情态动词的用法can/could/may/might/will/would/shall/should/must/can'

情态动词的用法
can/could/may/might/will/would/shall/should/must/can't的用法,分着说.

can , could 能,会
（could可以看作是can的过去式,这两个词除了时态不相同外,在表达意思的许多方面是相同的.当然could也有自己独特的用法.）
1）表示脑力或体力上的能力
Nobody can stop the development of science .
谁也无法阻止科学的发展.
She can sing that song in English.她能用英文唱那歌.
He can submerge to a depth of about twenty meters .
他能潜入约二十米深的水中.
He could hardly support his family before he found the new job .他在找到那份新工作前几乎无 法养家.
I could not understand the lecture on the computer given by Mr. Smith .
我听不懂史密斯先生作的那个关于计算机的讲座.
2)表示客观上的可能性
You can borrow this useful book from the library .
你可以从图书馆借到这种有用的书.
A more suitable person than him for the job can not be found . 不可能找到比他更适合这份工作的人了.
Now people can skate on the lake .现在人们可以在湖上滑冰了.
When the storm stopped , the plane could take off .
当风暴停下来时,飞机可以起飞了不得.
3)表示主观上的允许
Can I ask you some questions about it ?
我可以问你有关这件事的几个问题吗?
You can not leave here till I come back .直到我回来你才能离开.
Such kind of thing can't happen any more later .
这类事以后不准再发生了.
Can you tell me how to get to the airport ? 你能告诉我怎么去机场吗?
Could you tell me how to get to the airport ?
您能告诉我怎么去机场吗?
Could I be forgiven my negligence ? 请原谅我的疏忽,行吗?
4）（用于否定句、疑问句或感叹句中）表示猜测、怀疑或惊诧
How can / could you be here ? 你怎么会在这儿?
She couldn't / can't be so stupid to do that .
她不可能蠢得去做那种事吧.
He couldn't / can't be over seventy .他不可能有七十多岁了.
Where could / can the boy be now ? 那孩子现在能在哪儿呢?
另外,could还常用于表示较客气委婉的看法、提问及用于虚拟语气的结构中.这时候,could就不可以看作是can的过去式了.而是could自己独特的用法.如：
Could you speak a little slowly ?
您能稍微说慢一点儿吗?
I'm afraid that we couldn't give you any definite answer at this moment .
恐怕我们这时候还无法给予您任何确切的答复.
I could come earlier if asked .
如果要让我早一点来,我可以来早一点.
We would appreciate it if you could offer us any help .
如果您能为我们提供帮助的话,我们将不甚感激.
You could have done better if you had worked harder at it .
如果你再加把劲,本来可以干得更好一些的.

may , might 或许,可能,可以
（might可以看作是may的过去式,这两个词除了时态不相同外,在表达意思的许多方面是相近的.当然may 和might又都有一些各自不同的独特用法.）
1）可能性
I may be busy from tomorrow on .从明天起我可能会忙起来.
You may catch sight of the sunrise from here when you get up before 5 in the morning .你在早晨五点钟以前起来,或许能从这儿看到日出.
I wondered if they might agree with the idea .我想知道他们是否会同意这种想法.
She thought it might be wise to try her luck here .
她认为在这儿碰碰运气也不错.
2）表示允许
May I come in ? 我可以进来吗?
I'd like to have a smoke here if I may .
如果可以的话我想在这儿抽一支烟.
The librarian told her that she might return the book to the library in three days .
图书馆理员告诉她说,她可以在三天后还那本书.
At the press conference , a news reporter asked the chairman if she might trouble him with a question about Taiwan issue.
在记者招待会上,一位新闻记者问大会主席她是否能提一个有关台湾问题方面的问题.
3) may间或用来表示祝愿,也常用于表示目的或让步的状语从句中:
May that day come soon .但愿这天早日到来.
May you succeed in winning the first prize in the game .
祝愿你比赛夺冠成功.
May you continue in your efforts and achieve greatersuccesses .
祝愿你继续努力并取得更大的成功.
4) might也常用于表示目的等状语从句中,或用于虚拟语气的结构中:
I could not convince him , try as I might .我无论用什么样的办法也不能说服他.
They left off earlier on that day so that they might catch the first train .
那天,他们为了赶上头班车动身早一些.
He died so that the others might live .
为了其他的人能活下去,他自己牺牲了.
If you had made better use of your time , you might have learned more .假若你将自己的时间利用得更好一些,你本可以学到更多东西的.
One error in calculation might ruin the whole project .
计算中出一点错就可能毁掉整个工程.
注意：在回答以may引导的问句时,一般说来避免使用may,以免显得太严厉、或不太客气,而改用其他方式.例如：
--May I come in ? --Yes , please .请进.
我可以进来吗? --Sure . / Certainly . .请进.
