一、英语中常见情态动词
can, could, may, might, must, have to, ought to, will, would, shall, should, need, dare, used to, had better,would rather.
二、情态动词的特征:
A情态动词有实义但不可作谓语，后接原形动词
B.情态动词有过去式但无第三人称单数形式
C.情态动词否定后加not,变问句放在句首
D.不允许两个意义相近的情态动词连用
【误】Soldiers must have to obey orders.
【正】Soldiers have to obey orders.
【正】Soldiers must obey orders.
【误】Can I be able to borrow two books at a time
【正】Can I borrow two books at a time 【正】Will I be able to borrow two books at a time
三、 情态动词的意义和用法
A. can和could
1．能，会，表示能力
Emily can dance well and her mother could dance well when she was young.
The cinema can seat 1,000 people.这电影院能容纳1，000人。
I could not read such an easy book when I was 7 years old.我七岁时连如此简单的书我也看不懂。
2．可以，表示允许、许可，常用在口语中。could比can语气上要客气。
--- Could I use your dictionary ？
---Yes, go ahead.可以，用吧。
（或Yes, you can.但不能说Yes, you could.）
Could Can you tell me how to get to the zoo 劳驾，你能告诉我怎么去动物园吗？
He asked me whether he could take the book out of the reading room.他问我可不可以把书带出阅览室。
3．可能， 表示推测，常见于疑问句或否定句。can和could没有时态的区别，只表示 can 推测的可能性比could大。
Can he be ill at home？
Can the story be true ？
He cannot be at home.
You mustn't smoke while you are walking around in the woods.
You could start a fire.
4．表示惊异、怀疑、不相信等态度，主要用于否定句和疑问句中。
How can you be so careless
你怎么这么粗心？
Where can could they have gone
他们会去了哪里？
He can't/ couldn't be over sixty.
他不可能超过60岁。
5．could可以表示虚拟
If you had followed my advice, you could have finished it.
If you had tried harder, you could have passed your exam.
６．Can 、 could与be able to的区别
①can表示本能，be able to表示过去经过一番努力才能完成的事情。
【正】Can you speak any foreign languages你会说外语吗？
【正】Are you able to speak any foreign languages 你会说外语吗？
【误】The fire spread the building quickly but everybody could escape.
【正】The fire spread the building quickly but everybody was able to escape.
【正】The fire spread the building quickly but everybody managed to escape.
②be able to比can有更多形式。
No one could answer the question. （这里could可用was able to代替）
When he grows up, he will be able to support his family.
Frank is ill. He hasn't been able to go to school for one week.
I'm sorry for not being able to help you in time.
③在谈论，说话时发生的动作，用can，不用be able to。
【误】Look! I'm able to swim.
【正】Look! I can swim. 看，我会游泳了！
B. may和might
1．“可以” 表示请求、许可， 口语中可用can, could代替may，但在正式场合用may。表示允许时， 也
可用might代替，might不表示过去时，而是表示口气比较婉转。
You may take this seat if you like. May/Can /Could/ Might I have a talk with you ？
--- May/Might I come into the room to see my mother？
--- No, you mustn't. She needs to have a good rest.
提示： May I ...问句常见的肯定回答和否定回答。
肯定回答Yes, please. Certainly. Yes, of course. Sure. Go ahead, please.
否定回答No, you can't.（最常见） No, you mustn't.（具有强烈禁止的意思）
Please don't.
You'd better not.
I don't think you can.
I'm sorry it's not allowed.
2．“可能，也许”表示推测。用于肯定句，否定句中
Your math teacher may/might be in his office. （might表示的可能性很小）
The light isn't on. It maymight be broken. There may might be some ink left in the bottle.
--- Can it be true
--- It may be, or may not be.
3．用在目的状语从句中，构成谓语。
He wants to take a taxi so that he may get there in time.
I arrived at the airport earlier in order that I might meet him.
4．用于祈使句表示祝愿。
May you succeed.祝你成功
May you be happy.祝你快乐。
May that day come soon.希望这一天早日到来。
5. 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。
If that is the case, we may as well try.
C．must和have to
1．must表示主观看法，“必须”。
Everyone must obey the rule. We must do everything step by step.我们必须逐步做每件事。
2．have to表示因客观需要，不得不做某事。
My eyesight is very poor. I have to wear glasses for reading.
