情态动词有can (could), may (might), must, have to, shall (should, will (would), dare (dared), need (needed), ought to等。 情态动词无人称和数的变化；不能单独使用，必须与其后的动词原形构成谓语
一、 can, could
1) 表示能力（体力、知识、技能）。 Can you lift this heavy box?（体力） Mary can speak three languages.（知识） Can you skate?（技能） 此时可用be able to代替。Can只有一般现在时和一般过去式；而be able to则有更多的时态。
I’ll not be able to come this afternoon.
当表示“经过努力才得以做成功某事”时应用be able to，不能用Can。如：
He was able to go to the party yesterday evening in spite of the heavy rain. 2) 表示请求和允许。 -----Can I go now?
----- Yes, you can. / No, you can’t. 此时可与may互换。在疑问句中还可用could, might代替，不是过去式，只是语气更委婉，不能用于肯定句和答语中。
---- Could I come to see you tomorrow? ---- Yes, you can. ( No, I’m afraid not. )
3) 表示客观可能性（客观原因形成的能力）。
They’ve changed the timetable, so we can go by bus instead.
This hall can hold 500 people at least. 4) 表示推测（惊讶、怀疑、不相信的态度），用于疑问句、否定句和感叹句中。 Can this be true?
This can’t be done by him. How can this be true?
二、 may, might
1) 表示请求和允许。might比 may语气更委婉，而不是过去式。否定回答时可用can’t
或mustn’t，表示“不可以，禁止”。 ----Might/ May I smoke in this room? ---- No, you mustn’t.
---- May/Might I take this book out of the room? ---- Yes, you can. (No, you can’t / mustn’t. ) 用May I...？征徇对方许可时比较正式和客气，而用Can I...？在口语中更常见。 2）用于祈使句，表示祝愿。 May you succeed!
3) 表示推测、可能性（不用于疑问句）。 might不是过去式，它所表示的可能性比may小。 1．He may /might be very busy now.
2．Your mother may /might not know the truth.
三、 must, have to
1) 表示必须、必要。 You must come in time.
在回答引出的问句时，如果是否定的，不能用mustn’t（禁止，不准），而用needn’t, don’t have to（不必）. ---- Must we hand in our exercise books today? ---- Yes, you must.
---- No, you don’t have to / you needn’t. 2) must是说话人的主观看法， 而have to则强调客观需要。Must只有一般现在时， have to 有更多的时态形式。 1． he play isn’t interesting, I really must go now. 2． I had to work when I was your age. 3) 表示推测、可能性（只用于肯定的陈述句）
1． You’re Tom’s good friend, so you must know what he likes best.
2． Your mother must be waiting for you now.
四、 dare, need
1) dare作情态动词用时, 常用于疑问句、否定句和条件从句中, 过去式形式为dared。 1． How dare you say I’m unfair?
2． He daren’t speak English before such a crowd, dare he?
3． If we dared not go there that day， we couldn’t get the beautiful flowers.
2) need 作情态动词用时, 常用于疑问句、否定句。在肯定句中一般用must, have to, ought to, should代替。 1．You needn’t come so early. 2. ---- Need I finish the work today? ---- Yes, you must. / No, you needn’t.
3) dare和 need作实义动词用时， 有人称、时态和数的变化。在肯定句中，dare后面常接带to的不定式。在疑问句和否定句中，dare后面可接带to或不带to的不定式。而need后面只能接带to的不定式。 1. I dare to swim across this river. 2. He doesn’t dare (to) answer.
3. He needs to finish his homework today.
五、 shall, should
1) shall 用于第一人称，征求对方的意见。 What shall we do this evening?
2) shall 用于第二、三人称，表示说话人给对方的命令、警告、允诺或威胁。
1. You shall fail if you don’t work hard.(警告) 2. He shall have the book when I finish it.(允诺)
3. He shall be punished.(威胁)
六、 will, would
1) 表示请求、建议等，would更委婉。 Will / Would you pass me the ball, please? 2) 表示意志、愿望和决心。 1. I will never do that again.
2. They asked him if he would go abroad.
3) would表示过去反复发生的动作或某种倾向。would表示过去习惯时比used to正式，且没有“现已无此习惯”的含义。
1. During the vacation, he would visit me every other day.
2. The wound would not heal. 4) 表示估计和猜想。
It would be about ten o’clock when she left home.
七、 should, ought to
1) should, ought to表示“应该”，ought to表示义务或责任，比should语气重。
1. I should help her because she is in trouble. 2. You ought to take care of the baby.
2) 表示劝告、建议和命令。should, ought to可通用，但在疑问句中常用should。
1. You should / ought to go to class right away. 2. Should I open the window? 3) 表示推测
should , ought to (客观推测), must(主观推测)。
1.He must be home by now. (断定他已到家) 2.He ought to/should be home by now.(不太肯定) 3. This is where the oil must be.(直爽)
4. This is where the oil ought to/should be.(含蓄)
1 情态动词的语法特征
1） 情态动词不能表示正在发生或已经发生的事情，只表示期待或估计某事的发生。
2） 情态动词 除ought 和have 外，后面只能接不带to 的不定式。
3） 情态动词没有人称，数的变化，即情态动词第三人称单数不加-s。
4） 情态动词没有非谓语形式，即没有不定式，分词，等形式。
2 比较can 和be able to
1）can could 表示能力；可能 (过去时用could), 只用于现在式和过去式(could)。be able to可以用于各种时态。
They will be able to tell you the news soon. 他很快就能告诉你消息了。
2）只用be able to a. 位于助动词后。 b. 情态动词后。
c. 表示过去某时刻动作时。 d. 用于句首表示条件。
e. 表示成功地做了某事时，只能用was/were able to， 不能用could。
He was able to flee Europe before the war broke out. = He managed to flee Europe before the war broke out.
注意：could不表示时态
1）提出委婉的请求，（注意在回答中不可用could）。 --- Could I have the television on?
--- Yes, you can. / No, you can't.
2）在否定，疑问句中表示推测或怀疑。 He couldn't be a bad man. 他不大可能是坏人。
3 比较may和might
1） 表示允许或请求；表示没有把握的推测；may 放在句首，表示祝愿。
May God bless you! He might be at home.
注意： might 表示推测时，不表示时态。只是可能性比may 小。
2） 成语： may/might as well，后面接不带to 的不定式，意为\"不妨\"。
If that is the case, we may as well try.
典型例题
Peter ___come with us tonight, but he isn't very sure yet.
A. must B. may C. can D. will
答案B. 表可能性只能用may. 此句意可从后半句推出。
4 比较have to和must
1) 两词都是'必须'的意思，have to 表示客观的需要， must 表示说话人主观上的看法，既主观上的必要。
My brother was very ill, so I had to call the doctor in the middle of the night. 我弟弟病得很厉害，我只得半夜里把医生请来。(客观上需要做这件事)
He said that they must work hard. 他说他们必须努力工作。（主观上要做这件事）
2) have to有人称、数、时态的变化，而must只有一种形式。但must 可用于间接引语中表示过去的必要或义务。 He had to look after his sister yesterday.
