情態(tài)動詞的用法要點
一． can和could
情態(tài)動詞 用法 例句
can/could
表示能力 1．“I don’t think Mike can type.”
“Yes, he can.”
2．I can speak fluent English now , but I couldn’t last year.
在肯定句中,表示客觀可能性,并不涉及具體某事會發(fā)生,常用來說明人或事物的特征.要表達具體某事實際發(fā)生的可能性時,不用can,需用could,may,might. 1． As a human being, anyone can make a mistake.
2． I’m confident that a solution can be found.
3． He can be very forgetful sometimes.
4． I may stay at home this weekend.（實際可能性）
5． Peter might come to join us.(實際可能性)
6． It will be sunny in the daytime ,but it could rain tonight.(實際可能性)

表示請求和允許.表示請求,口語中常用could代替can,使語氣更委婉. 1． Can we turn the air conditioner on?
2． Any police officer can insist on seeing a driver’s license.
3． In soccer, you can’t touch the ball with your hands.
4． Could you have her call me back when she gets home, please?
5． I wonder if I could just ask you to sign this.
表示對現(xiàn)在的動作或狀態(tài)進行主觀的猜測,主要用在否定句和疑問句中. 1． It can’t be easy caring for a man and a child who are not your own.
2． Can the man over there be our head master?
表示驚異、懷疑、不相信等態(tài)度,主要用在否定句、疑問句和感嘆句中. 1． Can this be an excuse for not giving them help?
2． This can’t be true.
3． How can you be so crazy.
特別說明：
（1） could用來表示請求時,語氣委婉,主要用于疑問句,不能用于肯定句,答語應用can（即：could不能用于現(xiàn)在時態(tài)的簡略答語中）.如：
——Could I use your dictionary?
——Yes, you can.(否定回答可用：No, I’m afraid not.)
(2) can和be able to辨析
can(could)和be able to都可以表示能力,意思上沒有區(qū)別.但can只有現(xiàn)在式和過去式,而be able to則有更多的形式.如：
I’ve always wanted to able to speak fluent English.
Those bags look really heavy, are you sure you’ll be able to carry them on your own?
但是,表示在過去某時的某一場合經(jīng)過一番努力,終于做成了某事,通常不用could,而用was/were able to來表示.這時,was/were able to相當于managed to do或succeed in doing.如：
After the accident it was a long time before she was able to walk again.
The fire was very big, but most people were able to escape from the building.
(3) 慣用形式“cannot …too…”表示“無論怎么……也不（過分）”.如：
You cannot be too careful.你越小心越好.
慣用形式“cannot but+ 不定式（不帶to）”表示“不得不,只好”.如：
I cannot but admire her determination.我不得不欽佩你的決心.

二．may和 might
情態(tài)動詞 用法 例句
may/might 表示允許、許可.否定回答一般用must not/mustn’t,表示“禁止、阻止”之意,但也可以用had better not (最好別)或may not（不可以）,語氣較為委婉. 1． May I come in and wait?
2． ——May I smoke here?
——No, you mustn’t(或No, you’d better not.)
在表示請求、允許時,might比may語氣更委婉些.用May I征詢對方許可在文體上比較正式,在口氣上比較客氣,在日常用語中,用Can I征詢對方意見更為常見. 1． Might I borrow your pen?
2． I wonder if I might speak to your son.
表示可能性的推測,通常用在肯定句和否定句中,含有“或許”“大概”“可能”之意；用might代替may時,則語氣顯得更加不肯定. 1． It may rain this afternoon.
2． She might come to join us this afternoon.
3． I suppose he might have missed the train.

may用于祈使句表示祝愿 1． May you succeed.
2． Long may he live! 愿他能持續(xù)住下去.
3． May you have many more days as happy as this one.
4． May she rest in peace.愿她安息.
慣用句式：
“may well+ 動詞原形”,意為“完全能,很可能”,相當于to be very likely to
“may as well或might(just)as well+動詞原形”意為“最好,滿可以,倒不如”,相當于“had better或there is no reason to do anything else. 1． It may well change forever the way you look at Greek art.
2． There may well be a real problem here.
3． There is nothing to do, so I may as well go to bed.
4． You may as well tell us now, we’ll find out sooner or later.
5． I suppose we might as well go home.
6． And if you have to plough the field anyway, you might as well plant it at the same time.
二．must和have to
情態(tài)動詞 用法 例句
must 表示“必須,應該”之意,語氣比should,ought to強烈.其否定形式mustn’t表示“不準,不應該,禁止”等意 1． You must come to school on time.
2． Everybody must obey the law.
3． You mustn’t drive so fast in the street.
4． We mustn’t waste any more time.
在回答帶有must的問句時,否定回答常用needn’t或don’t have to,表示“不必”,而不用mustn’t 1．—Must I come back before ten?
