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虛擬語(yǔ)氣
1. 表示現(xiàn)在/過去/將來情況的虛擬條件句
虛擬條件句主要有三種結(jié)構(gòu)：
1) 表示與現(xiàn)在情況相反：主句謂語(yǔ)用“would / could / might +動(dòng)詞原形”，從句謂語(yǔ)用“動(dòng)詞的一般過去時(shí)”(動(dòng)詞be的過去式一律用were)。
If I were you, I would not accept his offer.
If I had time, I would certainly go to the cinema with you.
2) 表示與過去情況相反：主句謂語(yǔ)用“would / could / might + have +過去分詞”，從句謂語(yǔ)用過去完成時(shí)。
If I had got up a little earlier, I wouldn’t have missed the train.
If I had been more careful, I might have passed that exam.
3) 表示與將來情況相反：主句謂語(yǔ)用“would / could / might +動(dòng)詞原形”，從句謂語(yǔ)用“were +動(dòng)詞不定式”或“should +動(dòng)詞原形”。
If I were to do the job, I would not be able to have enough time to study.
If it should rain tomorrow, I would not go out with you.
2. 虛擬條件句連接詞if的省略
如果虛擬條件句的從句中含有were, had, should, could等詞時(shí)，可以省略連接詞if，但這時(shí)必須把were, had, should, could等詞移到主語(yǔ)前面，形成倒裝。這種句型主要用于書面形式。
Were I to do the job, I would finish doing it within two weeks.
Had it not been for his help, we couldn’t have arrived there on time.
Should it rain tomorrow, I would stay at home.
3. wish后賓語(yǔ)從句中的謂語(yǔ)構(gòu)成
動(dòng)詞wish后的賓語(yǔ)從句表示未實(shí)現(xiàn)的或不可能實(shí)現(xiàn)的愿望，其賓語(yǔ)從句中的謂語(yǔ)動(dòng)詞要用虛擬語(yǔ)氣，有以下三種構(gòu)成形式。
1) 表示現(xiàn)在不可能實(shí)現(xiàn)的愿望，賓語(yǔ)從句中的謂語(yǔ)動(dòng)詞用一般過去時(shí)。(be的過去式為were)。
I wish I had enough money to buy a car.
I wish I were as young and energetic as you.
2) 表示過去未能實(shí)現(xiàn)的愿望，賓語(yǔ)從句中的謂語(yǔ)動(dòng)詞用過去完成時(shí)(had +過去分詞)或“would / could + have +過去分詞 ”。
I wish I hadn’t made such a mistake.
I wish I could have done it better.
3) 表示將來不可能實(shí)現(xiàn)的愿望，賓語(yǔ)從句中的謂語(yǔ)動(dòng)詞用“would / should (could, might) +動(dòng)詞原形”。
I wish I would not get old.
I wish I could travel around the world one day.
4. 某些動(dòng)詞后的賓語(yǔ)從句中謂語(yǔ)動(dòng)詞要用虛擬語(yǔ)氣
在一些動(dòng)詞后面的賓語(yǔ)從句中，謂語(yǔ)動(dòng)詞要用虛擬語(yǔ)氣。這時(shí)，謂語(yǔ)動(dòng)詞用動(dòng)詞原形或should +動(dòng)詞原形。這類動(dòng)詞一般表示命令，要求，決定，建議，主張等概念，主要有：advise, ask, command, decide, demand, desire, direct, insist, move, order, propose, recommend, request, require, suggest,等。
The workers demanded that their wages (should) be raised by 10 per cent.
The teacher decided that you do the experiment first.
5. 某些名詞后的表語(yǔ)從句和同位語(yǔ)從句中謂語(yǔ)動(dòng)詞要用虛擬語(yǔ)氣
在一些名詞后面的表語(yǔ)從句和同位語(yǔ)從句中，謂語(yǔ)動(dòng)詞要用虛擬語(yǔ)氣。這時(shí)，謂語(yǔ)動(dòng)詞用動(dòng)詞原形或should +動(dòng)詞原形。這類名詞一般表示命令，要求，決定，建議，主張等概念，主要有：advice, idea, instruction, motion, order, plan, proposal, recommendation, request, requirement, suggestion,等。
My suggestion is that we (should) send for a doctor immediately.
He gave the order that they (should) do the experiment again.
6. 錯(cuò)綜時(shí)間條件句
條件從句表示的動(dòng)作和主句表示的動(dòng)作，有時(shí)發(fā)生的時(shí)間是不一致的.如從句是對(duì)過去情況的假設(shè)，而主句可能是對(duì)現(xiàn)在正在進(jìn)行情況的假設(shè)。 這種句子稱為錯(cuò)綜時(shí)間條件句.
If the weather had been more favourable, the crops would be growing still better.
7. 某些主語(yǔ)從句中的謂語(yǔ)動(dòng)詞要用虛擬語(yǔ)氣
某些表示命令，要求，決定，建議，主張以及“重要性”和“緊迫性”等概念的主語(yǔ)從句中謂語(yǔ)動(dòng)詞要用虛擬語(yǔ)氣。這時(shí)，謂語(yǔ)動(dòng)詞用動(dòng)詞原形或should +動(dòng)詞原形。這類主語(yǔ)從句一般由 “It is (was) + 形容詞/過去分詞 + that引導(dǎo)的從句”構(gòu)成。該結(jié)構(gòu)中，常用的形容詞主要有：advisable, appropriate, desirable, essential, imperative, important, necessary, obligatory, proper, urgent, vital等;常用的過去分詞主要有：arranged, decided, demanded, desired, ordered, proposed, recommended, requested, suggested等。
It is necessary that you (should) stop smoking so heavily.