3） 在否定结构中： don't have to 表示\"不必\" mustn't 表示\"禁止\"，
You don't have to tell him about it. 你不一定要把此事告诉他。
You mustn't tell him about it. 你一定不要把这件事告诉他。
5 must表示推测
1) must用在肯定句中表示较有把握的推测，意为\"一定\"。 2) must表对现在的状态或现在正发生的事情的推测时， must 后面通常接系动词be 的原形或行为动词的进行式。 You have worked hard all day.You must be tired. 你辛苦干一整天，一定累了。（对现在情况的推测判断） He must be working in his office. 他一定在办公室工作呢。 比较：
He must be staying there. 他现在肯定呆在那里。 He must stay there. 他必须呆在那。
3) must 表示对已发生的事情的推测时，must 要接完成式。 I didn't hear the phone. I must have been asleep. 我刚才没有听到电话，我想必是睡着了。
4) must表示对过去某时正发生的事情的推测，must 后面要接不定式的完成进行式。
---Why didn't you answer my phone call?
---Well, I must have been sleeping, so I didn't hear it.
5) 否定推测用can't。
If Tom didn't leave here until five o'clock, he can't be home yet. 如果汤姆五点才离开这儿，他此时一定还未到家。
6 表示推测的用法
can, could, may, might, must 皆可表示推测，其用法如下：
1）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。 I don't know where she is, she may be in Wuhan. 2）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。
At this moment, our teacher must be correcting our exam papers.
这时，我们老师想必在批改试卷。
3）情态动词+动词完成时。 表示对过去情况的推测。
We would have finished this work by the end of next December.
明年十二月底前我们很可能已完成这项工作了。 The road is wet. It must have rained last night. 地是湿的，昨天晚上一定下雨了。
4）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。
Your mother must have been looking for you. 你妈妈一定一直在找你。
5）推测的否定形式，疑问形式用can't, couldn't表示。 Mike can't have found his car, for he came to work by bus this morning.
迈克一定还没有找回他的车，因为早上他是坐公共汽车来上班的。
注意：could, might表示推测时不表示时态，其推测的程度不如can, may。
7 情态动词+ have +过去分词
1) may(might) have + done sth, can (could) have + done sth 表示过去，推测过去时间里可能发生的事情。 Philip may (might) have been hurt seriously in the car accident.
Philip can (could) have been hurt seriously in the car accident.
2) must have +done sth，对过去时间里可能发生的事情的推测，语气较强，具有\"肯定\"，\"谅必\"的意思。 ---Linda has gone to work, but her bicycle is still here.
---She must have gone by bus.
3) ought to have done sth, should have done sth 本应该做某事，而事实上并没有做。否定句表示\"不该做某事而做了\"。
You ought to (should) have been more careful in this experiment.
He ought not to have thrown the old clothes away.（事实上已扔了。）
ought to 在语气上比should 要强。
4) needn't have done sth 本没必要做某事
I dressed very warmly for the trip, but I needn't have done so. The weather was hot.
5) would like to have done sth 本打算做某事 I would like to have read the article, but I was very busy then.
8 should 和ought to
should 和ought to 都为\"应该\"的意思，可用于各种人称。 ---Ought he to go?
---Yes. I think he ought to.
表示要求，命令时，语气由 should（应该）、had better最好）、must（必须）渐强。
9 had better表示\"最好\"
had better 相当于一个助动词，它只有一种形式，它后面要跟动词原形。 had better do sth had better not do sth
It is pretty cold. You'd better put on my coat. She'd better not play with the dog.
had better have done sth表示与事实相反的结果，意为\"本来最好\"。
You had better have come earlier.
10 would rather表示\"宁愿\"
would rather do would rather not do
would rather„ than„ 宁愿„„而不愿。
还有would sooner, had rather, had sooner都表示\"宁愿\"、\"宁可\"的意思。
If I have a choice, I had sooner not continue my studies at this school.
I would rather stay here than go home. = I would stay here rather than go home.
典型例题
----Shall we go skating or stay at home? ----Which ___ do?
A. do you rather B. would you rather C. will you rather D. should you rather
答案B。本题考查情态动词rather的用法，would rather +do sth 意为\"宁愿\"，本题为疑问句，would 提前，所以选B。
11 will和would 注意：
1）would like； Would like to do = want to 想要，为固定搭配。
Would you like to go with me?
2）Will you„? Would you like„? 表示肯定含义的请求劝说时，疑问句中一般用some, 而不是any。
Would you like some cake?
3）否定结构中用will，一般不用would, won't you是一种委婉语气。
Won't you sit down?
12 情态动词的回答方式
问句 肯定回答 否定回答
Need you„? Yes, I must. No,I needn't Must you„? /don't have to.
典型例题
1）---Could I borrow your dictionary? ---Yes, of course, you____. A. might B. will C. can D. should
答案C.could表示委婉的语气，并不为时态。答语中of course，表示肯定的语气，允许某人做某事时，用can和 may来表达，不能用could或might。复习： will 与you连用，用来提出要求或下命令。should与you 连用，用来提出劝告。
2）---Shall I tell John about it?
---No, you ___. I've told him already.
A. needn't B. wouldn't C. mustn't D. shouldn't 答案A。needn't 不必，不用。 wouldn't 将不, 不会的。 mustn't 禁止、不能。 shouldn't 不应该。本题为不需要，不必的意思，应用needn't。
3）---Don't forget to come to my birthday party tomorrow. ---______.
A. I don't B. I won't C. I can't D. I haven't 答案B. will既可当作情态动词，表请求、建议、也可作为实义动词表\"意愿、意志、决心\"，本题表示决心，选B。
13 带to 的情态动词
带to 的情态动词有四个：ought to, have to, used to, be to, 如加上have got to ,(=must), be able to，为六个。它们的疑问，否定形式应予以注意：
Do they have to pay their bill before the end of the month?
She didn't use to play tennis before she was fourteen. You ought not to have told her all about it.
Ought he to see a heart specialist at once.?
ought to 本身作为情态动词使用。其他的词作为实义动词使用，变疑问，否定时，须有do 等助动词协助。
典型例题
Tom ought not to ___ me your secret, but he meant no harm.
A.have told B.tell C.be telling D. having told 答案A。由于后句为过去时，告诉秘密的动作又发生在其前因，此地应用过去完成时，但它在情态动词 ought to 后，所以用have。
14 比较need和dare
这两词既可做实义动词用，又可做情态动词用。作为情态动词，两者都只能用于疑问句，否定句和条件句。 need 作实义动词时后面的不定式必须带to，而dare作实义动词用时, 后面的to 时常可以被省略。 1) 实义动词： need （需要, 要求） need + n. / to do sth
2) 情态动词： need，只用原形need后加do，否定形式为need not。 Need you go yet?
Yes, I must. / No, I needn't.
3) need 的被动含义：need, want, require, worth（形容词）后面接doing也可以表示被动： need doing = need to be done
[编辑本段]can和could的用法
1. 表示能力或客观可能性，还可以表示请求和允许。如： Can you finish this work tonight? Man cannot live without air. — Can I go now? — Yes, you can.
注意：①could也可表示请求，语气委婉，主要用于疑问句，不可用于肯定句，答语应用can（即could不能用于现在时态的简略答语中）。如： Could I come to see you tomorrow?
Yes, you can. （否定答语可用No, I'm afraid not.） ②can表示能力时，还可用be able to代替。如： I'll not be able to come this afternoon.
2. 表示惊异、怀疑、不相信的态度。（主要用在否定句、疑问句或惊叹句中）
Can this be true?
