一、概说
英语有三种语气，即陈述语气、祈使语气和虚拟语气。陈述语气用于陈述事实、提出看法或问题等，祈使语气用于表示请求、命令或警告等，虚拟语气则表示假想或主观愿望：
He is honest. 他很诚实。(陈述语气)
Don’t be late next time. 下次别迟到。(祈使语气)
If I were you I wouldn’t go. 我要是你，我就会去。(虚拟语气)
I wish I had a lot of money. 要是我有很多钱就好了。(虚拟语气)
二、带虚拟条件的虚拟语气
1. 真实条件句和非真实条件句
条件句有真实条件句和非真实(虚拟)条件句两种。真实条件句所表示的假设是有可能发生的，而非真实条件句则通常表示一种假想，与事实相反或不大可能会发生：
If I have time, I will go with them. 假若我有时间，我就同他们去。(陈述语气)
If I were you, I would go with them. 假若我是你，我就同他们去。(虚拟语气)
2. 虚拟条件句的三种基本类型
(1) 若与现在事实相反，条件从句的谓语用过去式(be通常用were)，主句谓语用“should (would, could, might)+动词原形”：
If you took a taxi，you’d get there quicker. 如果你坐出租车去，你可以快一点到那里。(但你不坐)
If I knew her number I could ring her up. 要是我知道她的电话号码，我就可以给她打电话了。(可惜我不知道)
(2) 若与过去事实相反，条件从句的谓语用过去完成时(had+过去分词)，主句谓语用“should (would, could, might)+have+过去分词”：
If I’d left sooner，I’d have been on time. 要是我早点动身，我就准时到了。(但我动身太迟了)
If we had found him earlier we could have saved his life. 要是我们当时早点找到他的话，我们就可以救活他。(可惜我们找到他太晚了)
(3) 若与将来事实相反，条件从句的谓语用过去式(be通常用were)，主句谓语用“should (would, could, might)+动词原形”：
If he went，would you go too? 如果他去，你也去吗?(大概他不会去)
If I asked him，I’m sure he’d help us. 如果我向他提出要求，肯定他会帮助我们。(不过我不打算这样做)
注：① 主句谓语中的should主要用于第一人称后。would, might, could的大致区别是：would表示结果，might表示可能性，could表示能力、允许或可能性。比较：
If you tried again you would succeed. 要是你再试一试，你就会成功的。(would表结果)
If you tried again you might succeed. 要是你再试一试，你可能会成功的。(might表可能)
If you tried again you could succeed. 要是你再试一试，你就能成功了。(could表能力)
② 条件从句的谓语动词为be时，不管其主语为单数还是复数通常都用were，但在口语或非正式文体中的单数第一人称和第三人称后，也可用was，不过在 If I were you这样的表达中，通常还是以用were为宜。
③ 有时条件从句用would表示愿意：
If he would live on with me, I would be his better half. 要是他还愿意跟我过，我仍会做他的妻子。
④ 对于与将来事实相反的情形，请注意以下几点：一是这里说的与将来事实相反，实为对将来情况的推测；二是此用法中的条件从句谓语除用过去式外，有时也用“should+动词原形”(表示可能性极小，常译为“万一”)或“were to+动词原形”(表示与将来事实相反的假设)；三是当条件从句使用“should+动词原形”这样的谓语时，主句谓语除可用“should (would, could, might)+动词原形”这样的虚拟语气外，也可用陈述语气或祈使语气：
If it should rain tomorrow, don’t expect me. 万一明天下雨，就不要等我了。
I should see him, I’ll tell him. 万一我见到他，我就告诉他。
3. 错综时间虚拟条件句
所谓错综时间虚拟条件句即条件从句与主句所指时间不一致，如从句指过去，而主句即指的是现在或将来，此时应根据具体的语境情况，结合上面提到的三种基本类型对时态作相应的调整：
If it had rained last night, the ground would be wet now. 要是昨晚下过雨的话，现在地面就会是湿的。
You would be much better now if you had taken my advice. 假若你当时听我的话，你现在就会好多了。
注：条件从句用 if I were…时，既可指现在也可指过去。如：
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，我早就来了。
也可用 if I had been you也表示过去：
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. 含蓄虚拟条件句
所谓含蓄虚拟条件句即指将条件从句隐藏在上下文一定的短语中的一类条件句：
(1) 将条件隐含在不定式短语中：
I should be happy to go with you. 如果能与你一起去，我将很高兴。(=I should be happy if I could go with you.)