You have to pass a test before you can get a driving licence.
提示： 在口语中，我们可以使用have got to来代替have to.
I've got to work on Sunday.
我不得不星期天工作。
When has Ann got to go
安必须什么时候走？
3．must与have to的比较。
①must表示主观的看法，have to表示客观的必要，作“不得不”解）。
I must study hard. 我必须努力学习。（内心的决定）
I have to study hard. 我不得不努力学习。（外界因素逼迫）
②must只有一种形式，而have to可有多种时态。
They had to put off the sports meet due to the bad weather
These last two days he has had to take a rest at home.
③must的否定式和have to的否定式的意思完全不同。
You must keep it a secret. You mustn't tell anyone.（mustn't表示“禁止”）
You don't have to tell me the secret.（don't have to“没有必要”= don't need to）
4．Must 一定 表示推测，肯定程度比may, might, could大得多，只用于肯定句。
①must 加原形动词do ，表示对现在状态的推测。
He must be very lazy for his desk is very untidy.
Carol must get very bored with her job. She does the same thing every day.
②must have done表示对过去的动作或状态的推测。
The ground is wet. It must have rained last night.
I didn't hear the phone. I must have been asleep.
提示：
must表推测只用于肯定句，否定句和疑问句要用can, could
He's just had his lunch. He can't be hungry already.
Leslie walked past me without speaking. He can'tcouldn't have seen me.
注意其反意问句:
You must be hungry after the long walk,aren't you?
He must have gone to Beijing yesterday
5． Must “偏偏，不巧”
Why must it rain today为什么偏偏在今天下雨？
When I was taking a nap, a student must knock at the door.
6. .must 干嘛 / 硬要
Why must you always shout so loudly?
可用来表示根据逻辑推理必然要发生的事，可译为“必然会，总是会”。
Truth must be out. 真相必然会大白的。 Winter must be followed by spring. 冬天到了，春天还会远吗？
D．will和would
1. will和would可表示将要，意愿、决心，用于各种人称陈述句。
will表示将来时间时，不可用于条件状语从句，但will表示意愿或决心时，可用于条件状语从句。
I will do my homework tomorrow
If you will give up smoking, your health will improve.如果你愿意把烟戒掉的话，你的健康状况就会好转。
None is so blind as those who won't see. 不愿看的人眼睛最瞎。
I will never tell you the secret. 我永远不会告诉你这个秘密。
They would not let him in because he was poorly dressed. 他们不让他进去因为他衣着破旧。
2．will和would可用于第二人称疑问句，表示请求和建议等。would比will委婉客气。
Will you have some tea ？
Will you share your happiness with us ？
注： Will / Would you ...表示请求和建议的答复。
肯定回答
Yes, please.是的，请。
Certainly.当然可以。
Sure.当然了。
All right.好啊！
否定回答
I'm sorry. I can't.对不起，不行。
No, thank you.不，不行。
No, I won't.不，不行。
3．will和would可表示某种倾向或习惯性动作。will表示现在的习惯动作，would表示过去的习惯动作。
The boy will sit there hour after hour looking at the traffic go by.
He will surf the Internet every night. 他每天晚上都在上网。
He would be nervous when he met strangers. 遇见陌生人时他总是很紧张。
In class he would ask some silly questions, and his classmates would laugh at him.
4．will可表示某人固执坚持，这时不可使用'll的简略形式。或用于表示物体的固有性质和倾向。
I will take the job, and no one can stop me. 我就要这个工作，没有人可阻止我。
He won't do what he's told. 他就是不愿按所吩咐的去做。
The window won't open. 窗子打不开。
E．shall和should
1．shall ①表示征询意见或请求指示，用于一、三人称疑问句。
Shall I open the window
我打开窗子好吗？
Will you open the window
你打开窗子好吗？
Shall they wait outside ？
Shall the waiter bring meals to your room 要服务员把饭送到你房间去吗？
②表示 “命令、警告、决心、允诺、强制、威胁”等意思，用于第二、三人称陈述句中。
You shall do as I say. （命令）
He shall be sorry for it one day, I tell you. （警告）
You shall fall behind in your exam if you
keep playing.
