英語有三種語氣，即陳述語氣,、祈使語氣和虛擬語氣

1. 真實條件句和非真實條件句

條件句有真實條件句和非真實(虛擬)條件句兩種,。真實條件句所表示的假設(shè)是有可能發(fā)生的，而非真實條件句則通常表示一種假想,，與事實相反或不大可能會發(fā)生：

If I have time, I will go with them. 假若我有時間,，我就同他們?nèi)ァ?陳述語氣)

If I were you, I would go with them. 假若我是你，我就同他們?nèi)ァ?虛擬語氣)

2. 虛擬條件句的三種基本類型

(1) 若與現(xiàn)在事實相反,，條件從句的謂語用過去式(be通常用were),，主句謂語用“should (would, could, might)+動詞原形”：

If you took a taxi，you’d get there quicker. 如果你坐出租車去,，你可以快一點到那里,。(但你沒有坐出租車)

If I knew her number I could ring her up. 要是我知道她的電話號碼，我就可以給她打電話了,。(可惜我不知道)

(2) 若與過去事實相反,，條件從句的謂語用過去完成時(had+過去分詞)，主句謂語用“should (would, could, might)+have+過去分詞”：

If I had left sooner,，I would have been on time. 要是我早點動身,，我就準(zhǔn)時到了。(但我動身太遲了) 【I had left縮寫I’d left,；I would have been縮寫為I’d have been】

If we had found him earlier we could have saved his life. 要是我們當(dāng)時早點找到他的話,，我們就可以救活他。(可惜我們找到他太晚了)

(3) 若與將來事實相反：條件從句a)If+主語+動詞過去式;b)If+主語+were to+動詞原形;c)If+主語+should+動詞原形(注意不能是would) ,。主句謂語用“should (would, could, might)+動詞原形”：

If you came tomorrow, we would have the meeting.

If it were to rain tomorrow, we would put off the sports meeting.

If he should not come tomorrow, we should put off the meeting till next Monday.

3. 錯綜時間虛擬條件句

所謂錯綜時間虛擬條件句即條件從句與主句所指時間不一致,，如從句指過去，而主句即指的是現(xiàn)在或?qū)?，此時應(yīng)根據(jù)具體的語境情況,，結(jié)合上面提到的三種基本類型對時態(tài)作相應(yīng)的調(diào)整：

If it had rained last night, the ground would be wet now. 要是昨晚下過雨的話，現(xiàn)在地面就會是濕的,。

You would be much better now if you had taken my advice. 假若你當(dāng)時聽我的話,，你現(xiàn)在就會好多了。

注：條件從句用 if I were…時,，既可指現(xiàn)在也可指過去,。

If I were you, I would go. 假若我是你，我就去,。

If I were not busy, I would have come. 假若我不忙,，我早就來了。

也可用 if I had been you也表示過去：

If I had been you,，I’d have taken the job. 我要是你,，我就接受那份工作了,。

4. 含蓄虛擬條件句

所謂含蓄虛擬條件句即指將條件從句隱藏在上下文一定的短語中的一類條件句：

(a) 將條件隱含在某些連詞(如or, or else, otherwise等)中：

I didn’t know that he was a cheat, or else I wouldn’t have believed him=I wouldn’t have believed him, but I didn’t know that he was a cheat= If I had known he was a cheat, I wouldn’t have believed him. 我不知道他是個騙子，不然我也不會相信他了,。

I’m really very busy, otherwise I would certainly go there with you. 我真的是太忙了,，不然我就會同你一道去了。

(b)If it weren’t for與if it hadn’t been for,。這是兩個很常用的虛擬語氣句型,，其意為“若不是(有)”、“要不是有”：if it weren’t for 用于談?wù)摤F(xiàn)在的情況,，而if it hadn’t been for 用于談?wù)撨^去的情況,。

If it weren’t for water, no plant could grow. 要是沒有水植物就無法生長,。

If it hadn’t been for the doctor, he would have died. 要不是醫(yī)生救了他,，他就會死了。

注：(1) 此句型有可用but for, without等替換：

If it hadn’t been for [But for, 或者Without] your assistance,， we wouldn’t have succeeded. 要不是有你幫忙,，我們是不會成功的。

(c) 將條件隱含在介詞短語中：

Without air, no one could live. 沒有空氣,，人就不能活,。(=If there were no air, no one could live.)