How can you be so careless! This cannot be done by him.
3. ―can(could) + have + 过去分词‖的疑问或否定形式表示对过去发生的行为怀疑或不肯定。如：
He cannot have been to that town. Can he have got the book?
4. 用在疑问句及否定句中,表示惊讶,不相信等.
5. cannot```too\\enough表示\"无论怎样``````也不过分\越``````越好\" [编辑本段]may和might的用法 1. 表示许可。
表示请求、允许时，might比may的语气更委婉一些，否定回答时要用mustn't表示―不可以‖、―禁止‖、―阻止‖之意。如： You may drive the car.
— Might I use your pen? — No, you mustn't.
用May I ... 征询对方许可在文体上比较正式，在口气上比较客气。在日常口语中，用Can I ... 征询对方意见在现代口语中更为常见。 2. 用于祈使句中表示祝愿。如： May you succeed!
3. 表示推测、可能（疑问句不能用于此意）。 He may be very busy now.
4. ―may(might) + have + 过去分词‖表示对过去发生的行为的推测。如： He may not have finished the work. [编辑本段]must和have to的用法
1. 表示必须、必要。（must表示主观多一些而have to则表示客观多一些）如：
You must come in time.
回答must引出的问句时，如果是否定的回答，不能用mustn't，而要用needn't或don't have to。
— Must we hand in our exercise books today?
— Yes, you must. (No, you don’t have to.)
2. ―must be + 表语‖的结构表示推测，它的否定或疑问式用can代替must。
This must be your pen.
3. ―must + have + 过去分词‖的结构常用在肯定句中，表示对过去发生的行为的推测。它的否定或疑问式用can代替must。 He must have been to Shanghai.
4. have to的含义与must相似，两者往往可以互换使用，但have to有各种形式，随have的变化而定。must与have to有下列几点不同： ① must表示的是说话人的主观看法，而have to则往往强调客观需要。如：
The play is not interesting. I really must go now. I had to work when I was your age.
② must一般只表现在，have则有更多的时态形式。 ③ 二者的否定意义不大相同。如： You mustn't go. 你可不要去。 You don't have to go. 你不必去。 ④ 询问对方的意愿时应用must。如： Must I clean all the room? [编辑本段]dare和need的用法
1. need表示―需要‖或―必须‖，作情态动词时，仅用于否定句或疑问句中，在肯定句中一般用must, have to, ought to,或should代替。如： You needn’t come so early. — Need I finish the work today? — Yes, you must.
注意：needn't + 不定式的完成式―表示本来不必做某事而实际上做了某事‖。如：
You needn't have waited for me.
2. Dare作情态动词时，主要用于疑问句、否定句和条件从句中，一般不用在肯定句中。如： How dare you say I'm unfair.
He daren't speak English before such a crowd, dare he?
3. Dare和need常用作实义动词，有时态、人称和数的变化，所不同的是，作实义动词时，在肯定句中，dare后面通常接带to的不定式，在否定和疑问句中，dare后面可接带to或不带to的不定式。如： I dare to swim across this river. He does not dare (to) answer. Don't you dare (to) touch it! I wondered he dare (to) say that. He needs to finish it this evening. [编辑本段]shall和should的用法
1. Shall用于第一人称，表示征求对方的意愿。如： What shall we do this evening?
2. Shall用于第一、第三人称疑问句中，表示说话人征求对方的意见或向对方请示。如：
Shall we begin our lesson?
When shall he be able to leave the hospital?
3. Shall用于第二、第三人称，表示说话人给对方命令、警告、允诺或威胁。如：
You shall fail if you don't work harder. （警告） He shall have the book when I finish reading. （允诺）
He shall be punished. （威胁）
4. Should表示劝告、建议、命令，其同义词是ought to；在疑问句中，通常用should代替ought to。如： You should go to class right away. Should I open the window?
Should的含义较多，用法较活，现介绍三种其特殊用法。请看下面的句子：
① I should think it would be better to try it again. 我倒是认为最好再试一试。
② You are mistaken, I should say. 依我看，你是搞错了。 ③ I should advise you not to do that. 我倒是劝你别这样做。 ④ This is something I should have liked to ask you. 这是我本来想问你的。
从以上例句可以看出：情态动词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。
Should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：
⑤ 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。
⑥ If you should change your mind, please let us know. 万一你改变主意，请通知我们。
⑦ Should I (If I should) be free tomorrow I will come. 万一我明天有时间，我就来。
此外，Why(or How) + should结构表示说话人对某事不能理解，感到意外、惊异等意思。意为―竟会‖。如：
⑧ Why should you be so late today? 你几天怎么来得这么晚？ ⑨ — Where is Betty living? — 贝蒂住在哪里？ — How should I know? — 我怎么会知道呢？
⑩ 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。
5. ―should + have + 过去分词‖结构一般表示义务，表示应该做到而实际上没有做到，并包含一种埋怨、责备的口气。如： She should have finished it.
I should have helped her, but I never could. You should have started earlier. [编辑本段]will和would的用法
1. 表示请求、建议等，would比will委婉客气。如： Would you pass me the book? 2. 表示意志、愿望和决心。如： I will never do that again.
They asked if we would do that again.
3. 用―will be‖和―will(would) + have + 过去分词‖的结构表示推测，主要用于第二、三人称。前者表示对目前情况的推测，后者表示对已经完成的动作或事态的推测。如： This will be the book you want. He will have arrived by now.
The guests would have arrived by that time. I thought you would have finished this by now.
4. Would可表示过去反复发生的动作或某中倾向。Would表过去习惯时比used to正式，并没有―现已无此习惯‖的含义。如： The wound would not heal.
During the vacation he would visit me every week. 5. 表料想或猜想。如：
It would be about ten when he left home. What would she be doing there?
I thought he would have told you all about it. [编辑本段]ought to的用法 1. Ought to表示应该。如： You ought to take care of him.
2. 表示推测。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） This is where the oil must be. （比较直率） This is where the oil ought to be. （比较含蓄）
3. ―ought to + have + 过去分词‖表示过去应做某事而实际未做。如： You ought to have asked him (but you didn't). 这时，ought to和should可以互相换用。
注意：在美国英语中，ought to用于否定句和疑问句时，to可以省略。如：
Ought you smoke so much? You oughtn't smoke so much.
[编辑本段]used to，had better，would rather的用法
1. Used to表示过去的习惯动作或状态，现在已不存在，在间接引语中，其形式可不变。如：
He told us he used to play football when he was young. 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.
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 used to smoke, but it was a long time ago. I certainly did use to smoke, but it was a long time ago. 其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） Did you use to play chess? Yes, I did.
Used you to get up early in the morning? Yes, I did. (Yes, I used to.) 2. Had better意为―最好‖，后接不带to的不定式。如： — 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）
注：①had best与had better同意，但较少用。②You had better … 用于同辈或小辈，对长辈不可用。
3. Would rather意为―宁愿‖，表选择，后接不带to的不定式。如： I'd rather not say anything. Would you rather work on a farm? — Wouldn't you rather stay here? — No, I would not. I'd rather go there.
由于would rather表选择，因而后可接than。如： I would rather work on a farm than in a factory. I would rather watch TV than go to see the film.
I would rather lose a dozen cherry trees than that you should tell me one lie.