To have studied harder, you would have passed the examination. 你学习更用功些，你早就考及格了。(=if you have studied harder, you…)
(2) 将条件隐含在分词短语中：
Born in better times, he would have been a scholar. 如果出生在好时代，他早就成为学者了。(=If he had been born in better times, he …)
Failing this time, what would you do？ 假若这次失败，那你怎么办？(=If you failed dthis time, what…)
Walking alone in the dark, Mary would be terrified. 要一个人单独在黑暗中走，玛丽会感十分害怕。(If Mary walked alone in the dark, she…)
(3) 将条件隐含在介词短语中：
Without air, no one could live. 没有空气，人就不能活。(=If there were no air, no one could live.)
But for his help, he would have failed. 要不是有他的帮助，他就会失败了。(=It it hadn’t been for his help, he would have failed.)
(4) 将条件隐含在名词短语中：
A true friend would not have betrayed me. 若是真正的朋友，就不会背弃我。(=If he had been a true friend, he would…)
A few hours earlier, and you would have seen the famous writer. 要是你早来几个小时，你就见到这位著名的作家了。(If you had come a few hours earlier, you…)
(5) 将条件隐含在某些连词(如or, or else, otherwise等)中：
I didn’t know that he was a cheat, or else I wouldn’t have believed him. 我不知道他是个骗子，不然我也不会相信他了。(or else=if I had known he was a cheat))
I’m really very busy, otherwise I would certainly go there with you. 我真的是太忙了，不然我就会同你一道去了。(otherwise=if I were not so busy)
(6) 将条件隐含在定语从句中：
Anyone who had seen that painting might have taken it for a photo. 凡是看过那画的人，都可能把它看成是照片。(=If anyone had seen that painting…)
(7) 将条件隐含在一定的上下文中：
Don’t bother to read all these papers. It would take too long. 不要费事看所有这些文件了，那会花太多时间。(=…If you read all these papers, It would take too long)
5. if it weren’t [wasn’t] for与if it hadn’t been for。这是两个很常用的虚拟语气句型，其意为“若不是(有)”、“要不是有”：
If it weren’t for water, no plant could grow. 要是没有水植物就无法生长。
If it hadn’t been for the doctor, he would have died. 要不是医生救了他，他就会死了。
注：(1) 此句型有可用but for, without等替换：
If it hadn’t been for [But for, Without] your assistance we wouldn’t have succeeded. 要不是有你帮忙，我们是不会成功的。
(2) 原则上说，if it weren’t [wasn’t] for 用于谈论现在的情况，而if it hadn’t been for 用于谈论过去的情况。但实际上if it weren’t [wasn’t] for有时也可用于谈论过去的情况：
If it were not for their help, we couldn’t have got over the difficulties. 要不是他们帮助，这些困难我们不克服不了的。
6. 几类省略的虚拟条件句型
(1) 省略连词if。有时可将条件从句的连词if省略，但此时应用倒装句型，即将从句中的were, should, had 等提到句首：
Were I Tom, I would refuse. 如果我是汤姆，我会拒绝。
I will go, should it be necessary. 假若有必要，我会去的。
Had it not been for the bad weather we would have arrived in time. 若不是天气坏，我们就准时到达了。
注：① 若条件从句为否定句，否定词not应置于主语之后，而不能与were, should, had 等缩略成Weren’t, Shouldn’t, Hadn’t而置于句首。
② 有时省略if后提前的had不是助动词(www.yygrammar.com)：
Had I time, I would come. 假若我有时间，我会来的。(=If I had time…)
(2) 省略条件句的主语和其后的动词be。若主从句主语一致，且谓语部分包含有动词be，通常可将主语和动词be省略：
If repaired earlier, the tractor would not have broken down. 要是早点儿修一下，拖拉机就不会抛锚了。(=If it had been repaired earlier…)
(3) 省略“it+be”：
If necessary, I would send more farm-hands to help you. 如果需要的话我会派更多的民工去你。(=If it is necessary...)