Nothing shall stop us from carrying out
the plan.
什么也阻止不了我们执行这项计划.（决心）
He shall have the book when I finish reading. 我看完这本书就给他看。（允诺）
I shall do my homework after reading this story book. 读完这本故事书后我就做作业。
2．Should
①表示 “应该”（某件事宜于做），用于各种人称。
Children should obey their parents.儿童应该服从他们的父母。
One shouldn't be selfish. 人千万别自私。
②表示意外、惊讶等情绪，常与what, how, why等词连用或用于否定句，
What should she do but cry for help 除了呼救外，她还能干什么？
Why should you be so late today? 你几天怎么来得这么晚？
— Where is Betty living? — 贝蒂住在哪里？
— How should I know? — 我怎么会知道呢？
I don't know why you should think that I did it. 我真不知道你凭什么认为这件事是我干的。
It's strange that he should have done such a thing.
③ should用于第一人称时可以表示说话人的一种谦逊、客气、委婉的语气。
I should think it would be better to try it again. 我倒是认为最好再试一试。
You are mistaken, I should say. 依我看，你是搞错了。
I should advise you not to do that. 我倒是劝你别这样做。
This is something I should have liked to ask you.这是我本来想问你的。
④Should还可以用在if引导的条件从句，表示一件事听起来可能性很小，但也不是完全没有可能。相当 于
“万一”的意思。从句谓语由should加动词原形构成，主句谓语却不一定用虚拟语气。如：
Ask her to ring me up if you should see her. 你万一见到她，请让她给我打个电话。
If you should change your mind, please let us know. 万一你改变主意，请通知我们。
Should I (If I should) be free tomorrow I will come. 万一我明天有时间，我就来。
⑤should表示对现在或以前应做的事却没做的责怪、批评。
You should be washing your clothes. Why are you playing Ping-Pong
你应该在洗衣服（可是你没洗）。为什么你在打乒乓球？
You should have handed in the exercise last week. 你上周就应当交练习。（可你没交，含责备的意思。）
He should have asked me before he took my bike. 他在用我自行车之前应该和我讲一声。
F．ought to
1．表示 “应该”（因责任、义务而该做），口气比should稍重。
We ought to defend our country. 我们应当保卫我们的国家。（每一个公民应尽的义务）
You ought to respect your parents. 你应当尊敬你的父母。
Oughtn't we to do everything possible to stop pollution 难道我们不应当尽可能地制止污染吗？
2．ought to和should一样，表示对现在或以前应做的事却没做的责怪、批评。
You ought to be washing your clothes. Why are you playing Ping-Pong
你应该在洗衣服（可是你没洗）。为什么你在打乒乓球？
You ought to have handed in the exercise last week. 你上周就应当交练习。（可你没交，含责备的意思。）
He ought to have asked me before he took my bike. 他在用我自行车之前应该和我讲一声。
3．ought to与should的比较。
① ought to表示“义务”。在口语中可以用had better或be supposed to来代替ought to
should则是从说话人的个人看法这一角度来讲的，表示建议
You are her mother.
You ought to look after her.
你是她的母亲，你应当照管她。（是道义上的责任，不能和should互换。）
We should encourage him for we are his classmates. 我们应该鼓励他，我们是他的同班同学啊！
If you are not well, you had better ask Alice to go instead. 如果你不舒服，你最好叫艾丽丝代替你去。
I'm supposed to be there at 8 o'clock. 我应该八点到那里。
②ought to和should还可表示非常有可能的事。表示推测。"想必一定，按理应该"之意
They should be there by now, I think.
It ought to be a fine day tomorrow.(极可能是好天)
注意与must表示推测时的区别：
He must be at home by now.
（断定他已到家）
He ought to be home by now.
（不十分肯定）
G．used to 的用法
1. Used to表示过去的习惯动作或状态，现在已不存在。
He used to drink tea but now he drinks coffee. 他过去总是喝茶但现在他喝咖啡了。（强调现在不喝茶了）
I know where there used to be a river here. 我知道这儿以前哪里有条河。（现在没有河了）
He is not what he used to be. 他已不是原来的他了。
在疑问句、否定句、否定疑问句或强调句中，可有两种形式：
疑问句
Did you use to go to the same school as your brother?