--Please don't . .请不要进来.
--No , you mustn't .不行.
must 应该,必须,一定
1) 表示出于职责、义务该做某事
We must protect people's rights .我们应该保护人民的利益.
Everyone must be loyal to his motherland .
每个人都应该忠于自己的祖国.
You must serve the people when you grow up .
你们长大成人时应该服务于人民.
Students must work hard at their study .
学生应该努力学习.
2）表示出于主观意识而必须要做某事
We must speed up the pace of our economic reform .
我们必须加速经济改革的步伐.
We must keep steps to the scientific development .
我们一定要与科学的发展保持一致步调.
You must hurry up or you'll be late .
你必须得快点儿,不然会迟到的.
在这种用法中must表示出于主观意识而必须要做某事；have to却表示由于某种客观原因而不得不做某事.除此以外,have to自身有时态的变化形式.如：
I have to go now for I've got a meeting 15 minutes later.我现在必须要走了,因为我15分钟后有个会要开.
He has to be back home by five to fetch his son from kindergarten .
他必须在五点钟前回家去幼儿园接他的儿子.
Jenny had to tidy up the room before her mother came back .
珍尼不得不在她妈妈回家以前将房间整理好.
We'll have to reconsider the whole thing .
我们将不得不重新考虑整个事情.
注意：在这种用法中,回答以must引导的问句时,若是否定答复,不可以用mustn't 而需要用needn't 或是don't have to,因为mustn't意思是"绝不能、一定不要",而没有"不必"的意思.例如：
--Must we hand in our exercises today ? 我们今天必须交作业吗?
--Yes , you must .是的,必须交.
--No , you needn't (or , you don't have to ).
不,不必今天交.
3）表示禁止（用于否定句）
You must not speak ill of others .
你一定不要说别人的坏话.
Cars must not parked here . 这里禁止停车.
Smoking must not allowed in the office .严禁在办公室吸烟.
You mustn't talk to girls like that .你绝不能那样对女孩子说话.
4）表示猜测、推测must常用于肯定句中表示猜测.对现在或未来的事进行猜测时,后接动词原形；对已经发生的事进行猜测时,后接have + 过去分词.例如：
You must be tired after working so long .你工作这么久以后,肯定累了吧.
It must be that naughty boy crying outside .肯定是那个调皮的孩子在外面大叫.
The idea must be accepted by the society sooner or later.
这种想法肯定或迟或早会被社会所接受的.
It must have rained last night for it is so wet outside .
外面这么湿,昨晚肯定下雨了.
I didn't see you in class yesterday. You must have been
absent .我昨天上课没见着你,你肯定没有来.
Ought （后接带to的不定式构成谓语动词）应该
1）表示出于职责、义务该做某事
You ought not to be so careless in your work .你不应该在工作上如此粗心大意.
We ought to study hard for the sake of our motherland.
我们应该为了我们的祖国而努力学习.
His doctor said to him that he oughtn't to smoke so much .
他的大夫说他不应该抽这么多烟.
Oughtn't you to give us a chance to try ?
你难道不应该给我们一个尝试的机会吗?
2) 表示极有可能发生某事
As an auto repairman , Dick ought to know what is wrong with the car .
狄克作为一个汽车修理工总该知道这部车的毛病所在吧.
If we set off right now , we ought to be able to get there in time .
如果我们马上出发,我们应当能够按时到达那里.
Tomorrow ought to be a nice day for we have such a fine sunset today .
今天有这么好的晚霞,明天准是个晴天.
need（用于否定句和疑问句）需要
There are still one and a half hours to go , we needn't be insuch a hurry .
还有一个半小时,我们无需如此慌慌张张.
I hardly need say how much we missed you .不用说我们是多么想念你啊.
Need you go so soon ?你需要这么早就去吗?
You need have no anxiety on my account .你不必为我而着急.
dare , dared（用于否定句、疑问句和疑问句）敢
Dare you stay here alone in the night ? 你敢在夜里呆在这儿吗?
Nobody dared mention that matter. 没有人敢提那件事.
How dared you say that to her ? 你怎么敢对她说那件事?
Even if you dare do it , I won't allow you to because it's too dangerous .
即使你敢做,我也会让你做那件事,因为太危险了
shall 用作情态动词时,适用于第二人称和第三人称.
主要表示下面几层意思：
1）许诺
You shall hear everything directly you come .你一来就可以听到一切了.
"Whatever you want you shall have , "said the Fairy .
仙女说："你想得到什么,你就可以有什么."
I don't want to be hard on your daughter ; she shan't be pressed .
我不想对你女儿太严厉,她不会太受压的.
I promise that you shall see her again before long .
我保证你不久就能再见到她.
2）命令
You shall come to my office immediately .你必须马上来我的办公室.