But for his help, he would have failed. 要不是有他的幫助，他就會失敗了,。(=It it hadn’t been for his help, he would have failed.)

 (d)將條件隱含在分詞短語中：

Born in better times, he would have been a scholar. 如果出生在好時代,，他早就成為學(xué)者了。(=If he had been born in better times, he would have been a scholar…)

Failing this time, what would you do,？假若這次失敗,，那你怎么辦？(=If you failed =this time, what…)

Walking alone in the dark, Mary would be terrified. 要一個人單獨在黑暗中走,，瑪麗會感十分害怕,。(If Mary walked alone in the dark, she…)

 (e) 將條件隱含在名詞短語中：

A true friend would not have betrayed me. 若是真正的朋友，就不會背棄我,。(=If he had been a true friend, he would…)

A few hours earlier, and you would have seen the famous writer. 要是你早來幾個小時,，你就見到這位著名的作家了。(If you had come a few hours earlier, you…)

(f) 將條件隱含在定語從句中：

Anyone who had seen that painting might have taken it for a photo. 凡是看過那畫的人,，都可能把它看成是照片,。(=If anyone had seen that painting，he might have taken it for a photo)

5. 幾類省略的虛擬條件句型

(1) 省略連詞if,。有時可將條件從句的連詞if省略,，但此時應(yīng)用倒裝句型，即將從句中的were, should, had 等提到句首：

Were I Tom, I would refuse. 如果我是湯姆,，我會拒絕,。

Had it not been for the bad weather we would have arrived in time. 若不是天氣壞,，我們就準(zhǔn)時到達了。

注：① 若條件從句為否定句,，否定詞not應(yīng)置于主語之后,，而不能與were, should, had 等縮略成Weren’t, Shouldn’t, Hadn’t而置于句首。比如：Were I not Tom, I would refuse./Should it not rain tomorrow, I would go shopping.

② 有時省略if后提前的had不是助動詞：

Had I time, I would come. 假若我有時間,，我會來的,。(=If I had time…)

(2) 省略條件句的主語和其后的動詞be。若主從句主語一致,，且謂語部分包含有動詞be,，通常可將主語和動詞be省略：

If repaired earlier, the tractor would not have broken down. 要是早點兒修一下,，拖拉機就不會拋錨了,。(=If it had been repaired earlier…)

(3) 省略“it+be”：

If necessary, I would send more farm-hands to help you. 如果需要的話我會派更多的民工去你。(=If it is necessary...)

1. wish后的賓語從句用虛擬語式

要表示與現(xiàn)在事實相反的愿望,，從句謂語一般過去時或過去進行時,，表示與過去相反的愿望，從句謂語用過去完成時或would / could+have +過去分詞,，表示將來沒有把握或不太可能實現(xiàn)的愿望,，用would (could)＋動詞原形：

I wish I were rich. 要是我現(xiàn)在有錢就好了。

I wish I were better looking. 要是我長得漂亮些就好了,。

She wished she had stayed at home. 她后悔的是她當(dāng)時要是留在家里就好了,。

I wish I had been rich. 要是那時我有錢就好了。

I wish you would go with us tomorrow. 要是你明天同我們一起去就好了,。

2. if only的句子后用虛擬語氣

if only 與 I wish一樣,，也是表示與事實相反的愿望的，其后所虛擬語氣的時態(tài)與 wish后所接時態(tài)的情況相同：注：if only 通常獨立使用,，沒有主句,。

If only I were better looking. 要是我長得漂亮些就好了。

If only I had listened to my parents! 我要是當(dāng)時聽了父母的話就好了,。

If only she would go with me! 她要是愿意和我一道去就好了!

