虚拟语气----高考重点难点
英语中虚拟语气是通过时态的变化来体现的。我们试图从句子时态的改变来推论出虚拟的构成。只要同学理解了这一点，就可以举一反三。掌握虚拟语气。
定义：虚拟语气是用来表示假设的，与事实相反或者不大可能实现的情况。主要通过动词时态的变化来体现。
规则：对于一个已经学过从句，又能正确使用时态的学生来说，掌握虚拟语气并不难。英语的虚拟语气是将句子动词原本应该使用的时态向后退一步，以表示该句与事实相反。后退的方法如下：
实际应用的时态------退------虚拟语气应用的时态
现在时--------退------过去时 do----did
现在完成时-----退-----过去完成时 have done-----had done
一般过去时----退----过去完成时 did----had done
一般将来时----退----过去将来时 will-----would
过去将来时----退----过去将来完成时 would-----would have done
情态动词 Can, may, shall------could, might, should
注：在虚拟语气中不用was,所有人称都用were.
虚拟语气在条件句中的应用：
1． If I have money, I will lend it to you. (主将从现)
If I had money, I would lend it to you.
第一句话没有使用虚拟，表示我很可能会借你钱。第二句话使用了虚拟，表示我不可能借你钱。用虚拟只是一种委婉的说法。对于两句的时态，正像我们上面所讲的，一般现在时退到一般过去时，一般将来时退到过去将来时。
2. If I have time, I will go to see you.
If I had time, I would go to see you.
请注意比较上面两句话不同的含义与时态的变化。
3. If I am you, I will buy that car. (假设句)
If I were you, I would buy that car.
由于我不可能是你，所以第一句话必须虚拟，因而第一句是错误的句子，但我们可以从中看出时态的变化。为了方便理解在下面的例句中都会给出一个假设句，但假设句只是为了逻辑说明。在实际应用中是不存在的，也就是错的。
4. 假设句：if it snows in summer, it will be great fun.
虚拟句：if it snowed in summer, it would be great fun.
如果夏天能下雪，那该多有意思。
从句：一般现在时---退---一般过去时 snows---snowed
主句：一般将来时---退---过去将来时will be ---would be
题：If there were no sun, the earth (would) not only be dark, it (would) also become extreme cold. 没有太阳是不可能的，所以是虚拟语气，对将来的虚拟退过去将来：will 退would.
5. 假设句：if I brought my checkbook yesterday, I would pay by check.
虚拟句： if I had brought my checkbook yesterday, I would have paid by check.
如果昨天我带支票来了，我就会付支票。（实际没付支票）
过去时-----退----过去完成时 Brought---- had brought
过去将来时---退----过去将来完成 would pay----would have paid
6. 假设句： if I had your address in New York, I would call on you before I came back to China.
虚拟句：if I had had your address in New York, I would have called on you before I came.
如果我有你在纽约的地址，我回中国以前，就去看你了。
从句：一般过去时----退----过去完成时 had---- had had
主句：过去将来时---退---过去将来完成时 would call on------ would have called on
题： I didn’t see your sister at the meeting, if she___, she would have met my brother.
A. Has come B. did come C. came D. had come
表示对过去时间的虚拟，过去时退过去完成时， 过去将来时退过去将来完成时。
7. 假设句：if you haven’t finished the homework by now, you will not be allowed to see the film this evening.
虚拟句：if you hadn’t finished the homework by now, you would not be allowed to see the film this evening.
如果你到现在还没做完作业的话晚上就不让你去看电影了。
从句：现在完成时-----退-----过去完成时 haven’t finished---hadn’t finished
主句：一般将来时----退-----过去将来时 will be allowed-----would be allowed
时间交错：错综句：
8. 假设句： if he took my advice, he will be a scientist.
虚拟句： if he had taken my advice, he would be a scientist.
如果他以前听我的建议，他将会成为一个科学家。
从句：过去时-----退-----过去完成时 took----had taken
主句：一般将来时----退-----过去将来时 will be----would be
9. 假设句：if you were there, the meeting might go smoothly.
虚拟句：if you had been there, the meeting might have gone smoothly.