She shall not stay in my garden .她不可以呆在我的花园里.
He shall not come into my study . 不许他进我的书房.
You shall do as you are told .按告诉你的那么做.
3）决心（表示某事一定会发生）
That day shall come .那一天一定会到来.
It has been decided that he shall be given the job .
肯定给他那份工作的事已经定下来了.
This law shall come into effect on January 1st 2001
这个法律于2001年元月1日生效.
4）规定
Each competitor shall wear a number .每个参赛者要佩戴一个数字标.
The renter shall keep the house in a neat and orderly state .
租赁者要保持房屋整洁有序.
The supplier shall make shipment before October and the purchaser shall make payment within 15 days after
receipt of the goods .卖方十月以前装运,买方在收到货物后十五天内付款.
should
（用作情态动词时,有时表示具体的意思,有时却没有意义.主要用于下面几个方面.）
1）表示出于职责、义务该做某事
You shouldn't come to such a decision hastily .
你不应该匆匆忙忙地作出这么一个决定.
You should write to your parents at least once a month .
你应该至少每月给你父母亲写一封信.
We should read English aloud every morning .
我们应该每天早晨朗读英文.
They should do it for their own good .
为了他们自己利益他们应该做这件事.
2）表示对某种情况的估计
She shouldn't be out in such an early morning .
她不会这么一大早就出去了吧.
The effect of the tax should be felt in higher prices .
人们可能会从各种上涨的物价中感觉到这种税的影响的.
The event should lead them to a even worse economic crisis.这次事件可能会将他们引向更严重的经济危机.
This book should be published in two months at most .
这本书最多两个月后就会出版的.
3）表示惊讶、失望等情绪
I think it is dreadful that anyone should be so miserable.
我认为,竟然每个人都如此伤心就太糟糕了.
Why should I pay him for nothing ? 我干吗要无为地付给他钱?
It seems so unfair that this should happen to me .
这件事竟然发生在我身上似乎太不公平了.
It's strange that it should be so cold today .奇怪,今天怎么会这么冷.
4）用于某些从句中表示虚拟语气
The doctor insisted that the girl should be hospitalized .
大夫坚持认为那个女孩要住院治疗.
If it had not been for the doctor's care the girl should not be speaking to you now .要不是由于大夫的精心照料,这个女孩现在就不能与你说话了.
She stood away so that he should enter the room first .
她让到一边,好让他第一个进入房间.
I'll write it down lest I should forget it 我将它记下以免遗忘.
Take an umbrella with you in case it should rain .
带上雨伞,以防万一下雨.
will , would
（would可以看作是will的过去式,这两个词除了时态不相同外,在表达意思的许多方面是相近的.当然will 和would又都有一些各自不同的独特用法.）
1）用于第二人称疑问句,表示请求（在这种用法中would使语气更为客气、委婉）
Will you tell her that I'll be back in twenty minutes ?
请告诉她我二十分钟后回来,好吗?
If you want help, just let me know , will you ?
你需要帮助就告诉我,好吗?
Won't you come in and have a little whisky ?
你要不要进来喝一点儿威士忌?（或是：你进来喝一点儿威士忌,好吗?）
Would you tell me how to get to the shopping center ?
您能告诉我怎么去购物中心吗?
2）用于表示愿望
Go where you will .去你想去的地方吧.
I will pay you at the rate you ask .我会按你要的利率付给你钱的.
He wouldn't let the doctor take his blood pressure .他不愿意让大夫给他量血压.
They had to obey whether they would or not .他们不得不遵从他们的意愿.
3）表示习惯、倾向（可译成"总是会、老是,等" ）
Sometimes the cat will lie there all afternoon .
有时侯,那只猫总是整个下午都躺在那儿.
Oil and water will not mix .油和水决不能调和.
He would sit there for hours , doing nothing at all .
他总是在那儿一坐就是几个小时,什么都不干.
4）表示猜测（可译成"一定是……、想必……,等" ）
This will be the house you're looking for .这想必就是你要找的房子吧.
He will have gone back to New Zealand .他一定是回新西兰去了.
The person you mentioned would be the father , is that right ?
你说的那个人一定是爸爸了,对吗?
That would be in 1999 , I think .那大概是在1999年吧.
5）will用于表示决心（可译成"一定要,决心,等" ）
We will never talk about that subject again .
我们决不会再谈论这个话题了.
I will make this computer work even if I have to stay up all night .
我即使整晚不睡觉也一定要让这台计算机工作起来.
6）would常用于虚拟条件句,表示与事实相反或不太可能实现的情况
But for your help we would have been late .要不是你帮忙我们就迟到了.
Well , I wouldn't worry about it . It won't do me any good .
好了,我不会担心那件事的,因为它不会给我带来什么好处
can't是can的否定形式.