I'd rather you didn't talk about this to anyone. （句中的'd rather不是情态动词，would在此是表愿望的实义动词） [编辑本段]can (could), may (might), 用法:
can (could) 表示说话人能,可以,同意,准许,以及客观条件许可,could 为 can 的过去式。
Can you pass me the books? 你能给我递一下书吗 ? Could you help me, please? 请问,你能帮助我吗? What can you do? 你能干点什么呢? Can you be sure? 你有把握吗?
can 和could 只能用于现在式和过去式两种时态,将来时态用 be able to 来表示。
He could help us at all. 他完全可以帮助我们。
With the teacher's help,I shall be able to speak English correctly. 由于老师的帮助,我将能准确地讲英语。
may (might) 可以, 表示说话人同意,许可或请求对方许可。 You may take the book home. 你可以把书带回家去. May I come in? 我可以进来吗?
May I use your dictionary? 我可以用你的词典吗? You may put on more clothes. 你可以多穿点衣服.
He said he might lend us some money. 他说他可以借给我们一些钱。
may 否定式为 may not, 缩写形式是 mayn't.
might 是may 的过去式, 有两种用法, 一种表示过去式，一种表示虚拟语气, 使语气更加委婉, 客气或对可能性的怀疑。 He told me he might be here on time. 他说他能按时间来。
Might I borrow some money now. 我可以借点钱吗? He might be alive. 他可能还活着。
[编辑本段]must, need, ought to, dare (dared)用法
Must 必须,应该,一定,准是, 表示说话人认为有必要做某事, 命令, 要求别人做某事以及对事物的推测。
must 用来指一般现在时和一般将来时, 过去式可用 have to 的过去式代替。
I must finish my work today. 我今天必须完成我的工作。 You mustn't work all the time. 你不能老是工作。 Must I return the book tomorrow? 我必须明天还书吗?
After such a long walk, you must be tired. 走了这么长的路,你一定困了。
He must be the man I am looking for. 他一定是我要找的人。 He had to go because of somebody's calling him that day. 那天他要走是因为有人叫他。
must + have + 过去分词,表示现在对过去事物的推测。 He must have told my parents about it. 他一定把这件事情告诉我父母亲了。 He must have received my letter now. 他现在一定收到我的信了。
It's six o'clock already, we must have been late again. 已经六点钟了，我们一定又迟到了。
must 和 have to 的区别: must 表示说话人的主观思想, have to 表示客观需要。
You must do it now.
你必需现在就干。(说话人认为必须现在干) I have to go now.
我得走了。(客观条件必须现在走) need 需要 多用在否定式或疑问句中. Need I attend the meeting tomorrow? 我需要明天参加会议吗?
You need not hand in the paper this week. 这一周你不必交论文。
need 是一个情态动词, 他的用法完全和其他情态动词一样, 但 need 还可当作实义动词使用, 这时 need 就象其他动词一样,有第三人称,单复数, 后面加带 to 的动词等特性。 I need a bike to go to school. 我上学需要一辆自行车。 Do you need a dictionary? 你需要词典吗? She needs a necklace. 她需要一条项链。
needn't + have + 过去分词 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。
dare 敢 多用在否定或疑问句中。 The little girl dare not speak in public. 小女孩不敢在公众面前说话。 Dare you catch the little cat? 你敢抓小猫吗?
dare 除用作情态动词外,更多的是当实义动词使用, 用法同实义动词一样,要考虑人称,单复数,时态等。 Do you dare to walk in the dark? 你敢黑夜走路吗？
He doesn't dare to tell the teacher what happened that day. 他不敢告诉老师那天发生的事。
[编辑本段]ought，will ，Shall, should，have to ought 应当,应该 后面跟带有 to 的动词不定式。
You ought to read these books if you want to know how to repair the motorcar.
如果你想知道如何修理汽车,你应该读这些书。 You ought to bring the child here. 你应该把孩子带来。
ought + to have done 句型。指过去动作,表示一件事情该做而未做。 You ought to have been here yesterday. 你昨天就应该来。
ought not to have done 句型。表示一件不该做的事情却做了。 You ought not to have taken the book out of the reading-room. 你不应该把书带出阅览室。
will (would)决心,愿望。 would 为 will 的过去式, 可用于各人称。
I'll do my best to catch up with them. 我要尽全力赶上他们。
I'll never do it again, that's the last time. 我再不会做那件事情了,这是最后一次。
He said he would help me. 他说他会帮助我。
will, would用于疑问句表示说话人向对方提出请求或询问,用 would 比 will 更婉转,客气。
It's hot. Will you open the windows? 天气太热了,你能打开窗户吗? Will you help me to work it out? 你能帮我解这道题吗? Would you like some coffee？ 给你来点咖啡怎样？
Shall, should表示命令,警告,允诺,征求,劝告,建议惊奇。 You should hand in the exercise book. 你应该交作业本儿了。 This should be no problem. 这应该没问题。 Shall we go now. 我们现在可以走了吗? Why should I meet him？ 为什么我要见他?
have to,不得不,必须,表示客观条件只能如此, 而must 则表示主观思想必须。
I have to go now. 我现在得走了。
I have to cook for my child. 我得给孩子做饭。
You must be here on time next time. 你下次一定要按时来。
We must go to get the timetable ourselves. 我们一定要自己去拿时刻表。
as 和 like 在汉语中都译做\"像\但字面下的隐含意思是不同
的.
like侧重A B两者间的比较,并不意味着A和B属于一类或完全相似. 例如:He speak English like an Englishman.(=in a way an Englishman speaks English.) 表示有些相象
as则侧重于同一性,意味着A B两者属于同一类或完全相似. 例如:He speaks English as an Englishman.(=as well as an English.) 表示讲得一样好
as与like是英语中常见的两个词,他们的语义和用法很多.在语义上者两个词都可以当\"像......\正如......\"讲,说明人与人、物与物、动作与动作、状态与状态之间的相似之处。但其语法结构却是不一样的。 一、当―像‖讲时，语法结构的不同之处是：
1、as作连接词。她引导比较状语从句和方式状语从句，而且这两种从句通常为省略句。例如：
1、She is a fine singer, as her mother used to be. 2、There is as much water in this cupas in that one.
2、like作介词。例如： 3、My sister isn''t much like me. 4、The robot can''t work like man.
如果需要加强语气，再这两个词之前加上just之类的词即可。例如： 5、All the plants and animals need air just as they need water. 6、Mary goes to school at seven every morning just like her brother. 含义不同之处是：
(1)like只是单纯表示比较，而且通常不是同类事物进行比较： 7、The ship looks like a high building. 8、The sky was like ink over my head. (2)as可表示同类事物比较。 9、This ship is as long as that one.
二、当―正如....‖意义讲时，语法结构的不同之处是： (1)as作关系代词或关系副词、引导定于从句。
as 在这样的句子里指全句所谈到的内容，引出非限制性定于从句，在从句中一般做主语或宾语。例如：
10、Metals have many good properties, as has been stated before. 11、As we said before, you have done a good job. (2)like作界词。
12、She, like thousands of others, is fascinated by this work. 三、as与like有时可以换用。
(1)在非正式的美国英语中like可用作连词，代替as.例如：
13、Nobody loves you like I do, baby.