如果你要是在，会就会开的更顺利。
从句：过去时---退---过去完成时 were------had been
主句：过去将来时----退----过去将来完成时 might-----might have gone
注：情态动词的时态倒退的方法与一般动词一样，如can, may等情态动词可以把他看做将来时，could, might看做过去将来时，could have done, might have done看做过去将来完成时。
10. 假设句：if there was more snow last year, we will have a good harvest this fall.
虚拟句：if there had been more snow last year, we would have a good harvest.
如果去年多下一点雪，今年秋天就会有个好收成。
从句：过去时---退----过去完成时 was----had been
主句：一般将来时---退---过去将来时 will have -----would have
虚拟条件句中if的省略：
如果虚拟条件句中有were, should或者had done,通常可将were, should或had 放在句首，if 可省略。
Eg: if I had studied more, I would have passed the test.
---- Had I studied more, I would have passed the test.
如果我多学习点，我就会通过考试。
If I were in your place, I wouldn’t say so.
----- Were I in your place, I wouldn’t say so. 如果我处在你的位置，我就不会这样说。
题：1. ____ for the free tickets, I would not have gone to the films so often.
A. If it is not B. were it not C. had it not been D. if they were not
虚拟条件句省略if条件句必须倒装，因条件句是过去时，所以应退过去完成时。 用介词短语表示虚拟条件：
11. 假设句：without your help, we will not be able to finish the work in time.
虚拟句：without your help, we would not be able to finish the work in time.
没有你的帮助我就不能按时完成这项工作。
一般将来时-----退-----过去将来时 will not be----would not be
12. 假设句：But for his good education, he would not get the job.
虚拟句：But for his good education, he would not have got the job.
幸亏他受过很好的教育，否则不会找到那份工作的。
过去将来时-----退-----过去将来完成时 would get-----would have got 在某些主语从句和条件状语从句中虚拟的用法：
在it is important, impossible, strange, vital, natural, essential, desirable, preferable, advisable, appropriate, surprising, sad that…..的句型中，主语从句在英国英语中用should+动词原形。在美国英语中省略should直接用原型。
在for fear that(以防….起见)引导的条件句中用法同上。
在unless, when, so (as) long as, suppose, in case, on condition 引导的条件状语从句中也可用虚拟语气，用法同上。
It is necessary that he (should) come on time to attend the meeting.
他按时来出席会议是必要的。
It is natural that he (should) love Mary. 他爱玛丽是很自然的事。
He took an umbrella for fear that it (should) rain.他带了一把伞，以防天下雨。
As long as my wife (should) get ready, we will go.只要我太太准备好了，我们就去。
注：在suggest, propose, demand, necessary, inquire, request, desire, insist, order, advise, agree等表示建议，要求，命令的动词后的宾语从句中，英国英语用should+动词原形，美国英语省略should用原型动词。
He insisted that we (should) get there on time. 他坚持我们要按时到那。
The dean proposed that the question (should) not be discussed at once.系主任提议这个问题不要马上讨论。
在think, expect, believe是否定形式时，宾语从句可用虚拟语气，should+动词原型， should不可省。
She said she never expected I should lend money to her.
Were (was) to 有时在虚拟条件句中用were (was) 表示试探的口气。
If you were (was) to do sth like that I would not marry you.
如果你要做那件事，我就不会嫁给你了。
Would have done, should have done上面两种用法也经常表示虚拟，意思是本应该做而没有做的事情。Would 表示从客观上讲，而should表示从主观上讲。
You would have taken taxi to come here. 你本应该坐出租车来这儿。(没坐车)
If I had known she was rich, I should have married her. 如果我知道她是个富翁，我本该娶她。（实际没娶她）
We ____last night, but we went to the concert instead.
A. Must have studied. B. might study. C. should have studied. D. would study
Should (would) have done 表示过去本该做，而没有做的事情。
重要提示：掌握虚拟语气，最好的方法就是记住在本该用的时态上向后退一步，即表示虚拟。现在时退过去时，将来时退过去将来时，过去时退过去完成时，过去将来时退过去将来完成时。这样，在虚拟语气中就不会再犯任何错误，即使遇上错综虚拟语气，也不会错。最后，记住几个特殊用法，虚拟语气就算基本掌握了。