(4) 省略整个条件从句。这样的省略通常需要借助一定的上下文，即省略条件从句后，所剩下的主句的意思在一定的上下文中意思是清楚的：
I might see her personally. It would be better. 我可以亲自去看她，这样好一些。(=…If I saw her personally, it would be better.)
三、七类使用虚拟语气的常见从句
1. wish后的宾语从句用虚拟语式
要表示与现在事实相反的愿望，从句谓语一般过去时或过去进行时，表示与过去相反的愿望，从句谓语用过去完成时或would / could+have +过去分词，表示将来没有把握或不太可能实现的愿望，用would (could)＋动词原形：
I wish I were [was] better looking. 要是我长得漂亮些就好了。
She wished she had stayed at home. 她后悔的是她当时要是留在家里就好了。
I wish you would go with us tomorrow. 要是你明天同我们一起去就好了。
注：从句的时态只与从句所指的时间有关，而与wish的时态无关，比较：
I wish I were rich. 要是我现在有钱就好了。
I wish I had been rich. 要是那时我有钱就好了。
I wished I were rich. 当时我后悔自己没有钱。
I wished I had been rich. 当时我后悔自己曾经没有钱。
2. if only的句子后用虚拟语气
if only 与 I wish一样，也是表示与事实相反的愿望的，其后所虚拟语气的时态与 wish后所接时态的情况相同：
If only I were [was] better looking. 要是我长得漂亮些就好了。
If only I had listened to my parents! 我要是当时听了父母的话就好了。
If only she would go with me! 她要是愿意和我一道去就好了!
注：if only 通常独立使用，没有主句。
3. as if (as though) 从句中的虚拟语气
以as if (as though)引导的方式状语从句或表语从句，有时用虚拟语气，若表示与现在事实相反，谓语动词用一般过去时；若表示与过去事实相反，用过去完成时；表示将来的可能性不大，用would (might, could)+动词原形：
He acts as if he knew me. 他显得认识我似的。
They treat me as though I were a stranger. 他们待我如陌生人。
He talks as if he had been abroad. 他说起话来好像曾经出过国。
注：(1) 从句所表示的内容若为事实或可能为事实，也可用陈述语气：
It looks as if we’ll be late. 我们似乎要迟到了。
This meat tastes as if it has already gone bad. 这肉吃起来似乎已经坏了。
在现代英语中，有时即使从句内容不是事实，也可能用陈述语气：
I feel as if [as though] I’m floating on air. 他感到好像漂浮在空中。
The stuffed dog barked as if it is [were, was] a real one. 玩具狗叫起来像真狗。
(2) 注意 It isn’t as if…的翻译：
It isn’t as if he were poor. 他不像穷的样子(或他又不穷)。
It isn’t as if you were going away for good. 又不是你离开不回来了。
4. It is time 后的定语从句用虚拟语气
从句谓语通常用过去式表示现在或将来，有时也用过去进行时或“should+动词原形”(较少见，且should不能省略)，其意为“(早)该干某事了”：
I think it’s time you went to bed. 我想你该睡觉了。
It’s time we went [were going, should go]. 我们该走了。
注：(1) time前有时有about和high修饰：
It’s high time you bought a new car. 你该买辆新车了。
(2) 与其他的虚拟结构不同，该结构不能在该用was时而用were：
It’s time I was in bed. 我该上床睡了。(不用were)
5. would rather后的句子用虚拟语气
通常用一般过去时表示现在或将来的愿望，用过去完成时表过去的愿望：
I’d rather you went tomorrow (now). 我宁愿你明天(现在)去。
I’d rather you hadn’t said it. 我真希望你没有这样说过。
6. 某些用虚拟语气的宾语从句