(2)在非正式的文体中，like，常被用来代替as if.
14、Duke said:\"You feel like you could reach out and touch it (the space).\"
四、as常用于下列词组：在as you know ,as we agreed, as you suggested 这些词组中，as的实际意义不是比较，也不是相似，而是同一事物或人之义。例如：
as you know 的意思不是you know somthing like this ,而是you know this.
15、As he knew, she wasn''t much at letter-writing.
16、As all his friends agree, he was unusually warm-hearted,loving and generous.
在非正式问题中，有时可以在这种词组里用like,但在受过教育的人所使用的英语中不多见
as 和 like 在汉语中都译做\"像\但字面下的隐含意思是不同的. like侧重A B两者间的比较,并不意味着A和B属于一类或完全相似. 例如:He speak English like an Englishman.(=in a way an Englishman speaks English.) 表示有些相象
as则侧重于同一性,意味着A B两者属于同一类或完全相似. 例如:He speaks English as an Englishman.(=as well as an English.) 表示讲得一样好
as与like是英语中常见的两个词,他们的语义和用法很多.在语义上者两个词都可以当\"像......\正如......\"讲,说明人与人、物与物、动作与动作、状态与状态之间的相似之处。但其语法结构却是不一样的。 一、当―像‖讲时，语法结构的不同之处是：
1、as作连接词。她引导比较状语从句和方式状语从句，而且这两种从句通常为省略句。例如：
1、She is a fine singer, as her mother used to be. 2、There is as much water in this cupas in that one. 2、like作介词。例如： 3、My sister isn''t much like me. 4、The robot can''t work like man.
如果需要加强语气，再这两个词之前加上just之类的词即可。例如： 5、All the plants and animals need air just as they need water. 6、Mary goes to school at seven every morning just like her brother. 含义不同之处是：
(1)like只是单纯表示比较，而且通常不是同类事物进行比较： 7、The ship looks like a high building. 8、The sky was like ink over my head. (2)as可表示同类事物比较。 9、This ship is as long as that one.
二、当―正如....‖意义讲时，语法结构的不同之处是： (1)as作关系代词或关系副词、引导定于从句。
as 在这样的句子里指全句所谈到的内容，引出非限制性定于从句，在从句中一般做主语或宾语。例如：
10、Metals have many good properties, as has been stated before. 11、As we said before, you have done a good job. (2)like作界词。
12、She, like thousands of others, is fascinated by this work. 三、as与like有时可以换用。
(1)在非正式的美国英语中like可用作连词，代替as.例如： 13、Nobody loves you like I do, baby.
(2)在非正式的文体中，like，常被用来代替as if.
14、Duke said:\"You feel like you could reach out and touch it (the space).\"
四、as常用于下列词组：在as you know ,as we agreed, as you suggested 这些词组中，as的实际意义不是比较，也不是相似，而是同一事物或人之义。例如：
as you know 的意思不是you know somthing like this ,而是you know this.
15、As he knew, she wasn''t much at letter-writing.
16、As all his friends agree, he was unusually warm-hearted,loving and generous.
在非正式问题中，有时可以在这种词组里用like,但在受过教育的人所使用的英语中不多见
as与like是英语中常见的两个词,他们的语义和用法很多.在语义上者两个词都可以当\"像......\正如......\"
讲,说明人与人、物与物、动作与动作、状态与状态之间的相似之处。但其语法结构却是不一样的。一、当“像”讲时，语法结构的不同之处是：1、as作连接词。她引导比较状语从句和方式状语从句，而且这两种从句通常为省略句。例如：1、She is a fine singer, as her
mother used to be.2、There is as much water in this cupas in that one.2、like作介词。例如：3、My sister isn''t much like me.4、The robot can''t work like man.如果需要加强语气，再这两个词之前加上just之类的词即可。例如：5、All the plants and animals need air just as they need water.6、Mary goes to school at seven every morning just like her brother.含义不同之处是：(1)like只是单纯表示比较，而且通常不是同类事物进行比较：7、The ship looks like a high building.8、The sky was like ink over my head.(2)as可表示同类事物比较。9、This ship is as long as that one.二、当“正如....”意义讲时，语法结构的不同之处是：(1)as作关系代词或关系副词、引导定于从句。as 在这样的句子里指全句所谈到的内容，引出非限制性定于从
句，在从句中一般做主语或宾语。例如：10、Metals have many good properties, as has been stated before.11、As we said before, you have done a good job.(2)like作界词。12、She, like thousands of others, is fascinated by this work.三、as与like有时可以换用。(1)在非正式的美国英语中like可用作连词，代替as.例如：13、Nobody loves you like I do, baby.(2)在非正式的文体中，like，常被用来代替as if.14、Duke said:\"You feel like you could reach out and touch it (the space).\"四、as常用于下列词组：在as you know ,as we agreed, as you suggested 这些词组中，as的实际意义不是比较，也不是相似，而是同一事物或人之义。例如：as you know 的意思不是you know somthing like this ,而是you know this.15、As he knew, she wasn''t much at letter-writing.16、As all his friends agree, he was unusually warm-hearted,loving and generous.在非正式问题中，有时可以在这种词组里用like,但在受过教育的人所使用的英语中不多见。
as if 是似乎，好像的意思，作连词用。 as 也可以作连词，但意思是因为，由于。 as和like都可以作介词，意思是好象。 alike只能作表语。
1.as 和LIKE 在谈到人，事物或动作彼此有相同点或共同点时 两者皆可 LIKE是介词 用于名词和代词之前 Like me, she enjoys all kings of music.他和我一样 各种音乐都喜爱。
AS是连词 用于分句之前 如She enjoys all kinds of music,as I do.她各种音乐都喜爱 和我一样
在口语中 like 往往用作连词，当作AS 和AS IF 使用 如No nody understands him like/as I do.没有人能象我这样理解他。
It looks like / as if he won't arrive in time.看来他好象不能按时到达了 2.比较AS和LIKE 用于职业或作用方面的用法
She worked as a teacher for many years.她当了许多年的教师。 Our doctor always talks to me like a teacher talking to a child.给我们看病的医生对我说话总是象教师对小学生说话一样。 3.as if 是好象、似乎、仿佛的意思
4.Alike 是形容词 作表语 相同、一样、相似的意思 The twins don't look at all alike.这对双胞胎一点都不象
也可作副词 表示同样的 The climate here is always hot,summer and winter alike.这里的气候总是那么热，夏季和冬季都一样
1. can (could)
1）表示能力，could主要指过去时间。
Two eyes can see more than one. 两只眼比一只眼看得清。
Could the girl read before she went to school? 这女孩上学前能识字吗？ 2）表示可能（理论上或是逻辑判断上）。
The temperature can fall to –60℃, that is 60℃ below freezing. 气温可降至—60℃，也就是零下60℃。
He can´t (couldn´t) have enough money for a new car. 他不可能有足够的钱买新车。
You mustn´t smoke while you´re walking around in the wood. You could start a fire.