—Yes,you must.(No, you needn’t)
表示有把握的推測,意為“一定、準是、相必”,只用于肯定句中 1． It must be my mother.
2． You must be hungry after a walk.
3． There must be a hole in the wall.
have to
have to “必須,不得不”,意義與must相近.但must表示的是說話人的主觀看法,而have to則往往強調(diào)客觀需要. 1． The film is not interesting. I really must go now.
2． I have to go now, because my mother is in hospital.
must只有一種形式,即現(xiàn)在式與過去式都是一種形式,而have to則涉及各種人稱、時態(tài)等方面的變化形式. 1．I had to work hard when I was your age.
2．I will have to learn how to use a computer.
3．In order to take the exam, we’ll have to finish the whole book by the end of this month .
兩者的否定意義不同,mustn’t表示“禁止,不許”,don’t have to表示不必. 1． You mustn’t go there.
2． You don’t have to go there.
四．shall和should
情態(tài)動詞 用法 例句
shall 用于第一、二、三人稱構成的疑問句,表示征求對方意見或請求指示 1． Shall I open the window?
2． Shall we say 6 o’clock, then?
3． What shall I get for dinner?
用于第二、三人稱陳述句中,表示說話人給對方的命令、警告、允諾或威脅. 1． Don’t worry, you shall get the answer this afternoon.(允諾)
2． He shall be sorry for it one day, I tell you. （警告）
3． You shall do as I say. (命令)
4． If you children don’t do as I tell you, you shall not go to the party. (威脅)
should 表示勸告或建議,意為“應該” 1． What should I do?
2． Should I trust him?
3． You should read his new book.
表示推測,用在肯定句中,對現(xiàn)在的情況或可能發(fā)生
的事的主觀推測或期待.意為“想必,大概,或許” 1． It should be a nice day tomorrow.
2． Try phoning Robert, he should be home now.
3． He should be around sixty years old.
還可以用在if引導的條件句中,表示一件事聽起來可能性很小,但也不是完全不可能,相當于“萬一”的意思.從句謂語用should+動詞原形構成,主句都一定用虛擬語氣 1． Ask Tom to ring me up if you should see him. (你萬一見到湯姆,請讓他給我打個電話)
2． Should I be free tomorrow, I’ll come. (萬一我明天有時間,我就過來)
3． If things should change suddenly, please let me know. (萬一情況突變,請通知我)
用于疑問句或感嘆句中,表示意外、驚異的情緒,意為“竟會”,與why,what,how,who連用,如果是疑問句,則不需要回答. 1． Why should anyone want to marry Tony?
2． Don’t ask me. How should I know?
五．will和would
情態(tài)動詞 用法 例句
will/would 用于表示意志或意愿.will指現(xiàn)在,would指過去. 1． He is the man who will go his own way. (他首歌自行其是的人.)
2． They said they would meet us at 10:30 at the station.
表示請求、建議等,用would比用will委婉、客氣. 1． Will you please take a message for him?
2． Would you please tell me your telephone number?
表示習慣或傾向,意為“總是,慣于”.will至現(xiàn)在,would指過去. 1． Fish will die without water.
2． People will talk. (人們總會說閑話.)
3． When we worked in the same office, we would often have coffee together.
表示推測,意為“很可能,大概”.will表示推測比should把握大,比must把握小. 1． These things will happen.
2． That will be the messenger ringing.
3． It would be about ten o’clock when he left home.
表示功能,意為“能,行”.慣用形式：will do/would do表示“解決問題”、“就行”. 1． That will be all right.
2． Either pen will do.
3． It would not do to work too late.（工作太晚不行.）
用于否定句中,意為“不肯”、“不樂意” 1．I won’t listen to your nonsense.
2．No matter what I said, he wouldn’t listen to me.
特別說明：would與used to辨析
would可用來表示過去反復出現(xiàn)的動作,但不能表示過去存在的狀態(tài),所以我們不能說：“she would be a quiet girl.”
另外,would強調(diào)過去某種特定情況下的活動,是完全過去的事情,同現(xiàn)在沒有聯(lián)系.而used to則著眼于過去和現(xiàn)在的對比,隱含現(xiàn)在已不存在,動作或狀態(tài)都可表示.Would可以表示不規(guī)則的習慣,used to則不可.如：
He used to be a naughty boy and cause trouble.
I used to get up at six in the morning.
Sometimes she would take a walk in the neighboring woods.
In those days, whenever I had difficulties, I would go to Mr. Chen for help.
六．need和dare
情態(tài)動詞 用法 例句
need 用于表示“需要,必要”之意.做情態(tài)動詞時,僅用于否定句和疑問句,只有現(xiàn)在時,過去式要用needn't have,疑問式用need+人稱?,否定式用need not(即needn't）, 1．—Need we leave soon?
