情态动词的用法
A. can; could; be able to
Can 1. 表示“能力”(此时过去时是could)
2.表示许可、请求，“可以”。--Can/Could I go now?
3 表示推测, 把握很大,could也可表推测,把握比can小。
--Look! Someone is coming! Who can it be?
--It can’t be him. He has gone to Paris.（不可能）/ He could be here soon. 他很快就来。
4 表示感情（惊异/不耐烦）“究竟，到底”（主要用于否定句，疑问句和感叹句中。）
How can you be so foolish?
What can it possibly be? 到底那是怎么一回事?
They can’t be working at this time of day.
5 肯定句中客观存在的可能性。“有时会，偶尔”
It can be quite windy there, especially in spring.
Could 1.表示能力，can 的过去式，过去能够
Could you speak English then? 那时候你会说英语吗?
2. 请求允许（委婉语气）（问句的答语不用could，而用can，）
Could [Can] I use your pen? ” “Yes, of course you can.”/ No, I’m afraid not.
3. 表示推测可能性（肯，否，疑）
We could go there this summer. 今年夏天我们可能要去那儿。(将来可能性)
You could be right, but I don’t think you are. 你可能是对的，但我并不认为你是对的。
4. could have done ①对过去推测，可能已经。。。②本来能够却没做，差点就
He can’t [couldn’t] have seen her there. 他不可能在那儿见到她。
He could have gone home. 他可能已回家了
He could have told her, but he didn’t choose to. 他本来可以告诉她的，但他却没有。
B. may 和might
1.表示允许﹑许可，might提问更委婉。
---May/Might I watch TV after supper?
---Yes, you may./ Yes, please./ Certainly.
---No, you mustn't. / No, you may not. / No, you can’t./No, you’d better not.
2. 表示推测，有“或许”、“可能”的意思。might把握更小。疑问句用can/ could.
?He may/might be right./ I hear there may be a few copies left.
?He may/might come today (tomorrow).
3. may表示祝愿，倒装。May +主语+动词原形。May you succeed!/May you all be happy. ☆may [might] as well…意为“不妨”、“还是…为好”等，用might 比用may 语气更委婉。如：I’m ready，so I might as well go now．我已准备好，因此不妨现在就走。
There’s nothi ng to do, so I may [might] as well go to bed.
☆may well... 完全可能
C. must, have to
Must 1. 表示“必须”。否定式mustn’t表示“不可以”、“不准”、“禁止”等。
Everybody must obey the rules../You mustn’t lend it to others./You mustn’t speak like that to your mother.
☆在回答有“must” 的询问时，--- Must I go now? --- Yes, you must.
---No, you needn’t. / No, you don’t have to.
2. must表示推测（“一定”、“必定”），表肯定的推测, 其否定的推测用can’t，表示“不可能”。You must be hungry after the long walk. / It can't be Jim, for he has gone to Beijing.
The Chinese language must have the large number of speakers.
3．must 表示说话人不耐烦的态度，“干嘛偏要”
☆must + have + done，表示对过去事物的肯定推测。“一定做过...”
He must have told my parents about it. 他一定把这件事情告诉我父母亲了。
☆must表示推测时，其反意疑问句应根据动词的实际时态而变化。如：?It must be nice to take a walk here, isn’t it?
?Tom buys a lot of apples ,he must like eating them, doesn't he？
Must have done 的反意疑问句有三种情况:
①从句中含有过去的时间状语,反意疑问句用过去时.
?The ground is wet , it must have rained last night, didn’t it?
②从句中含有过去完成时的时间状语,反意疑问句用过去完成时.
?By the end of last term, we must have learnt 2000 words, hadn’t we?
③若从句中不含任何时间状语,反意疑问句用现在完成时
?We must have been met somewhere (before), haven’t we?
☆must 表示“必须”“有必要”时，反义疑问句部分用mustn’t...? 或needn’t ...?
You must go home right now, needn’t you?
☆must 用否定形式mustn’t时，附加疑问句部分用may或must…?
You mustn’t cheat in the examination, must you?
3. 表示与说话人愿望相反及不耐烦．意为“偏要”．
-____you make so much noise?
-Sorry, I will take care not to. A Must B Can C May D Would
4. must 和have to 的区别:
D. ought to/ should/ shall
Ought to ought to用于反映客观情况或涉及义务和规定时，常译作“应该”、“应当”(和should差不多，只是语气较强)，有时表示非常可能的事情。
?There ought not to be much noise in a hospital.
?--- Ought he to go? --- Yes, he ought to.
?If she is completely well, she ought to be back at school today.
ought to have done指过去动作,表示一件事情该做而未做。
ought not to have done 表示一件不该做的事情却做了。
should 1.用于表示劝告和建议，“应该”．表示自己的主观看法,语气比ought to弱。
☆should + have done 指过去动作,表示一件事情该做而未做。
should not + have done 表示一件不该做的事情却做了。
--- Who did it sound like? Anybody you know?
