第1个回答 2011-10-27
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 nothing 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。
第2个回答 2011-10-24
情态动词是一种本身有一定的词义,表示说话人的情绪,态度或语气的动词,但不能单独作谓语, 只能和其他动词原形构成谓语。
情态动词数量不多,但用途广泛,主要有下列:
can (could), may (might), must, need, ought to, dare (dared), shall (should), will (would) .
情态动词的位置:
情态动词在句中放在谓语动词之前, 谓语动词前若有助动词,则在助动词之前,疑问句中, 情态动词则在主语之前。
情态动词的特点:
情态动词无人称和数的变化, 情态动词后面跟的动词需用原形,否定式构成是在情态动词后面加 "not"。 个别情态动词有现在式和过去式两种形式, 过去式用来表达更加客气, 委婉的语气, 时态性不强, 可用于过去，现在或将来。
情态动词的用法:
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。
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。
must + have + 过去分词,表示现在对过去事物的推测。
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。
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。
needn't + have + 过去分词 表示过去做了没必要做的事情。
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。
ought 应当,应该 后面跟带有 to 的动词不定式。
ought + to have done 句型。指过去动作,表示一件事情该做而未做。
ought not to have done 句型。表示一件不该做的事情却做了。
will (would)决心,愿望。 would 为 will 的过去式,
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。
Shall, should表示命令,警告,允诺,征求,劝告,建议惊奇。
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