在林子里走时勿吸烟，那样可能会引起火灾。 3）表示允许。
Can I have a look at your new pen? 我可以看一看你的新钢笔吗？ He asked whether he could take the book out of the reading—room. 他问他可不可以把书带出阅览室。
4）表惊异、怀疑、不相信等态度。主要用于否定句、疑问句或感叹句中。 Where can (could) they have gone to? 他们会去哪儿了呢？ He can´t (couldn´t) be over sixty. 他不可能超过六十岁。 How can you be so careless? 你怎么这么粗心？ 5）比较委婉客气地提出问题或陈述看法。 Can (Could) you lend me a hand? 帮我一把好吗？
I´m afraid we couldn´t give you an answer today. 恐怕我们今天不能给你答复。 2. may (might)
1）表允许，might可以指过去时间，也可指现在时间，语气更委婉。 You may take whatever you like. 你喜欢什么就拿什么。
He told me that I might smoke in the room. 他告诉我可以在房间里抽烟。 May (Might) I ask for a photo of your baby? 我可以要一张你宝宝的照片吗？
在回答以may引起的问句时，多避免用这个词，而用其它方式，如Yes, please. / Certainly.
/ Please don´t ./ You´d better not. / No, you mustn´t.等，以免显得太严峻或不客气。
2）表可能（事实上）。可以指过去时间，也可以指现在时间，但语气更加不肯定。
He may be at home. 他可能在家。
She may not know about it. 她可能不知道这件事。
He was afraid they might not agree with him. 他担心他们可能不同意他的意见。
They might be having a meeting, but I´m not sure. 他们有可能在开会，不过我不肯定。 3. must
1）表示义务。意为―必须‖（主观意志）。
We must do everything step by step. 我们一切都必须循序渐进地做。
You mustn´t talk to her like that. 你不可能那样对她说话。
--Must we hand in our exercise—books now? 我们现在就要交练习本吗？
--No, you needn´t. / No, you don´t have to. 不必。（这种情况下，一般不用mustn´t）
2）表示揣测。意为―想必、准是、一定‖等，只用于肯定句。 He must be ill. He looks so pale. 他准是病了。他的脸色苍白。 She´s wearing a diamond necklace. She must have a lot of money. 她戴着钻石项链，一定很有钱。 4. shall
1）表征询意见，用于第一、第三人称疑问句。 Shall I get you some tea? 我给你点茶好吗？ Shall the boy wait outside? 让那男孩在外面等吗？ What shall we do this evening? 我们今晚做什么？
2）表说话人的意愿，有―命令、允诺、警告、决心‖等意思，用于第二、第三人称陈述句。
You shall do as I say. 按我说的做。（命令）
You shall have my answer tomorrow. 你明天可以得到我的答复。（允诺） He shall be sorry for it one day, I tell you. 有一天他会后悔的，我告诉你。（警告）
Nothing shall stop us from carrying out the plan. 什么也不能阻止我们执行这项计划。（决心） 5. will
1）表意愿，用于各种人称陈述句。
I will do anything for you. 我愿为你做任何事。
None is so blind as those who won´t see. 不愿看的人眼最瞎。 If you will read the book, I´ll lend it to you. 如果你愿意读这本书，我会把它借给你。
2）表请求，用于疑问句。
Will you close the window? It´s a bit cold. 请你把窗户关上好吗？有点冷。
Won´t you drink some more coffee? 再来一点咖啡好吗？ 3）表示某种倾向或习惯性动作。
Fish will die out of water. 鱼离开水就不能活。 The door won´t open. 这门打不开。
The boy will sit there hour after hour looking at the traffic go by. 那男孩常常坐在那里好几个钟点，看着车辆行人通过。 6. should
1）表义务。意为―应该‖（某件事宜于做），用于各种人称。 You should be polite to your teachers. 你对老师应该有礼貌。 You shouldn´t waste any time. 你不应该浪费时间。 2）表推测，意为―想必一定、照说应该、估计‖等。
The film should be very good as it is starring first—class actors. 这部新电影是一流演员主演的，估计拍得很好。
They should be home by now. 照说他们现在应当已经到家了。 7.would
1）表意愿。
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。
I said I would do anything for you. 我说过我愿意为你做任何事。 2）表委婉地提出请求、建议或看法。
Would you like another glass of beer? 再来杯啤酒好吗？ Would you mind cleaning the window? 请把窗户擦一下好吗？ They wouldn´t have anything against it. 他们不会有什么反对意见。 3）表过去反复发生的动作或过去的一种倾向。
Every time she was in trouble, she would go to him for help. 她每遇到麻烦都会向她求助。他告诉我盒子打不开了。
（二）情态动词后跟完成式和进行式的用法
1.情态动词后跟完成式，表―应当已经……‖，―想必已经……‖，―本来可以……‖等意。
I should have finished the work earlier. 我应当早一点完成这项工作的。 He isn´t here. He must have missed the train. 他还未到，一定是没赶上火车。
Where can (could) he have gone? 他能到那里去了呢？
You may (might) have read about it. 你可能在报上已经读到这件事了。 You could (might) have been more careful. 你本来可以更细心的。 He needn´t have worried about it. 他本不必为此事担心。
There was a lot of fun at yesterday´s party. You ought to have come, but why didn´t you?
昨天的聚会非常有意思。你本应该来，为何不来呢？
2. 情态动词后跟进行式，表示―想必正在……‖，―可能正在……‖，―应当正在‖等意。
It´s twelve o´clock. They must be having lunch. 现在是十二点。他们一定正在吃饭。
They may be discussing this problem. 他们可能正在论讨这个问题。 He can´t be telling the truth. 他说的不可能是真话。
She shouldn´t be working like that. She´s still so weak. 她不应当那样干，她身体仍那么虚。 （三）几组词的辨异 1. can 和be able to
1）情态动词can只有两种时态形式，现在式can和过去式could，而be able to有多种时态形式。
Mary can play the piano. She has been able to play it since she was 5. 玛丽会弹钢琴。她五岁起就会弹了。
2）用在过去时中，could经常表示能够做某事，事实上不一定去做，而was∕were able to则表示―过去做成了某事‖。在否定句中两者可通用。 He could swim across the English Channel. But he didn´t feel like it that day.
他能游过英吉利海峡，但那天他不想游。
Yesterday I was able to get home before the heavy rain. 昨天我在下大雨前赶到了家里。
2. must和 have to
must表示主观意志，而have to表示由于客观因素不得不做某事。must没有过去式，除在间接引语中可用于表示过去时间，在直接引语中表示过去时间应该用had to代替。
I told her that she must give up smoking. 我叫她必须戒烟。
We had to get everything ready that night. 我们那晚得把一切准备就绪。 3. would和used to
1）used to表示过去与现在或过去某时与后来的情况有不同，而would只表过去的情况。
People used to think that the earth was flat.
