虚拟语气表示说话人的愿望、假设、猜测或建议，而不表示客观存在的事实。虚拟语气通过谓语动词的特殊形式来表示，对虚拟语气在各种句式中的用法介绍如下：
A).条件从句的虚拟语气
条件从句的谓语动词 主句的谓语动词
与现在事实相反 be---were/ 动词---过去式 would/ should/ might/ could + do
与过去事实相反 过去完成式 would/ should/ might/ could + have done
与将来事实相反 were to/ should + do/
动词---过去式 would/ should/ might/ could + do
Eg. 如果我是你，我就不看电视了.
If I were you, I should/would not watch TV.
如果我做完家庭作业，我就去参加晚会.
If I did/had done my homework, I would go/have gone to the party.
如果你昨天晚上不看电视，就不会迟到了.
If you hadn’t gone to the cinema, you would not have been late for class.
如果你努力地学习的话，你就会考试及格了。
If you had studied harder, you would have passed the exam.
The plants in our garden __________ better if it had not rained so much last year.
A. had grown B. would have grown C. were growing D. would grow
Note:
a).条件从句中if 的省略，要倒装
如果条件从句的谓语动词包含有were或助动词、情态动词had, should, could，有时可将连词if省去，而将 条件从句的主语置于were, had, should, could之后。这种用法主要用于书面语，如：
a.与现在相反：If I were you (=Were I you) , I would go with him.
b.与过去相反：If I had had time then (=Had I had time then), I would have gone with you.
c.与将来相反：If I were to visit/should visit/visited the Great Wall tomorrow, (=Were I to /Should I visit the Great Wall tomorrow), I would take my son with me.
注意：在否定句中not不可提至主语前，如：
（误）Weren’t I here now, I would be in the bus.
（正）Were I not here now, I would be in the bus.
b).without 可以代替条件从句
Eg.没有水和空气，我们就不能生存。
We would not live without water or air.
c) 混合虚拟条件句
如果条件从句的动作和主句的动作不是同时发生，主句和从句的谓语动词的形式应分别根据各自所表示的 时间加以调整。这种句子叫做混合虚拟条件句。如：
If he had followed my advice, he would be quite all right now.（从句述说过去，主句述说现在）
IfChinahad not been liberated, the working people would still be leading a miserable life.（ 从句表示与过去的事实相反，主句说明与现在的事实相反）
d) 省略主句，只保留if(only)的条件句
虚拟条件句中的表示结果的主句有时形式上可以省略，但意义仍然存在。这
种句子只保留一个if(only)条 件从句，表达说话人的强烈愿望。如：If(only)she
were my sister！她是我的妹妹就好了！
e) 用but或but for引导含蓄条件句（but后跟从句，but for后跟短语: 假如没有, 要不是）
But for your help, our experiment wouldn’t have been so successful.
假如没有你们的帮助，我们的实验是不会如此成功的。
But for the storm, we should have arrived earlier.
要不是碰到暴雨我们会到得早一些。
We would have invited them to the dance, but they were too busy.
要不是他们太忙，我们会邀请他们来参加舞会的。
此句可改写为：If they had not been so busy, we would have invited them to the dance.
But that he is in hospital, He would go abroad for his summer vacation.
要不是生病住院，他就出国度暑假了。
该句可改写为：If he weren’t in hospital, he would go abroad for his summer vacation.
f) "If only ..."这是一种特殊句式结构
一、"If only..."用于感叹句中,是一个保留条件句,省略了主句的形式。用来表示某人对某事的一种强烈愿望或未实现的条件,其意为"但愿……;真希望……;要是……就好了"。常用于虚拟语气的谓语动词形式。
If only she were my sister! 如果她是我姐姐该多好啊!
(=How fine it would be if she were my sister!)
"If only..."引导的从句谓语动词形式分以下几种:
1. If only后常接一般过去时,表示对现在的一种难以实现的愿望。
如:1)If only I had that book! 我要是有那本书就好了。
=How fine it would be if only I had the book (but I haven't the book).
2)If only I were younger! 要是我年轻点儿就好了!
=How fine it would be if only I were younger! (but I am not younger)
3)If only my mother were here now! 要是我母亲现在在这儿就好了。
(but she isn't here now)
4)How fine it would be if only they could find a way to get to the room!他们要是能够找到一条通道进入那个房间该多好啊!
2. If only后常接过去完成时,表示过去没有实现的愿望。
如:1) If only you had worked with greater care! 你当时干活时要是再认真些就好了!
(but you didn't work with greater care)
2) If only we had arrived in time, we would not have missed the train! 要是我们及时赶到,就不
会误车了。(but we didn't arrive in time)
3. If only后常用过去将来时表示将来不大可能实现的愿望。
如:If only she would win!但愿她能赢!
二、If only有时也可引导陈述语气的真实条件句,意思为"只要……"。
If only it clears up, we'll go. 只要天一放晴,我们就去。
与此句型容易混淆的还有一种结构"only if...",only置于if前表示强调if条件,意为"只要……",用于引导陈述语气的真实条件句。
Only if you study hard, you will pass the test. 只要你努力学习,就会通过考试。
B).宾语从句的虚拟语气
a).wish+宾语从句 与现在/将来事实相反 谓语动词--- be---were/ 动词---过去式
与过去事实相反 过去完成式
eg. I wish I were a bird flying freely in the sky.
I wish you passed the entrance exam.
I wish you hadn’t been absent yesterday.
b).表示请求，命令，建议的动词后(一坚持(insist),二命令(order, command),三建议(suggest, propose, advise),四要求(demand, require, request, ask)
谓语动词---(should)+do
eg.我们建议她去看医生。
We suggested that she (should) go to see a doctor.
例外情况：suggestion，insist后从句中不用虚拟语气的问题．
suggest作为“表明，暗示”时，不用虚拟语气
insist作为“坚持认为”时，不用虚拟语气
eg. The smile on his face suggested that he succeeded in the task.
我们坚持他应该去看医生。(坚持要sb做)
We insisted that he (should) go to see a doctor.
We insisted that old Li was an advanced worker in our company.
Jane's pale face suggested that she ______ ill and her parents suggested that she ______ a medical examination.
A. be; should have B. was; have C. should be; had D. was; has
C).主语从句的虚拟语气
It is important/necessary/strange + that+主+(should) do.
Eg. It is necessary that we (should) master a foreign language to find a good job.
D).状语从句的虚拟语气
a).方式从句 与现在/将来事实相反 谓语动词--- be---were/ 动词---过去式
与过去事实相反 谓语动词---过去完成式
eg.她很悲伤仿佛整个世界都背叛了她。
She felt upset and sad as if/as though the whole world had turned against her.
b).让步从句 与现在/将来事实相反 谓语动词--- be---were/ 动词---过去式
与过去事实相反 谓语动词--- 过去完成式
eg.即使他向我道歉，我也不会原谅他。
Even if/Even though he apologized to me, I wouldn’t pardon him.
E).it is (high, about) time+从句的虚拟语气从句应该用虚拟语气，值得注意的是
1.用过去时态表示虚拟．
Or 2.should + 动词原形，should 不能省．常译为＂是（正是）．．．的时侯．．．＂
It is (high, about) time for + sth.
It is (high, about) time for sb to do.