It is arranged that you (should) enter for this competition.
8. as if / though引起的從句
當(dāng)as if / though引起的從句所表達(dá)的內(nèi)容完全與實(shí)際情況相反或者純粹是一種假設(shè)時(shí)，通常要用虛擬語(yǔ)氣。如果從句表示與現(xiàn)在的事實(shí)相反，謂語(yǔ)動(dòng)詞用一般過去時(shí);如果從句表示與過去的事實(shí)相反，謂語(yǔ)動(dòng)詞用過去完成時(shí);如果從句表示與將來的事實(shí)相反，謂語(yǔ)動(dòng)詞用would (might, could) + 動(dòng)詞原形;
They talked as if they had been friends for years.
I remember the whole thing as if it happened yesterday.
It looks as if it might rain.
Note: 如果as if / though引起的從句所表達(dá)的內(nèi)容被看作是事實(shí)或者有可能是真實(shí)的，則要用陳述語(yǔ)氣。
It seems as if it is going to rain.
The meat tastes as if it has already gone bad.
9. lest, for fear that和 in case引起的從句
當(dāng)lest, for fear that和 in case表示“以免，以防，生怕，惟恐”等時(shí)，在它們引起的從句中，謂語(yǔ)動(dòng)詞常用should + 動(dòng)詞原形。
He ran away lest he should be seen.
He’s working hard for fear that he should fall behind.
He left early in case he should miss the last train.
10. If only引出的從句
If only引出的從句用以表達(dá)感嘆性的愿望，常譯為“要是…就好了”。If only從句經(jīng)常省略結(jié)果主句，且主要用在虛擬語(yǔ)氣中，即從句的謂語(yǔ)動(dòng)詞用一般過去時(shí)表示現(xiàn)在或?qū)聿豢赡軐?shí)現(xiàn)的愿望，或用過去完成時(shí)表示過去沒有實(shí)現(xiàn)的愿望。
If only the rain would stop.
If only I’d listened to my parents.
Note: if only引出的句子偶爾也可使用陳述語(yǔ)氣，但考生須注意的是，在各類測(cè)試中一般都以用虛擬語(yǔ)氣為正確答案。
11. would rather(that)引出的從句
would rather意為“寧愿”，接從句時(shí)常省略關(guān)系代詞that。would rather后的從句要用虛擬語(yǔ)氣，即從句謂語(yǔ)動(dòng)詞用一般過去時(shí)表示現(xiàn)在或?qū)淼脑竿眠^去完成時(shí)表示與過去事實(shí)相反的愿望。
I’d rather you told me the truth.
I would rather you came tomorrow than today.
I’d rather you hadn’t told me about it.
12. It is (about/high) time (that) 句型
該句型表示“(早)該做…”，其后的定語(yǔ)從句中的謂語(yǔ)動(dòng)詞要用虛擬語(yǔ)氣表示。在測(cè)試中從句的謂語(yǔ)動(dòng)詞用一般過去時(shí)。
It is time that we went to bed.
It is high time that somebody taught you to behave yourself.
13. 表示猜測(cè)的幾種不同的方法及意義
一些情態(tài)動(dòng)詞與動(dòng)詞的完成式連用能夠表示對(duì)過去情況的猜測(cè)或者未實(shí)現(xiàn)的可能性。
1) could have + 過去分詞
A. 表示對(duì)過去可能發(fā)生的事情的推測(cè)，意為，“可能做了某事”。
He couldn’t have seen her yesterday.
They could have lost their way.
B. 表示某事在過去本有可能發(fā)生，但事實(shí)上并未發(fā)生，意為，“本可以做某事”。
We could have started a little earlier.
I could have killed her. It was a narrow escape.
2) may (might) have + 過去分詞
A. 表示對(duì)過去情況的推測(cè)，意為，“可能已做某事”。
He may have heard the news.
I might have come to a wrong conclusion.
B. 表示一種未實(shí)現(xiàn)的可能性，即本可以做某事，而實(shí)際上并沒有做，有時(shí)含有抱怨的口吻。
It was a narrow escape. You might have killed yourself.
A lot of men died who might have been saved.
3) must have + 過去分詞
表示邏輯上的必然性，即按照某些現(xiàn)象推斷過去肯定發(fā)生過的某事。
She must have made a big mistake.
The city at one time must have been prosperous, for it enjoyed a high level of civilization.
4) needn’t have + 過去分詞
表示過去不必做某事，但已經(jīng)做了，即本可不必做某事。
You needn’t have woken me up. I don’t have to go to work today.
He needn’t have watered the flowers, for it is going to rain.
5) should / ought to have + 過去分詞
表示過去應(yīng)該做某事而實(shí)際上沒有做。
You should / ought to have done what your parents told you. (But you failed to do it.)
You should / ought to have been more careful. (But you weren’t.)
6) shouldn’t / oughtn’t to have + 過去分詞
表示過去不應(yīng)該做某事而實(shí)際上卻做了。
You shouldn’t / oughtn’t to have crossed the road when the lights were red. (But you did.)
They shouldn’t / oughtn’t to have left so soon. (But they did.)
7) would have + 過去分詞
表示對(duì)現(xiàn)在或?qū)砟硶r(shí)之前業(yè)已完成的動(dòng)作的推測(cè)。可譯為，“可能”、“也許”、“想必”。
He would have arrived by now.
She would have recovered by then.
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