Used you to go to the same school as your brother?
否定句
I usedn't to go there.
I didn't use to go there.
注 Usedn't 亦可拼作usen't，但发音皆为[ju:znt]。
否定疑问句
Usen't you to be interested in the theatre?
Didn't you use to be interested in the theatre?
强调句
I certainly did use to smoke, but it was a long time ago.
反意疑问句或简略回答中，也有两种形式：
She used to be very fat, didn't she? （正式）/ use(d)n't she? （口语）
Used you to get up early in the morning? Yes, I did. (Yes, I used to.)
2 . used to 与would表"过去常常"的差别：
①used to表示过去的习惯，现已无此习惯了，而would只表示过去情况，与现在无关，译作总是，总要"，
When he was young, he would smoke a lot.（不含有和现在比较，现在他也许还在抽，也许不抽了。）
He used to live in the country, but now he lives in the city.他过去住在乡下，现在住在城里。
②used to可表示过去的习惯动作或状态，而would只表示过去的习惯动作不表状态，used to 表不确定的
过去时间，常常不带表确指过去的时间状语，而would常带要带有一个特定的时间状语。
【误】We would play hide-and-seek in the fields.
【正】We used to play hide-and-seek in the fields. 我们过去常在田野里玩捉迷藏。
【正】Whenever we were in the country, we would play hide-and-seek in the fields.
每当我们在乡下，我们都在田野里玩捉迷藏。
Kate used to be very thin. 以前凯特非常瘦。（不用would）
Her would sit there, watching ships.（个人愿意）。
H．dare
dare既可用作情态动词，也可用作行为动词，译为“敢”。
1．情态动词dare（过去式dared）
①dare作为情态动词时主要用于疑问句和否定句，一般不用于肯定句中。
I dare not /daren't walk through the forest at night. 我不敢在黑夜穿过森林。
--- Dare you walk through the forest at night 你敢在黑夜穿过森林吗？
--- No, I daren't. 不，我不敢。
He dared not do it last year. 去年他不敢做这事。（dare的过去时为dared）
②可以用于表示怀疑的名词性从句中。
I wonder how he dare say such things. 我真奇怪他怎么竟敢说出这样的话。
We don't know whether he dare climb the mountain. 我们不知道他是否敢爬那座山。
③可以用于条件状语从句中。
If the enemy dare enter the village, we'll fight against them to the end.
如果敌人敢进入村里，我们就和他们战斗到底。
④固定说法I dare say…… How dare you say……?
2．谓语动词，dare在句子中要随着主语的人称和数发生变化。
He will dare any danger.他敢面对任何危险。
He dared me to jump over the stream.他激我跳过小溪。
Did anyone dare to admit it有人敢于承认吗？
I have never dared (to) go back to take a look. 我再也不敢返回去看一眼了。（否定句中to可省略）
3. dare后接动词完成式daren't have done 表"本不敢做而实际做了"。
I daren’t have done it yesterday.but I think I dare now.昨天我没敢这样做，但现在我想我敢。
5. How dare you/he/she/they…?表示说话人对某人的行为表示愤慨。
How dare you ask me such a question?你怎敢问我这样的问题? How dare you say I'm unfair.？
6. I dare say表示“我相信，我认为，可能”。
I dare say you are right. 我认为你是对的。
7 dare sb. to do sth.表示“挑衅，挑起，敢冒(险) ”意思时，只能用作行为动词。
I dare you to cheat me.
谅你也不敢欺骗我。
He dared me to jump over the river
他激我跳过河。
I．need
1．情态动词need（无过去式）
need作为情态动词时，主要用于否定句和疑问句，在肯定句中常被must, have to, ought to, should等情态
动词取代。
You needn't return the book now. You can keep it till next week if you like.
你现在不必还书， 如果愿意，你可以下周还。（needn't = don't have to）
Need I hand in my homework now 我现在就要交家庭作业吗？
对need引起的一般问句的回答：
--- Need he finish the article next week 他要下个星期完成这篇文章吗？
--- Yes, he must. 是的，他必须完成。 --- No, he needn't. 不，他不需要。（= he doesn't have to）
2．行为动词need
need 作行为动词有人称和数的变化（needs，needed），疑问，否定借助于do，可有自己的宾语（可以 是名词，代词，不定式）
如：
They need our help. 他们需要我们帮助。Does he need to go so soon?他这么快就要走吗?