在表示“坚持”、“命令”、“建议”、“要求”等后的宾语从句要用虚拟语气。这类动词有人归纳为“一个坚持(insist)、两个命令(order, command)、三个建议(advise, suggest, propose)、四个要求(demand, require, request, ask)”，这类虚拟语气由“should+动词原形”构成，其中的should在美国英语中通常可以省略：
He insisted that I (should) go with them. 他坚持要我同他们一起去。
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. 医生建议他不要抽烟。
He requires that I (should) appear. 他要求我出场。
注：(1) 其中引导宾语从句的that通常不省略。
(2) 这类句子有时可用于被动结构，前面用先行词it作主语，代表后面的从句：
It was proposed that this matter be discussed next time. 有人提议这事下次再讨论。
(3) 动词insist后接宾语从句时，除可用虚拟语气外，也可用陈述语气，两者的区别是：若谓语动词所表示的动作尚未发生，或尚未成为事实，则用虚拟语气；若谓语动词所表示的动作已经发生，或已经成为事实，则要用陈述语气。比较(www.yygrammar.com)：
He insisted that I had read his letter. 他坚持说我看过他的信。
He insisted that I should read his letter. 他坚持要我看他的信。
(4) 与动词insist相似，动词suggest后接宾语从句时，除可用虚拟语气外，也可用陈述语气，两者的区别也是：若谓语动词所表示的情况尚未成为事实，则用虚拟语气，此时suggest通常译为“建议”；若谓语动词所表示的情况为既成事实，则要用陈述语气，此时的suggest通常译为“表明”、“认为”。比较并体会：
He suggested that we (should) stay for dinner. 他建议我们留下吃饭。
What he said suggested that he was a cheat. 他说的话表明他是个骗子。
I suggested that you had a secret understanding with him. 我觉得你与他心照不宣。
(5) 以上动词用作名词或派生出的名词时，相应的主语从句、表语从句或同位语从句也用虚拟语气：
His demand is that we (should) set off at once. 他要求我们马上出发。
He made the demand that we (should) set off at once. 他要求我们马上出发。
(6) 在现代英语中，以上动词(包括其名词形式以及其派生名词)有时也可不用虚拟语气(但初学者宜慎用)：
Her suggestion was we had our conversation in French. 她的建议是我们用法语交谈。
He said that he would not be long and suggested that we waited for him. 他说他不会去很久，并建议我们等他。
7. 某些用虚拟语气的主语从句
形容词important, impossible, necessary等后的主语从句通常用虚拟语气：
It is impossible that he should go home. 他不可能会回家去。
It is necessary that I should return it right now. 我有必要马上还回去。
注：(1) 在现代英语中，有时也可不用虚拟虚拟语气而用陈述语气，但初学者宜慎用。
(2) 在It is amazing (strange, surprising, astonishing, a pity, a shame)以及 I am surprised (sorry) 和I regret等结构后的that 从句中有时也用should，表示说话人的惊异、懊悔、失望等情感，常含有“竟然”之意。如：
It’s strange that he should be so rude. 他竟如此无礼，真是奇怪。
I’m surprised that he should have failed. 他竟然失败了，这使我很吃惊。
若不用虚拟语气也可以，则不带感色彩，比较：
It’s a pity that he failed the exam. 他考试没及格，真是遗憾。
It’s a pity that he should have failed the exam. 他考试竟没及格，真是遗憾。
四、重点考点原创精练
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. _____.”(www.yygrammar.com)
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
参考答案：1―5 BABCA 6―10 BBCAC 11―15 ABADD