过去人们认为地球是平的。（现在人们不这么认为。）
She would go out for a walk in the morning when she was in the country. 在乡下时，她总是在早晨去散会儿步。（可能现在仍有散步的习惯。） 2）used to可表示过去的习惯动作和经常的情况，而would只表示过去的习惯动作。
He used to ∕would smoke while writing. 过去他写东西时常抽烟。
She used to be fat. 她过去很胖
情态动词主要有can/could，may/might，must，shall/should，will/would，need，ought to等。情态动词具有如下特征：
1.情态动词本身具有意义，而且在不同场合表示不同的情态意义。例如：
You must finish the homework first.你必须先完成家庭作业。
The road is wet. It must have rained last night.地面是湿的，昨晚一定下过雨了。
2.情态动词通常后接动词原形，构成谓语。而且情态动词第三人称单数的现在时没有词形变化，即没有-s形式、-ing形式和-ed形式。
3.形态动词有现在时和过去时形式，如may/might，但在许多场合中过去时并不表示过去。例如：
Could you leave a message please?(表示委婉的请求)请留个口信好吗？
Would you like to go to the party with me?(表示邀请)你和我一起去参加晚会好吗？
难点释疑
一、can/could与be able to用法比较
1.在肯定句中，can/could用于表示具有某种能力，而be able to表示过去一次特定的能力，即表示在某特定场合设法成功做成某事，相当于manage to do或者succeed in doing。因此，can/could和be able to不能互换。例如：
I can sing many English songs.我会唱许多英文歌曲。
We were able to return to our campsite before the heavy rain.我们在下大雨前设法会到了野营地。
He was able to swim across the river and escaped being caught.他游到了河对岸，没有被抓住。
2.在否定句中，can/could与be able to几乎没有什么差别，两者可以互换。例如：
She wasn’t able to/couldn’t cook French dishes.她不会做法国菜。
二、must，need与have to比较
1.must和need引导的疑问句，其肯定回答和否定回答是一样的。例如：
—Must I finish the work tonight?我必须在今晚完成工作吗？
—Yes, you must./No, you needn’t/don’t have to/don’t need to.是的，必须。/不，不必。
—Need I finish the work tonight?需要我在今晚完成工作吗？
—Yes, you must./No, you needn’t/don’t have to/don’t need to.是的，必须。/不，不必。
2.must与have to的区别在于，must多表示主观上认为必须干某事，而have to多表示客观上不得不干某事。例如：
I must go over the test paper again to see if there are any mistakes.我必须再检查一遍试卷看看是否有错误。
The teacher said that there were many mistakes in my test paper, so I had to go over it again.老师说我试卷中有很多错误，所以我只好再检查一遍。
3.不要简单地认为must没有否定形式，mustn’t意为―不准‖，例如：
You mustn’t cheat in the exam.你不准在考试中作弊。
4.在肯定句中，need只能作实义动词；在否定句中，need既可以作实义动词，又可以作情态动词。例如：
I need to have a rest after such a long journey.走了那长的路，我需要休息一下。
You needn’t do/don’t need to do that exercise since you understand it.既然懂了，你就不必作那个练习了。
三、should，ought to与need
should/ought to + have done表示本来应该做某事结果却没有做，shouldn’t/oughtn’t to + have done表示本来不应该做某事结果却做了，needn’t have done表示本来不需要做某事结果却做了。例如：
These flowers have died. You should have watered them by more water.这些花死了，你应该给它们多浇一点水的(事实上没有)。
The president admitted that the war was unjust. He oughtn’t to have waged it.总统承认这场战争是非正义的，他不应该发动这样的战争(战争已经开始了)。
Since I have placed an order, you needn’t have placed another one.由于我已经下了订单，你本不需要在下一份的(已经下了另一份订单)。
四、情态动词表示推测语气
1.情态动词表推测这一知识点要求考生进行重点掌握。对现在的事情进行肯定判断时，一般用must/may加动词原形，此时，must不再表示―必须‖，而是表示―肯定‖，may表示―也许‖，否定判断时一般用can't加动词原形，此时，can’t不再表示―不能够‖，而是表示―肯定不……、肯定没有……‖。对过去的事情进行肯定判断时，用must/may加动词的完成时形式，同样，must不再表示―必须‖，而是表示―肯定‖，may表示―也许‖，否定判断时一般用can't加动词的完成时形式，can’t不再表示―不能够‖，而是表示―肯定不……、肯定没有……‖。例如：
The road is wet. It must have rained.路面很湿，一定下过雨了。
I met him on his way home. He can’t be in the library now.我在他回家的路上遇见了他，他现在不可能在图书馆。
2.必须掌握情态动词表示推测语气时的反意疑问句。例如：
The road is wet. It must have rained, hasn’t it?
The road is wet. It must have rained last night, didn’t it? (多了过去时的时间状语)
I met him on his way home. He can’t be in the library now, isn’t he?
The coat is too close to the fire. It might get burnt, doesn’t it?
五、shall的特殊用法
shall通常与第一人称I和we连用，表示征求对方意见或者提出建议。例如：
Shall I take down this picture?要我取下这幅画吗？
Shall we book the tickets now?我们现在去订票好吗？
但是，在某些情况下shall可以与第二、三人称连用，表示―责令‖、―请求‖，例如：
You shall obey my orders! 你们必须服从我的命令！
He has waited outside for half an hour. Shall he come in? 他在外面等了半小时了，要让他进来吗？
六、will的特殊用法
1.用于叙述真理时，用will。例如：
Oil will float on water.油能浮在水面上。
Man will die.人总会死的。
2.用于表示具有某种功能时，用will。例如：
The door will not open.门打不开。
The car will not start.车子启动不了。
（四）情态动词的基本用法 1. can (could)
1）表示能力，could主要指过去时间。
Two eyes can see more than one. 两只眼比一只眼看得清。
Could the girl read before she went to school? 这女孩上学前能识字吗？ 2）表示可能（理论上或是逻辑判断上）。
The temperature can fall to –60℃, that is 60℃ below freezing. 气温可降至—60℃，也就是零下60℃。
He can´t (couldn´t) have enough money for a new car. 他不可能有足够的钱买新车。
You mustn´t smoke while you´re walking around in the wood. You could start a fire.
在林子里走时勿吸烟，那样可能会引起火灾。 3）表示允许。
Can I have a look at your new pen? 我可以看一看你的新钢笔吗？ He asked whether he could take the book out of the reading—room. 他问他可不可以把书带出阅览室。
4）表惊异、怀疑、不相信等态度。主要用于否定句、疑问句或感叹句中。 Where can (could) they have gone to? 他们会去哪儿了呢？ He can´t (couldn´t) be over sixty. 他不可能超过六十岁。 How can you be so careless? 你怎么这么粗心？ 5）比较委婉客气地提出问题或陈述看法。 Can (Could) you lend me a hand? 帮我一把好吗？
I´m afraid we couldn´t give you an answer today. 恐怕我们今天不能给你答复。 2. may (might)
1）表允许，might可以指过去时间，也可指现在时间，语气更委婉。 You may take whatever you like. 你喜欢什么就拿什么。
He told me that I might smoke in the room. 他告诉我可以在房间里抽烟。
May (Might) I ask for a photo of your baby? 我可以要一张你宝宝的照片吗？
在回答以may引起的问句时，多避免用这个词，而用其它方式，如Yes, please. / Certainly.
