关于虚拟语气的详解
在英文句子中，谓语动词的语气是用来表示说话人对所讲内容的态度、看法以及心情等。
英文句子中谓语动词的语气有三种：
A）直陈语气（The Indicative Mood）直陈语气用于直截了当地陈述事实、描述状态：
He has published quite a number of essays this year .他今年已发表了好几篇论文。
B) 祁使语气（The Imperative Mood）
祁使语气用于提出请求、命令、建议或是劝告等：
Wait outside until you are asked . 请在外面等候，请你进再进去。
Let''s just take a break, shall we ? 我们休息一会儿，好吗？
C) 虚拟语气（The Subjunctive Mood）
虚拟语气用于表示主观愿望和假设的虚拟情况。虚拟语气不太顾及事实的存在，它表现出说话人的主观因素比较多。所以说话人所讲的内容往往是与事实相反的；或是其实现的可能性微乎其微，甚至于没有实现的可能性。当然，有时为了使说话的语气客气、缓和、委婉，也使用虚拟语气。例如：
I wish you were more careful .但愿你更细心一些。
If I had more money, I would buy a bigger apartment.
我要是有再多一点钱，我就买一套更大一些房子。
Would you mind shutting the door ? 劳驾您把门关上。
用于非真实条件句中的虚拟语气
条件句分为两种：真实条件句和非真实条件句。
与现在事实相违背
If I had time, I would certainly join you in the tennis match. （事实是：我没有时间）我要是有时间肯定和你一起打这场网球比赛。
If I were you, I would put her suggestion into account.（事实是：我并不是你）我要是你，我会考虑她的建议的。
与过去事实相违背
If I hadn''t been caught by something, I would have come to your party yesterday.(事实是：我昨天被某些事缠住了)
我昨天要不是被些事缠住了，我就会去参加你们的聚会了。
If he had taken my advice, he might not have made such a bad mistake.
（事实是：他没有听我的建议）要是他听进了我的劝告就不会犯这么严重的错误了。
与未来事实相违背
If I should have a chance to try it, I would do it in another way.
（假设的情况不大可能发生）要是我有机会试一试，我会用另一种方法做的。
Even if they were to fail, they wouldn''t lose courage.
（说话人不希望假设的情况发生）即使他们万一失败，他们也不会泄气。
熟悉并掌握好下面的基本句式：
条件从句 主句
与现在事实相违背 过去式（动词是BE用were） Should / would + 动词原形
与过去事实相违背 had + 过去分词 would / should + have +过去分词
与未来事实相违背 1) should + 动词原形
2) were + 动词不定式
3) 过去式（动词是BE也可以用were） would / Should + 动词原形
1. 省略If的几种情况
1）当条件状语从句的谓语部分含有had、should、或were时，就将这样的词had、should、或were搬到句首把句子写成倒装句而将连词if省略。例如：
If you were the manager here, what would you do?
Were you the manager here, what would you do? 你若是这里的经理，你会怎么办？
If he should act like that again, he would be fired immediately.
Should he act like that again, he would be fired immediately. 要是他再那样做，他会被立即解雇的。
2) 由某些介词短语取代了if引导的条件状语从句。例如：
Without air, there would be no life on the earth. 要是没有空气，地球上就不会有生命了。
But for your help, the little boy would have been drowned. 要是没有你们的帮助，那个小男孩早就淹死了。
We could have done the work better in that case. 要是那样的话，我们本可以把工作干得更好一些的。
3) 由上下文的交代而省略了if引导的条件状语从句。在这种情况下，上下文事实上就是一个表示违背事实的条件句。上下文如果是由一个句子介绍的，那么这个取代了if条件状语从句的句子应该用直陈语气；而起主句作用的句子则要用虚拟语气。例如：
He would have come to see you earlier but he just came back from his business trip .（本句中的上下文是：but he just came back from his business trip，表示：要是他在家没出差的话）他本来早就来看你了，可他却出差刚刚回来。
But that you helped me, I would have failed in the experiment. （本句中的上下文是：But that you helped me，表示：要不是有你帮助我）要没有你帮助我，我的试验本做不成功的。
2. 虚拟语气用于某些从句中的情况：
1）在主语从句中
在It + be +形容词/ 名词 + that从句的结构中，由于某些形容词/ 名词的原因，that从句中的谓语动词要用虚拟式"should + 动词原形"或是"动词原形"。
这类形容词/ 名词常见的有：essential（绝对必要的）, important（重要的）, advisable（明智的）, desirable（希望能够的）, imperative（必须的）, natural（自然的）, necessary必要的）, regretful（遗憾的）, strange（奇怪的）, proper（适当的）, urgent（紧急的）, duty（义务、责任）, a pity（遗憾）, no wonder（难怪）, a regret（遗憾）, 例如：
It is strange that he ( should ) say so .他居然会这样说，真是奇怪。
It is a great pity that you ( should ) think so . 他居然会这样想，真是一件憾事。
It is natural that a bird ( should ) rest in trees . 鸟在树上安歇是很自然的。
It is necessary that he be sent to Beijing right away. 有必要立即派他去北京。
另外，下列结构中主语从句的谓语动词也要求用虚拟语气：
It is ordered that …(根据命令、要求……) ,
It is proposed that …(人们建议……)
It is desired that … (最好、需要……) ,
It is requested that … (人们要求……)
It is suggested that … (有人建议……) ,
It is recommended that …(有人推荐……)
It is demanded that …(根据要求……) ,
It is decided that …(已经决定……)
It is arranged that … (已经安排……) 等等。例如：
It is ordered that all the troops (should) withdraw three miles away.
根据命令，所有部队撤至三英哩以外。
It is arranged that he leave for Canada on Friday.
照安排，他星期五动身去加拿大。
It is suggested that the English evening be held on Saturday.
有人建议，英语晚会周六举行。