—Yes, you must.(No, you needn't)
2．You needn't have hurried.
(=It was not necessary for you to hurry,but you did).你當時不必這么匆忙.
做實義動詞時,其變化與一般的實義動詞相同,后接帶to的不定式（need doing = need to be done ）,過去式用needed、did you need?和didn't need,肯定式用needs/needed/need,疑問式用do、does、did提問,否定式要在前面加don't、doesn't、didn't 1. A job like nursing needs patience and understanding.(need+名詞,need understanding=need to be understood,需要被理解)
2．He needs to see a doctor.(need to do)
3．Do you still need volunteers to help clean up after the party?(needsomebody to do something)
4．They didn't need to start so early.(do not need to do)
dare 用于表示“敢于”之意.做情態(tài)動詞,沒有人稱和數(shù)的變化,主要用于否定句、疑問句和條件狀語從句中 1．—Dare you tell her the truth?
—Yes, I dare. /No, I daren’t.
3． How dare you accuse me of lying!
4． He daren’t admit this.
用作實義動詞時,其變化與一般的實義動詞相同.在肯定句中,dare后接帶to的不定式；否定句中,dare后既可接帶to的不定式,也可接不帶to的不定式. 1． Only a few journalists dared to cover the story.
2． He doesn’t dare (to) go there alone.
3． Don’t you dare (to) touch it?
七．ought的用法：
情態(tài)動詞 用法 例句
ought to do 表示“應該”之意 1． You ought to take care of him.
2． —Ought I go now?
—Yes, you ought to. /No, you oughtn’t to.
表示推測.注意與must表示推測是的區(qū)別 1． He must be home by now. (斷定他已到家)
2． He ought to be home by now. (不十分肯定)
3． This is where the oil must be. (比較直率)
4． This is where the oil ought to be. (比較含蓄)
說明：should與ought to 表示“應該”時的區(qū)別
should 表示自己的主觀看法,而ought to的語氣中,含有“按道理應該……”之意.若要反映客觀情況或涉及法律義務和規(guī)定,一般用ought to.如：
You should help them with their work.
You are his father. You ought to get him to receive good education.
八．“情態(tài)動詞+have done”用法
情態(tài)動詞+have done 用法 例句
must have done表示主觀上對過去已經(jīng)發(fā)生的行為進行推測,意為“想必,準是,一定做了某事” 1． She must have gone through a lot.
2． He must have visited the White House during his stay in the United States.
may/might have done 表示對過去已發(fā)生行為的推測,意為“也許/或許已經(jīng)（沒有）……“.一般用于肯定句或否定句中,不用于疑問句.用might則表示語氣更加不肯定. 1． You may have learnt the news.
2． He may not have heard his name called.
3． Sorry I’m late. I might have turned off the alarm clock and gone back to sleep again.
can…h(huán)ave done
cannot have done 表示對過去發(fā)生的行為的懷疑和不肯定,通常用在否定句和疑問句中.（can換成could時語氣委婉） 1． Where can she have gone?
2． Could he have done such a foolish thing?
3． The boy can’t have finished reading the book so soon because it is difficult even to an adult.
could have done 可用于肯定句中,表示“可能已經(jīng)……”之意,此外,還可以表示過去能做而沒做的事,有一種對過去為付諸實施的事情的惋惜. 1． He could have killed himself driving at a dangerous speed.
2． You could have been more considerate.
3． You could have done better, but you were too careless.
might have done 表示“本來可能……,但實際上沒有發(fā)生的事情”.另外,還可以表示“本來應該或可以做某事”之意,含有輕微的責備語氣. 1． You should not swim in that sea. You might have been eaten by a shark.
2． He might have given him more help, thought he was busy.
should/ought to have done 用于肯定句時,表示本該做某事,而實際上未做；用于否定句時,則表示不該做的事反而做了. 1． He should have known that the police would never allow this sort of thing.
2． You shouldn’t have done it so carelessly.
3． You ought to have returned the book earlier.
4． You ought not to have refused his offer.
needn’t have done 表示做了本來不必去做的事.注意：didn’t need to do表示“沒必要做而實際上也沒有做某事” 1． You needn’t have watered the plants, for it is going to rain.
2． I didn’t need to buy the dictionary. I had a copy at home.
had better have done 用于事后的建議,含輕微責備的口吻,意為“當時最好做了某事”,其否定式had better not have done表示相反的含義. 1． You had better have started earlier.
2． You had better not have scolded her.
would rather have done 表示“當時寧愿做了某事”,其否定式would rather not have done表示相反的含義,兩者都表示“后悔”之意. 1．I would rather have taken his advice.
2．I would rather not have told him the truth.