3. as if (as though) 從句中的虛擬語氣

以as if (as though)引導(dǎo)的方式狀語從句或表語從句,，有時用虛擬語氣，若表示與現(xiàn)在事實相反,，謂語動詞用一般過去時,；若表示與過去事實相反，用過去完成時,；表示將來的可能性不大,，用would (might, could)+動詞原形：

He acts as if he knew me. 他顯得認識我似的。

They treat me as though I were a stranger.  他們待我如陌生人,。

He talks as if he had been abroad. 他說起話來好像曾經(jīng)出過國,。

注：從句所表示的內(nèi)容若為事實或可能為事實,，也可用陳述語氣：

It looks as if we’ll be late. 我們似乎要遲到了。

This meat tastes as if it has already gone bad. 這肉吃起來似乎已經(jīng)壞了,。

4. It is time 后的定語從句用虛擬語氣

從句謂語通常用過去式表示現(xiàn)在或?qū)?，有時也用過去進行時或“should+動詞原形”(較少見，且should不能省略),，其意為“(早)該干某事了”：

I think it’s time you went to bed. 我想你該睡覺了,。

It’s time we went [were going, should go]. 我們該走了。

注：(1) time前有時有about和high修飾：

It’s high/about time you bought a new car. 你該買輛新車了,。

(2) 與其他的虛擬結(jié)構(gòu)不同,，該結(jié)構(gòu)不能在該用was時而用were：

It’s time I was in bed. 我該上床睡了。(不用were)

5. would rather后的句子用虛擬語氣

通常用一般過去時表示現(xiàn)在或?qū)淼脑竿?，用過去完成時表過去的愿望：

I’d rather you went tomorrow (now). 我寧愿你明天(現(xiàn)在)去,。

I’d rather you hadn’t said it. 我真希望你沒有這樣說過。

6. 某些用虛擬語氣的賓語從句

在表示“堅持”,、“命令”,、“建議”、“要求”等后的賓語從句要用虛擬語氣,。這類動詞有人歸納為“一個堅持(insist)、兩個命令(order, command),、三個建議(advise, suggest, propose),、四個要求(demand, require, request, ask)”，這類虛擬語氣由“should+動詞原形”構(gòu)成,，其中的should在美國英語中通?？梢允÷裕篬對應(yīng)的名詞有：某人的order, command, advice, suggestion, proposal, demand, requirement, request等+is that sb (should) do sth/sth (should) be done (should) not be done ]

He insisted that I (should) go with them. 他堅持要我同他們一起去。

He ordered that it (should) be sent back. 他命令把它送回去,。

The doctor advised [suggested] that he (should) not smoke. 醫(yī)生建議他不要抽煙,。

He requires that I (should) appear. 他要求我出場。

注：(1) 其中引導(dǎo)賓語從句的that通常不省略,。

(2) 這類句子有時可用于被動結(jié)構(gòu),，前面用先行詞it作主語，代表后面的從句：

It was proposed that this matter be discussed next time. 有人提議這事下次再討論,。

(3) 動詞insist后接賓語從句時,，除可用虛擬語氣外，也可用陳述語氣,，兩者的區(qū)別是：若謂語動詞所表示的動作尚未發(fā)生,，或尚未成為事實，則用虛擬語氣,；若謂語動詞所表示的動作已經(jīng)發(fā)生,，或已經(jīng)成為事實,，則要用陳述語氣。比較：

He insisted that I had read his letter. 他堅持說我看過他的信,。

He insisted that I should read his letter. 他堅持要我看他的信,。

(4) 與動詞insist相似，動詞suggest后接賓語從句時,，除可用虛擬語氣外,，也可用陳述語氣，兩者的區(qū)別也是：若謂語動詞所表示的情況尚未成為事實,，則用虛擬語氣,，此時suggest通常譯為“建議”；若謂語動詞所表示的情況為既成事實,，則要用陳述語氣,，此時的suggest通常譯為“表明”、“認為”,。比較并體會：

