虚拟语气在从句中的用法
1. 主语从句中的用法
(1) 在以it为形式主语的复合句中，虚拟语气在主语从句中表示建议、要求、命令等，谓语动词用should be型或be型虚拟式，在美国英语中常用be型虚拟式。如：
It's natural that she should do so.
她这么做是很自然的事。
It is essential that we should tell her the news.
我们有必要告诉她这个消息。
It is important that we should make full use of our mineral resources.
对我们来说，充分利用我国的矿产资源是重要的。
It is strange that the result of the experiment should be unsatisfactory.
奇怪的是实验结果竟然如此令人不满意。
It is desired that we should get everything ready by tonight.
希望一切在今晚准备好。
It was arranged that Mr Sam should go and help Bettie.
他们作了安排，由萨姆先生去帮助贝蒂。
(2) 主句的谓语为某些动词的被动语态，常用在It is (was) desired (suggested，settled，proposed， recommended，requested，decided，etc.) that...句型中。
It is suggested that the question should be discussed at the next meeting.
有人建议在下次会上讨论这个问题。
It is vital that he should be warned before it is too late.
在还不太晚的时候警告他是非常必要的。
It has been decided that the sports meet should be postponed till next Friday.
已决定运动会延期到下星期五。
It was requested that a vote (should) be taken.
有人要求进行表决。
2. 在宾语从句中的用法
(1) wish的宾语从句中的谓语动词形式
① 动词的过去式表示对现在情况的假设。如：
I wish prices would come down.
我真希望物价会下降。
I wish you would stop asking silly questions.
我希望你不要再问这种愚蠢的问题。
I wish I knew his address.
可惜我不知道他的地址。
I wish we could go with him.
我们要是能跟他一起去该多好。
② had+过去分词表示对过去情况的假设。如：
I wish I had known it before.
我真希望我预先知道这件事。
He wishes he hadn't been rude to his parents.
他真希望他没有对父母无礼。
She wished that she had stayed at home.
她想那时要是留在家里就好了。
I wish I could have been there yesterday.
要是我昨天到过那里该多好。
(2) would rather等的宾语从句中的谓语动词形式
用would rather(=would sooner)和would(just)as soon(=would sooner)等表示愿望，但其宾语从句常用虚拟过去式。如：
I would rather you came tomorrow than today.
我宁愿你明天来，而不是今天。
I could do it myself but I would sooner you did it.
我自己也可以做，但我宁愿你去做。
I would rather you had told me the truth.
我倒想你本该把事实真相告诉我。
(3) suggest等的宾语从句中的谓语动词形式
① 用should＋ 动词原形或只用动词原形的that 从句，作为 demand, order, propose, request, require, suggest, arrange, insist, command, desire, advocate, maintain, urge, direct, move, prefer, arrange, recommend 等词的宾语。如：
The expert proposed that TV should be turned off at least one four every day.
专家提议每天至少应该关掉电视一个小时。
The board recommended that the company should invest in the new property.
董事会建议公司投资新的房地产。
The committee has given instructions that the manager should fly to New York.
委员会已发出指示，要经理飞往纽约。
Secretary of War Edwin M. Stanton ordered that James Van Metre should be released.
陆军部长埃德温·Ｍ·斯坦顿命令将詹姆斯·范·米特释放。
He asked that the arrangements be made to help them finish the work.
他要求做好安排，帮他们完成工作。
Experiments demand that accurate measurements be made.
实验要求做到准确的计量。
She insisted that we take up the matter at the meeting.
她坚持要求我们在会上谈这个问题。
② 有些动词，如think, expect, believe 其否定式的宾语从句亦可用should ＋ 动词原形。如：
I never thought he should refuse.
我万没想到他会拒绝。
I had not expected that things should turn out like this.
我没料到事情的结果竟是这样。
3. 在表语从句中的用法
虚拟语气也可用在表语从句中。这种从句由that（可省略）所引导，其谓语是 should ＋动词原形。句子主句中的主语常常是suggestion, proposal, idea, motion, order, recommendations, plan, impossibility, possibility等名词。如：
His suggestion was that everyone should have map.
他的建议是每人发一张地图。
My idea is that the electronic device should be tested at once.
我的意见是这一电子器件要立即试验。
在主句中作主语的名词常见的有： advice， aim， desire， idea， insistence， motion， necessity， order， plan， proposal， recommendation， regulation，requirement， suggestion， wish等。
4. 虚拟语气在同位语从句中的用法
当与同位语从句同位的是suggestion等表示建议、计划、命令等的名词时，从句的谓语动词用should+动词原形，美国英语中常用动词原形。
They made the request that the problem should be discussed as soon as possible.
他们要求尽快讨论这个问题。
He gave orders that the work should be started at once.
他命令工作马上开始。
The proposal that he (should) be dismissed was supported at the meeting.
大会对开除他的提议表示了支持。
5. 虚拟语气在状语从句中的用法
(1) 虚拟语气在让步状语从句中的用法
① 由连接词whether, if, even if/though, whatever, so long as 引导的状语从句，其谓语可用虚拟语气，即其谓语用动词原形。如：
Whether the figures be accurate or not, they have to be rechecked.
不管那些数字准确与否，都得重新核对。
The earth is powerful magnet and all magnets behave the same whether they be large or small.
地球是一个强大的磁体，而所有的磁体无论大小其作用都是一样的。
They have decided to build a reservoir, whatever the difficulties may be.
他们决心建造一座水库，不管有多少困难。
I won't let you in whoever you may be.
无论你是谁我都不让进去。
However hard the task may be, we must fulfill it on time.
不管任务多么艰巨，我们必须按时完成。
If the defendant be found guilty, he shall have the right of appeal.
如果被告被判有罪，他有权上诉。
② 倒装的让步状语从句中的虚拟语气。如：
Come what may，we will go ahead.
不管怎样，我们一定要前进。
However hard it may rain，we shall have to go.
无论雨多大，我们都得走。
(2) 虚拟语气在方式状语从句中的用法
以连接词as if引导的状语从句（谓语形式与wish后的宾语从句相同，be在第一、三人称可用was或were）。如：
You speak as if you had really been there.
你说的好像你真的去过那里。
Light often behaves as though it were made of particles.
光的性状，常常有点儿像由粒子组成的。
He spoke to me as if I was(were)deaf.
他跟我说话时就好像我是聋子似的。
(3) 虚拟语气在目的状语从句中的用法
以 lest, for fear that 和 in case 引出的状语从句（谓语多用 should 加动词原形构成）。如：
Batteries should be kept in dry places lest electricity should leak away.
电池应放在干燥的地方，以免漏电。
He handled the instrument with care for fear that it should be damaged.
他小心地弄那仪器，生怕把它弄坏。
I'll keep a seat for you in case you should change your mind.
我给你留一个位子，说不定你会改变主意。
6. 虚拟语气在it is time后的定语从句中的用法
虚拟语气还可用在定语从句中，这种从句常用在it is (high, about) time (that)．．．句型中。定语从句常用虚拟过去式。如：
It is time we started.
我们该出发了。
It is time we set to work.
我们该着手工作了。
It is time we left.
我们该走了。
It is time we should leave.
我们该走了。
It is time I were off.
我该走了。
It's high time the weather improved.
天气真该好起来了。
但要注意：位于time之前的high起着强调“为时稍晚”的作用。