--- Well, perhaps Jeff. I should have asked who was calling before he hung it up.
2.表推测，“按道理，按常理应该”
They should have arrived by two o’ clock.
3.表示惊讶,赞叹，不满，责备“竟然”
I am sorry that you should do such a thing.
4. 用于if引导的虚拟条件句中，表示一件事听起来可能性小，但也不是完全不可能。有“万一”的意思
Should I be free tomorrow, I’ll come.
Ask Tom to ring me up if you should see him.
shall
1. shall 作为情态动词，用于第二、第三人称，陈述句，表示说话人的意愿，有“命令”、“警告”、“威胁”、“强制”、“允诺”等意思。“必须，应，可以”．
?You shall do as I say. （命令）
?Tell him that he shall have the book tomorrow. （允诺）
?You shall be punished if you break the law. (表警告)
2. 用于第一、第三人称, 在疑问句中，shall 用来征询对方意见。“……好吗？”“要不要……？”
Where shall I wait for you?/ Shall he come at once?/ Shall we start the meeting now? 3.在条约﹑规定﹑法令等文件中表示义务或规定，用于第三人称
The new regulation shall take effect on June 1st.
E. will 和would
1) 表示“意志”、”决心”、“意愿”，可用于多种人称。will 指现在，would 指过去。
?I will tell you all about it./ He won’t go.
(2) 表示询问对方的意愿或向对方提出请求,在疑问句中用语第二人称时，委婉语气would.
?I’m going to go shopping after school. Will you go with me?
?Will/would you please give him a message when you see him?
(3) 表示习惯动作，有“总是”、“惯于”的意思。过去式would
He’ll talk for hours if you give him the chance.
(4) 表示功能，“能”
The door won’t open. / The car won’t start.
(5)will用于叙述真理,客观规律时“会”
Oil will float on water. / Fish will die without water.
F. need 和dare
1. need 表示“需要”、“必须”。通常用在否定句或疑问句中。
?He needn’t pay for it.
--- Need you go now? --- Yes, I must. --- No, I needn’t.
2. dare 表示“敢”。通常用于否定句、疑问句、条件从句和if/whether 引出的宾语从句中。
?How dare you say I’m unfair?
?She dare not do so.
?He asked me if I dared speak English in public.
☆need 和dare 也可用作行为动词，变化与一般动词相同
?She didn’t need to go.
?--- Who dares to go? - -- I don’t dare (to) go.
☆I dare say …作插入语,我想, 大概, 可能, 或许
☆“needn‘t + have done” 表示过去做了没必要做的事情。
You needn't have taken it seriously. 这件事情你不必太认真。
G. had better “最好”
— We had better go now.
— Yes, we had (we'd better / we had better).
Hadn't we better stop now? (Had we better not stop now?)
I think I'd better be going. （用于进行时态，表“最好立即”）
You had better have done that. （用于完成时态，表未完成动作）
Ⅵ情态动词+ have done
1、must have done,“一定做过/一定已经．．．”，表示对过去情况极大把握地推测，仅用于肯定句
2、may/might have done 也许做过某事（推测）；本来可以做某事却没做
3、can't have done 为否定句或疑问句,对过去的推测“不可能，一定没做过某事”
could have done本来可以做某事却没做
4. needn’t have done 表示”不必要做某事，但做了”，而needn’t do 则表示”不必做(也没做)”
5.、ought to /should have done 表示”本来应当做的却没做”
oughtn’t / shouldn’t have done 本来不应该做某事却做了
6、would/could/might/should + have done 用来表示与过去事实相反的虚拟语气
7、would rather have done 表示”当时宁愿做了某事”，否定形式：would rather not have done
e.g. If I had been free that day, I would have gone with you.
9、would like/love to have done 表示”本想做某事”而实际上未做。
一．情态动词的现在完成式的用法
情态动词现在完成式主要有两个功能：表示已经发生的情况和表示虚拟语气。在这两个方面must / mustn’t; can / can’t ; need / needn’t; may / mayn’t; might / mightn’t; should / shouldn’t; ought等情态动词＋完成式表示的意思是有一定区别的
1．表示已经发生的情况。
1）must have+过去分词，表示对已发生情况的肯定推测，译为“（昨天）一定……”。如：
My pain apparent the moment I walked into the room，for the first man I met asked sympathetically：”Are you feeling all right？”
[A] must be [B] had been [C] must have been [D] had to be
（答案为C）
2）can’t / couldn’t have+过去分词，表示对已发生情况的否定推测，译为“（昨天）一定没……”。如：
Mary my letter; otherwise she would have replied before now.
[A] couldn’t have received [B] ought to have received
[C] has received [D] shouldn’t have received
（答案为A）
3）may / might have +过去分词，表示对已发生的事情做不肯定、可能性很小的推测，或事实上根本没发生，译为“也许……”。如：
At Florida Power’s Crystal River plant，a potentially serious leakage of radioactive water may have been unknowingly caused by an electrician.
