(dòng)詞與wish賓語從句的虛擬形式相同）。
⑴、If only he didn‘t drive so fast?。ìF(xiàn)在）
⑵、If only she had asked someone‘s advice.（過去）
⑶、If only the rain would stop.（將來）
例題解析：
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 引出感嘆句，意思是“要是……多好”，表示說話人的一種愿望，希望發(fā)生（事實(shí)上不可能發(fā)生）與過去事實(shí)相反的情況。本句的全句意思是：“看我現(xiàn)在的處境多糟糕！要是我聽從你的勸告多好”。事實(shí)上，句中的“我”沒有聽從勸告，所以處境很糟糕。
題中空格處應(yīng)當(dāng)用虛擬語氣，答案是B.