定语从句与虚拟语气
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㈠虚拟语气在条件句中的应用：
英语中if 从句有两种：一种是以述语气叙述的叫做真实条件句，说明所提出的假想是可以实现的；另一种是以虚拟语气叙述的，叫非真实条件句，说明所提出的假想实现的可能性极小或与事实相反。这种虚拟语气一般因所指的时间的不同而分三种情况：
⒈ 表示与现在事实相反：
If + 从句主语 + 动词的过去式…，主语+should/ would/ could/ might + 动词原形…
（be 一般用were）
如：
①If I were you, I would go by plane.
如果我是你，我将坐飞机去。（ In fact I am not you. ）
②If he were here, he would decide what to do.
如果他在这里，他会决定做什么。（In fact he isn’t here.）
③If I had the letter at hand, I would read it.
如果我手头有这封信的话，我会读它的。（In fact I don’t have the letter at hand.）
④If she knew about it now, she would come.
如果她现在要是知道这件事的话，她会来的。（In fact she doesn’t know about it.）
⑤If he had time, he would go with you.
如果他有时间，他会同你一起去的。（In fact he is very busy, so he can’t go with you.）
⒉ 表示与过去事实相反：
If + 从句主语 + had + 过去分词…，主语+should/ would/ could/ might +have +过去分词…
如：
①If he had come here yesterday, I should have told him.
如果他昨天到这里来，我早就告诉他了。
(Fact: He did not come and I did not tell him.)
②If I had taken his advice, I wouldn’t have made such a mistake.
如果我当时接受了他的劝告，我是不会犯那样一个错误的。
(Fact: I didn’t take his advice and I made such a mistake.)
③If I hadn’t been so busy last Monday, I would have called her.
如果我上周一不忙的话，我早就给她打了。
(Fact: I was busy last Monday and I didn’t cal l her.)
⒊与将来事实可能相反：
①动词的过去式…，
If + 从句主语+ ②should +动词原形…， + 主语 + should/ would/ could/ might + 动词原形…
③were to +动词原形…，
如：
①If it should snow/snowed/were to snow tomorrow, I would not go out.
如果明天下雪的话，我就不出去了。
(But I know it won’t snow tomorrow.）
②If he failed/should fail/were to fail, he would try again.
如果他失败的话，他会再试一次。
(I know that most probably he won’t fail.）
③If I had time next year, I would study German.
如果我明年有时间的话，我就学德语。
(I know that most probably I won’t have time next year.)
◆ 在书面语中，有时if虚拟从句可使用倒装形式，方法是：如果if从句中含有were, had 或should时，把条件从句中的if省略，将were/ should/ had 移至主语之前。
如：
①If I were in his place, I should learn to drive.
→ Were I in his place, I should learn to driv e.
如果我处于他的地位，我一定学开车。
②If it should snow tomorrow, the meeting would be put off.
→ Should it snow tomorrow, the meeting would be put off.
如果明天下雪，会议将会延期。
③If they had helped us, we would have succeeded.
→ Had they helped us, we would have succe eded.
如果他们帮助了我们，我们早就成功了。
④If it were to snow tomorrow, what would you do?
→ Were it to snow tomorrow, what would you do?
万一明天下雪的话，你怎么办。
◆ 如果从句和主句所表示的动作发生的时间不一致，例如：一个与过去事实相反，另一个与现在事实相反，动词的虚拟语气形式应根据所指的实际时间来选用。
如：
①If he were alive, he might h ave finished his scientific researches on the bridge-building three years ago.
如果他现在还活着，他可能三年前就完成了他的桥梁建筑科研工作了。
（从句所表示的动作与现在事实相反，主句所表示的动作与过去事实相反）
②If you had followed his advice, you would not be in trouble now.
如果你当初听从他的建议，你现在就不会陷入这种困境了。
（从句表示的动作与过去相反，主句所表示的动作与现在相反）
③If I had followed the doctor’s advice, I would be quite all right now.
如果我当时听从了医生的建议，我现在就完全恢复了健康。
（从句所表示的动作与过去相反，主句所表示的动作与现在相反）
④If I were you, I would have gone with her.
如果我是你，我早就和她一起去了。
（从句表示与现在事实相反，主句所表示的动作与过去事实相反）
◆ 有时假设的情况并不以条件从句表示出来，而是通过一个介词短语来表示
如：
①We could have done better under more favourable conditions.
在更有利的条件下，我们还可以做得更好些。
②Without the warmth and light of the sun, the earth’s vegetation would die almost immediately.
如果没有太阳的热量和光，地球上的植物几乎会马上死去。
◆ 假设的情况有时可以通过上下文或其他方式来表现：
如：
①I was ill that day. Otherwise I would have taken part in the sports meet.
我那天生病了，否则就参加运动会了。
②But for the storm, we should have arrived earlier.
要是没有碰到暴风雨，我们还会早一些到的。
③I would have written before, but I have bee n ill.
本来该早就给你写信的，但我生病了。
㈡虚拟语气在wish后的宾语从句中的应用：
wish 的各种时态都不影响从句的时态
⒈ 与现在事实相反的愿望：
wish + 从句主语+ 动词的过去式
如：
①He wishes he were a bird.
他希望自己是一只小鸟。
②I wish I were ten years younger.
真希望自己年轻十岁。
③I wish I remembered the address.
我要是记得地址就好了。
⒉ 与过去事实相反的愿望：
wish + 从句主语+ had + 动词的过去分词
如：
①She wished she had been braver then.
她真希望那时她胆子大一些。
②I wish he had gone to the exhibition.
要是他去参观展览会就好了。
③I wish you had been here yesterday.
要是你昨天在这里就好了。
④We wish we had paid more a ttention to our pronunciation.
但愿我们过去对发音注意得更多一些。
⒊ 与将来事实可能相反的愿望：
wish + 从句主语+ should/would/could/might + 动词原形
如：
①We wish that he could be with us tomorrow.
但愿他明天和我们在一起。
②I wish he would try again.
我希望他还能再试一次。
㈢虚拟语气在suggest, demand, propose, command, request, desire, order, insist等动词之后的宾语从句中，表示命令和建议：
suggest/ demand/ propose/ command/ request/ desire/ order/