/ Please don´t ./ You´d better not. / No, you mustn´t.等，以免显得太严峻或不客气。
2）表可能（事实上）。可以指过去时间，也可以指现在时间，但语气更加不肯定。
He may be at home. 他可能在家。
She may not know about it. 她可能不知道这件事。
He was afraid they might not agree with him. 他担心他们可能不同意他的意见。
They might be having a meeting, but I´m not sure. 他们有可能在开会，不过我不肯定。 3. must
1）表示义务。意为―必须‖（主观意志）。
We must do everything step by step. 我们一切都必须循序渐进地做。 You mustn´t talk to her like that. 你不可能那样对她说话。
--Must we hand in our exercise—books now? 我们现在就要交练习本吗？
--No, you needn´t. / No, you don´t have to. 不必。（这种情况下，一般不用mustn´t）
2）表示揣测。意为―想必、准是、一定‖等，只用于肯定句。
He must be ill. He looks so pale. 他准是病了。他的脸色苍白。 She´s wearing a diamond necklace. She must have a lot of money. 她戴着钻石项链，一定很有钱。 4. shall
1）表征询意见，用于第一、第三人称疑问句。 Shall I get you some tea? 我给你点茶好吗？ Shall the boy wait outside? 让那男孩在外面等吗？ What shall we do this evening? 我们今晚做什么？
2）表说话人的意愿，有―命令、允诺、警告、决心‖等意思，用于第二、第三人称陈述句。
You shall do as I say. 按我说的做。（命令）
You shall have my answer tomorrow. 你明天可以得到我的答复。（允诺） He shall be sorry for it one day, I tell you. 有一天他会后悔的，我告诉你。（警告）
Nothing shall stop us from carrying out the plan. 什么也不能阻止我们执行这项计划。（决心） 5. will
1）表意愿，用于各种人称陈述句。
I will do anything for you. 我愿为你做任何事。
None is so blind as those who won´t see. 不愿看的人眼最瞎。 If you will read the book, I´ll lend it to you. 如果你愿意读这本书，我会把它借给你。
2）表请求，用于疑问句。
Will you close the window? It´s a bit cold. 请你把窗户关上好吗？有点冷。
Won´t you drink some more coffee? 再来一点咖啡好吗？ 3）表示某种倾向或习惯性动作。
Fish will die out of water. 鱼离开水就不能活。 The door won´t open. 这门打不开。
The boy will sit there hour after hour looking at the traffic go by. 那男孩常常坐在那里好几个钟点，看着车辆行人通过。 6. should
1）表义务。意为―应该‖（某件事宜于做），用于各种人称。 You should be polite to your teachers. 你对老师应该有礼貌。 You shouldn´t waste any time. 你不应该浪费时间。 2）表推测，意为―想必一定、照说应该、估计‖等。
The film should be very good as it is starring first—class actors. 这部新电影是一流演员主演的，估计拍得很好。
They should be home by now. 照说他们现在应当已经到家了。 7.would 1）表意愿。
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。
I said I would do anything for you. 我说过我愿意为你做任何事。 2）表委婉地提出请求、建议或看法。
Would you like another glass of beer? 再来杯啤酒好吗？
Would you mind cleaning the window? 请把窗户擦一下好吗？ They wouldn´t have anything against it. 他们不会有什么反对意见。 3）表过去反复发生的动作或过去的一种倾向。
Every time she was in trouble, she would go to him for help. 她每遇到麻烦都会向她求助。他告诉我盒子打不开了。 8. ought to
1）表义务，意为―应该‖（因责任、义务等该做），口气比should稍重。 You are his father. You ought to take care of him. 你是他父亲，应当管他。
You oughtn´t to smoke so much. 你不应该抽这么多烟。 2）表推测，暗含很大的可能，语气较弱。
Han Mei ought to know his telephone number. 韩梅该知道他的电话号码。
There´s a fine sunset; it ought to be a fine day tomorrow. 今天有晚霞，明天应该是个好天。 9. used to
表示过去的习惯动作或状态，现在不复发生或存在。疑问式和否定式有两种。
He used to live in the countryside, but now he lives in the city.他过去住在乡下，现在住在城里。
There used to be a building at the street corner, but it has been pulled down.
街道拐角处过去有座楼房，现在拆了。
I usedn´t (didn´t use) to smoke. 我过去不抽烟。
Used you (Did you use) to go to school on foot? 你过去常步行去学校吗？
重点疑难
（一）need和dare的用法
need和dare既可用作情态动词，也可用作实义动词。用作情态动词时，主要用于否定句和疑问句。用作实义动词时，可用于各种句式。 1.用作情态动词
--Need I come? --Yes, you must. --我需要来吗？ --需要。 You needn´t telephone him now. 你现在不必打电话给他。 I don´t think you need worry. 我想你不必发愁。
She dare not go out alone at night. 她晚上不敢一个人出去。 How dare you say I´m unfair? 你竟敢说我不公平？
Not one of them dared mention this. 他们谁也不敢提这件事。 2.用作实义动词
You don´t need to do it yourself. 你不必亲自做这件事。 We need to tell them the news. 我们需要把这消息告诉他们。 The table needs painting (to be painted.). 桌子需要油漆一下。 We should dare to give our own opinion. 我们要敢于提出自己的观点。 He did not dare (to) look up. 他不敢抬头看。 I dare day he´ll come again. 我想他会再来的。
（cI dare say…为固定习语）
（二）情态动词后跟完成式和进行式的用法
1.情态动词后跟完成式，表―应当已经……‖，―想必已经……‖，―本来可以……‖等意。
I should have finished the work earlier. 我应当早一点完成这项工作的。 He isn´t here. He must have missed the train. 他还未到，一定是没赶上火车。
Where can (could) he have gone? 他能到那里去了呢？
You may (might) have read about it. 你可能在报上已经读到这件事了。 You could (might) have been more careful. 你本来可以更细心的。 He needn´t have worried about it. 他本不必为此事担心。
There was a lot of fun at yesterday´s party. You ought to have come, but why didn´t you?
昨天的聚会非常有意思。你本应该来，为何不来呢？
2. 情态动词后跟进行式，表示―想必正在……‖，―可能正在……‖，―应当正在‖等意。
It´s twelve o´clock. They must be having lunch. 现在是十二点。他们一定正在吃饭。
They may be discussing this problem. 他们可能正在论讨这个问题。 He can´t be telling the truth. 他说的不可能是真话。
She shouldn´t be working like that. She´s still so weak. 她不应当那样干，她身体仍那么虚。 （三）几组词的辨异
1. can 和be able to
1）情态动词can只有两种时态形式，现在式can和过去式could，而be able to有多种时态形式。
Mary can play the piano. She has been able to play it since she was 5. 玛丽会弹钢琴。她五岁起就会弹了。
2）用在过去时中，could经常表示能够做某事，事实上不一定去做，而was∕were able to则表示―过去做成了某事‖。在否定句中两者可通用。 He could swim across the English Channel. But he didn´t feel like it that day.
他能游过英吉利海峡，但那天他不想游。
Yesterday I was able to get home before the heavy rain. 昨天我在下大雨前赶到了家里。 2. must和 have to
must表示主观意志，而have to表示由于客观因素不得不做某事。must没有过去式，除在间接引语中可用于表示过去时间，在直接引语中表示过去时间应该用had to代替。
I told her that she must give up smoking. 我叫她必须戒烟。
We had to get everything ready that night. 我们那晚得把一切准备就绪。 3. would和used to
1）used to表示过去与现在或过去某时与后来的情况有不同，而would只表过去的情况。
People used to think that the earth was flat.
过去人们认为地球是平的。（现在人们不这么认为。）
She would go out for a walk in the morning when she was in the country.
在乡下时，她总是在早晨去散会儿步。（可能现在仍有散步的习惯。） 2）used to可表示过去的习惯动作和经常的情况，而would只表示过去的习惯动作。
He used to ∕would smoke while writing. 过去他写东西时常抽烟。 She used to be fat. 她过去很胖
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