He suggested that we (should) stay for dinner. 他建議我們留下吃飯,。

What he said suggested that he was a cheat. 他說的話表明他是個騙子。

I suggested that you had a secret understanding with him. 我覺得你與他心照不宣,。

(5) 以上動詞用作名詞或派生出的名詞時,，相應(yīng)的主語從句、表語從句或同位語從句也用虛擬語氣：

His demand is that we (should) set off at once. 他要求我們馬上出發(fā),。

He made the demand that we (should) set off at once. 他要求我們馬上出發(fā),。

(6) 在現(xiàn)代英語中，以上動詞(包括其名詞形式以及其派生名詞)有時也可不用虛擬語氣(但初學(xué)者宜慎用)：

Her suggestion was we had our conversation in French. 她的建議是我們用法語交談,。

He said that he would not be long and suggested that we waited for him. 他說他不會去很久,，并建議我們等他。

7. 某些用虛擬語氣的主語從句

形容詞important, impossible, necessary, strange,  essential（基本的）, vital（重要的）, advisable（ 明智的,，可取的）, urgent(緊急的), desirable（值得擁有的）, natural, imperative（必要的）等后的主語從句通常用虛擬語氣：

It is impossible that he should go home. 他不可能會回家去,。

It is necessary that I should return it right now. 我有必要馬上還回去。

注：在It is amazing (strange, surprising, astonishing, a pity, a shame)以及 I am surprised (sorry) 和I regret等結(jié)構(gòu)后的that 從句中有時也用should,，表示說話人的驚異,、懊悔、失望等情感,，常含有“竟然”之意,。如：

It’s strange that he should be so rude. 他竟如此無禮，真是奇怪,。

I’m surprised that he should have failed. 他竟然失敗了,，這使我很吃驚。

It is a pity that you （should ）fail the exam.

It’s a pity that he should have failed the exam. 他考試竟沒及格,，真是遺憾,。

It is no wonder he (should)be late for class.

1. If he was here, he _______ us how to do it.

A. told                      B. would tell             C. had told                D. had told

2. If we _____ 200 years old, we _____ everything.

A. were to be, could change                       B. had been, changed

C. were, would have changed                     D. should be, changed

3. If your father ______this, he would be angry.

A. knows                  B. knew                    C. had known            D. would know

4._______ your address, I would have written to you.

A. Did I know           B. Were I to know C. Had I known             D. If I should know

5.______ he fail, he would kill himself.

A. Should                 B. Would                  C. Had                      D. If

6. The doctor insisted that I ______ the medicine, but I insisted that I ______ ill.

A. take, wasn’t          B. should take, be      C. take, should be      D. took, should be

7.I wish you _______ him my telephone number, but you did.

A. didn’t give            B. hadn’t given          C. wouldn’t give        D. shouldn’t give

8. “Shall I open the window?” “I’d rather you ______.”

A. can’t                    B. won’t                   C. didn’t                   D. hadn’t

9. It’s already 12 o’clock. It’s high time you ____to bed.

A. went                    B. had gone               C. would go              D. go

10. I’m really busy, or I ____ with you.

A. will go                 B. went                     C. would go              D. have gone

11. It was lucky. Meeting anywhere else, we ____ each other.

A. couldn’t have recognized                       B. hadn’t recognize

C. couldn’t recognized                               D. didn’t recognize

12. It’s possible that he _____ us some money, but it’s impossible that he _____ us so much.

A. will lend, will lend   B. will lend, should lend C. should lend, will lend    D. should lend, should lend

13. Thank you very much indeed. If it had not been for your advice I really _____ what I should have done.

A. don’t know           B. didn’t know          C. hadn’t known        D. wouldn’t have known

14. “It looks as if he were drunk.” “So it does. _____.”

A. He’d better give up drinking                  B. He shouldn’t have drunk so much

C. Health is more important than drink        D. I wonder why he is always doing so

15. “Mary looks hot and dry” “So _____ you if you had a high fever.”

A. do                        B. are                       C. will                      D. would          

參考答案：1—5 BABCA  6—10 BBCAC  11—15 ABADD