虚拟语气: 虚拟语气在条件状语从句中的应用

时态：可以表示过去，现在和将来的情况。它的基本特点是时态退后。
a.　同现在事实相反的假设。
句型 ： 条件从句　　　　　主句
　　　　一般过去时　　　should( would) +动词原形
If they were here, they would help you.
If places _____ alike, there would be little need for geographers. 
A. being B. are C. be D. were 
如果各地方都一样，就不需要地理学家了。（Ｄ） 
b.　 表示于过去事实相反的假设。
句型： 条件从句　　　　　 主句　　　　　
　　　过去完成时　　　 should(would) have+ 过去分词
If she had worked harder, she would have succeeded.　　
The rice would not have been burnt if you had been more careful.　
If my lawyer had been here last Saturday, he would have prevented me from going.
If he had come yesterday, I should / would have told him about it.
含义：He did not come yesterday, so I did not tell him about it.
If he had not been ill and missed many classes, he would have made greater progress.
含义： He was ill and missed many lessons, so he did not make greater progress.　
If the policeman had arrived earlier, he would have seen the accident.
If better material had been used, the efficiency of the machine would have been much increased.
如果使用更好的材料，机器的效率会大大提高。
c.　 表示对将来的假想
　句型：　 条件从句　　　　　　 主句
　　　　 were+ 不定式　　　　 would + 动词原形
　　　　 should+ 动词原形
If you should succeed, everything would be all right.
If you were to succeed, everything would be all right.
If it should rain tomorrow, we should have to put off the picnic.
Jean doesn't want to work right away because she thinks that if she ____ a job, she probably wouldn't be able to see her friends very often. 
A) has to get B) were to get 
C) had got D) could have got 
吉不想立刻工作，因为她想：如果她得到一份工作，她就不能经常去看她的朋友了。(B)
2.2 混合条件句
主句与从句的动作发生在不同的时间，这时主，从句谓语动词的虚拟语气形式因时间不同而不同，这叫做混合条件句。
　　If you had asked him yesterday, you would know what to do now.
　 （从句与过去事实相反，主句与现在事实相反。）
　　If it had rained last night (过去), it would be very cold today (现在).
If I hadn't stood under the ladder to catch you when you fell , you ____ now. 
A) wouldn't be smiling B) couldn't have smiled 
C) won't smile D) didn't smile 
你掉下来的时候，如果我没有站在梯子下面看着你，你现在就不会笑了。 (A)
2.3 虚拟条件句的倒装
虚拟条件句的从句部分如果含有were, should, 或had, 可将if省略，再把were, should或had 移到从句句首，实行倒装。
Were they here now, they could help us. =If they were here now, they could help us.
Had you come earlier, you would have met him =If you had come earlier, you would have met him.　
Should it rain, the crops would be saved. =Were it to rain, the crops would be saved.

注意：
在虚拟语气的从句中，动词'be'的过去时态一律用"were"，不用was， 即在从句中be用were代替。
If I were you, I would go to look for him. 如果我是你，就会去找他。
If he were here, everything would be all right. 如果他在这儿，一切都会好的。
_____ to do the work, I should do it some other day.
A. If were I　　 B. I were　C. Were I　D. Was I
答案C. 在虚拟条件状语中如果有were, should, had这三个词，通常将if省略，主语提前, 变成 were, should, had +主语的形式。但要注意，在虚拟条件状语从句中，省略连词的倒装形式的句首不能用动词的缩略形式。如我们可说 Were I not to do., 而不能说 Weren't I to do.
练习
My cat wouldn't have bitten the toy fish _____ it was made of rubber. 
A) if she has known B) if she knew 
C) she should have know D) had she known 
如果我那只猫知道那条玩具鱼是用橡胶制作的，她就不会去咬它了。 (D）
____ for my illness I would have lent him a helping hand. 
A) Not being B) Had it not been 
C. Without being D) Not having been 
如果不是我病了,我本来是会帮助他的。（B) 
____ before we depart the day after tomorrow, we should have a wonderful dinner party. 
A) Had they arrived B) Would they arrive 
C) Were they arriving D) Were they to arrive 
如果我们后天走之前他们到达的话，我们就举行一次丰盛的宴会。 (D） 
____ right now, she would get there on Sunday. 
A) Would she leave B) If she leave 
C) Were she to leave C) If she had left 
如果她立刻就走,她就能在星期天到达那里。(C) 
Had he worked harder, he ____ the exams. 
A) must have got through B) would have got through 
C) would get
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