He doesn’t need to go. 他不需要走。
He needs to go. 他想走
The garden needs watering(=to be watered) .花园该浇水了。
He has grown up. We don't need to worry about him. 他已经长大了，我们不必为他担心。
Patience is needed for that job. 干那工作，需要耐心。
J. 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.
You had better have done that.
注①had better have done sth
You had better have come earlier. 你本该来得早一点。
②You had better … 用于同辈或小辈，对长辈不可用。
K、would rather“宁愿”， would rather not do宁愿不
— Wouldn't you rather stay here?
— No, I would not. I'd rather go there.
2. would rather… than… 宁愿…而不愿…
表选择，如：
I would rather watch TV than go to see the film. I'd rather you didn't talk about this to anyone.
L、情态动词表示推测的用法
1. 情态动词must, can, could, may, might表示推测等，且语气由左向右依次减弱
must (一定会，准会) 只用于肯定句；表示有把握的肯定推测，
can (可能)一般用于疑问句或否定句； can’t(不可能)是表示有把握的否定推测
may (也许) 用于肯定句或否定句。may表示没有把握的肯定推测。may not(可能不)
could, might并不表示过去式，只是语气分别比can, may更弱。可用于肯定句、否定句或疑问句中
should, ought to (按理应当), 但较must稍弱。
例如
1）—When can I come for the photos? I need them tomorrow afternoon.
—They ___B_____ be ready by 12:00.
A. can B. should C. might D. need
2） It’s nearly seven o’clock. Jack ____C____ be here at any moment.
A. mus B. need
C. should D. can
must又语气过强；can一般不用于肯定推测；need意义不通，也不用于肯定句。
3) —Is John coming by train?
—He should, but he ___D_____ not. He likes driving his car.
A. must B. Can C. need D. may
答案解析
1） B.should表示“按理应当，大概”。用might语气太不肯定，顾客可能走掉。
2） C.nearly暗示“时间不早了”，“按理应当(should)”Jack“随时(at any moment)”都有可能到达这里。
3 ）D.由他自己喜欢开车推断，“他可能不会(may not)坐火车来”。can not“不可能”，语气太肯定。
2.情态动词+动词原形，表示对现在或将来的情况的推测，此时动词通常为系动词。
例如：
I don't know where she is, she may be in Wuhan. 我不知道她在哪儿，可能在武汉。
3. 情态动词+动词现在进行时，表示对现在或将来正在进行的情况进行推测。例如：
At this moment, our teacher must be correcting our exam papers. 这时，想必我们老师正在批改试卷。
4. 情态动词+动词完成时，表示对过去情况的推测。
例如：
The road is wet. It must have rained last night.地是湿的，昨天晚上一定下雨了。
5.情态动词+动词的现在完成进行时，表示对过去正在发生事情的推测。例如：
Your mother must have been looking for you. 你妈妈一定一直在找你。
M、情态动词+have +过去分词 表示虚拟语气, 表示“本……”。
①表示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。
②ought 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……”，
ought not to have+过去分词表示\"不该做某事而做了\"。ought to 在语气上比should 要强。如：
He ought not to have thrown the old clothes away.他不该把旧衣服扔了。（事实上已扔了。）
You ought to （should） have been more careful in this experiment. 你当时在做试验时应该更仔细点。
③could have +过去分词，表示过去本来可以做但却未做，译为“完全可以……”。
What you said is right， but you could have phrased it more tactfully.
④might 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 statistics and photos of equipment in the introduction.
⑤needn’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……”。
I dressed very warmly for the trip, but I needn't have done so. The weather was hot.
旅行时，我衣服穿得较多，其实没有必要。那时天很热。
You needn’t have come over yourself.
⑥Darenn’t have + 过去分词，表示做了本不敢做的事，
⑦ would like to have done sth表示本打算做某事，但没做。例如：
I would like to have read the article, but I was very busy then. 我想读这篇文章，但太忙了一直没读。
⑧had better have done sth表示\"本来最好\"
You had better have come earlier.
你本该来得早一点。