2．表示虚拟语气。
1）needn’t have + 过去分词，表示做了不必做的事，相当于”didn’t need to do”，译为“其实没必要……”。如：
You needn’t have come over yourself.
As it turned out to be a small house party，we ______so formally.
[A] needn’t dress up [B]did not need have dressed up
[C] did not need dress up [D] needn’t have dressed up
（没有必要穿的那么正式，体现是说话者的建议，实际结果是否真的穿的很正式没有确定，答案为D）
2）should have +过去分词，表示应该做某事但实际上未做，译为“本应该……”should not + have过去分词表示本不应该做某事但实际上做了，译为“本不应该……”。如：
I regret having left the work unfinished; I should have planned everything ahead carefully.
我本来应该事先认真地把每件事情规划的很好，但实际上作者还是没有规划好，以至工作没有完成。
3）ought to have +过去分词，表示动作按理该发生了，但实际上未发生，译为“该……”，与should 的完成式含义类似。如：
The porter ought to have called the fire-brigade as soon as he saw the fire in the stock，which went up in smoke 。
4）could have +过去分词，表示过去本来可以做但却未做，译为“完全可以……”。这点与ought/should/ have +过去分词用法相似。如：
What you said is right，but you could have phrased it more tactfully.
5）may/ might have +过去分词，表示过去可以做但实际未做，译为“（那样）也许会……”。如：
It might have been better to include more punchy statistics and photos of equipment in the introduction to further assist first-time office automation managers.
二．几个情态动词常考的句型：
1）．may/might （just）as well “不妨，最好”，与had better相近；
Since the flight was cancelled，you might as well go by train.
既然航班已经取消了，你不妨乘火车吧。相当于you had better go by train。
2）cannot / can’t…too …“越……越好，怎么也不过分”。注意这个句型的变体cannot…over…。
如：
You cannot be too careful when you drive a car.驾车时候，越小心越好。
The final chapter covers organizational change and development. This subject cannot be over emphasized 。
3）usedn’t 或didn’t use to 为used to （do）的否定式。
4）should 除了“应该”一层意思外，考研(论坛) 大纲还规定要掌握其“竟然”的意思。如：I didn’t expect that he should have behaved like that. 我无法想象他竟然这样做
三．情态动词被动关系的主动表达法
1．want，require，worth（形容词）后面接doing也可以表示被动意义。
Your hair wants cutting
The book is worth reading
The floor requires washing.
2．need既可以用need to be done 也可以使用need doing ，两种形式都表达被动的意义
The house needs painting= the house needs to be painted.
The watch needed repairing= the watch needed to be repaired
四、情态动词考点
1．推测性情态动词用法
may(可许，可能)，might(可许，可能)，must(一定，必定)，can(或许，可能)均有推测性用法，其中might可能性最小，must可能性最大。may，might，must 常用于肯定句，may，might用于否定句可表示“可能不，can常用于否定句和疑问句，用于否定句表示不可能。
例句：—— Can the man standing there be OUY physics teacher?
—— No．he can’t be our physics teacher．
——站在那边的那个人可能是我们的物理老师吗?
——不，不可能。
—— W i11 she buy you a birthday present?
——她会给你买生日礼物吗
—— She may not．but I’m no so surf~．
——可能不会，但我不太有把握。
2．should的用法
should常表示“应该”，但可置于句首用于条件状语从句(省去if)，表示。万一，还可表示“竟然”。
例句：Should you see the thief,try to catch him．
如果你见到小偷，尽量捉住他。
I can’t imagine such a beautiful girl should be so lazy．
我无法想像这样一个漂亮的女孩竟如此懒惰。
3．may，must，should (shouldn’t)，ought to(oughtn’t to)．needn’t的完成式用法may have done表示“可能已经做了某事，must have done表示“一定已经做了某事”，can’t have done表示“不可能已经做了某事”，should ／ought to have done表示“本来应该做某事但实际未做，shouldn’t／oughtn’t to have done表示本来不应该做某事但实际已做”，needn’t have done
表示“本来没有必要做某事但实际已做”。
例句：Our Chinese teacher isn’t in her office，so she may ／might／must have gone home．
我们的语文老师不在办公室，所以她可能／一定回家了。
I saw his book just now，so he can’t have lost it．
我刚才还见到了他的书，所以他不可能弄丢了这本书。
You failed the exam again．SO you should／ought to have prepared for it．
你考试又失败了，所以你本来是应该为此做好准备的。
There are many mistakes in your article，SO you shouldn’t／oughtn’t have been so careless．
你的文章中有许多错误，所以你本来是不应该这么粗心的。
The exam tum ed out to be so easy,so you needn’t have worried about it．这次考试结果证明这么容易，所以你本来是没有必要为此而担心的。