英語中有一種特殊動詞,其本身不能單獨作謂語,只能和句子中的實義動詞一起構(gòu)成謂語。這種特殊的動詞就是助動詞。
情態(tài)動詞是一種比較特殊的助動詞,本身具有特殊的含義,常常表達命令、義務(wù)、揣測等意義。
情態(tài)動詞是表示說話人的語氣或情態(tài)的動詞。情態(tài)動詞本身有詞義,但不能單獨作謂語,在句中必須跟動詞原形,并與后面的動詞原形一起構(gòu)成謂語。情態(tài)動詞沒有人稱和數(shù)的變化。常用的情態(tài)動詞有:can,may,must,could,might,will,shall,would,should,need等。
1.情態(tài)動can,could的4種用法
(1)表示能力,指過去、現(xiàn)在無論什么時候想做就能做到的能力,意為 “能,會”。could是can的過去式,can表示現(xiàn)在的能力;could表示過去的能力。如:
I can sing this song in English.我能用英語唱這首歌。
Can you tell me where the museum is?你能告訴我博物館在哪嗎?
I couldn't play the piano until I was five years old.我直到五歲才會彈鋼琴。
注意:
can與be able to都表示“能;能夠”,但它們在用法上有區(qū)別:
①be able to 強調(diào)通過努力而獲得的能力,而can則強調(diào)自身已具有的能力。如:
Hens can hatch chickens.母雞能孵小雞。
I'm sure he will be able to work out the problem.我肯定他能算出那道題。
②be able to 強調(diào)一種結(jié)果,而can只強調(diào)一種可能。如:
Luckily,he was able to escape from the big fire in the end.幸運的是,他終于逃出了大火。
If he got here a few hours earlier,I could save him.要是他早幾小時來,我還能救他。
③be able to 可以有各種時態(tài);而can只有一般現(xiàn)在時和一般過去時兩種時態(tài)。如:
I could help you last night,but you didn't come.昨天晚上我能幫你,而你又沒來。
Can you see it there?你能看見它在那兒嗎?
He is/was/will be able to help you.他能幫你的忙。
④can可用于表示可能性,推測,允許等情況,而be able to通常不這樣用。如:
Somebody is knocking at the door.Who can it be?有人在敲門,會是誰呢?
It can't be our teacher who is knocking at the door.正在敲門的那個人不可能是我們的老師。
(2)表示請求和許可,意為 “可以”,此時可以與may互換使用。如:
You can use my pen instead 你可以用我的筆。
Can I come in?我可以進來嗎?
Could I watch TV for a while,Mum?媽媽,我可以看一會兒電視嗎?
注意:
①用could表示請求時,could不是過去式,而是表達一種客氣委婉的語氣。如:
Could I have the television on?我可以開電視嗎?
②表示允許別人做某事時只能用can,不能用could。如:
— Could I use your mobile phone for a while?我可以用一會兒你的手機嗎?
— Yes,of course you can.好的,當(dāng)然可以。
— Could you answer me a question?請回答我一個問題好嗎?
— Yes,I can./No,I can't.好。/不行。
(3)表示肯定推測,意為 “可能,會”,但只表示一種猜測或者是理論上的可能性;表示否定推測,can't意為“不可能;不會”。如:
Can he be there too?他也會在那兒嗎?
Even experienced teachers can make mistakes.即使是有經(jīng)驗的教師也可能出錯。
He can't have finished his work.他不可能把工作做完了。
(4)表示驚訝,通常用于疑問句、否定句和感嘆句中。如:
Can this be your reason?這難道就是你的理由?
How can you say it like that?你怎么能那樣說話呢?
2.情態(tài)動詞may,might的用法
(1)表示請求和許可,意為“可以”,比can和could更正式。might含有試探和猶豫不決的意思。表示給予許可時,用may不用might;may not用來表示拒絕或禁止。如:
May/Might/Can I come in?我可以進來嗎?
He said I might borrow his car.他說我可以借他的車。
You may take everything you like.你喜歡什么就拿什么吧。
You may not go out at night.晚上你不可以出去。
注意:
①might是may的過去式。但上述第一例中的might不是過去式,而是表示客氣委婉的語氣;第二例中主句用了過去時,賓語從句中的might可視為過去式。
②might除用作may的過去式外,還可表示現(xiàn)在,但語氣比may更委婉。如:
Might I have a look at your new computer?我可以看一看你的新電腦嗎?
You might tell us the truth.你不妨把真相告訴我們。
③若用might代替may提出請求,注意其答語不能再用might。如:
— Might I ask you a question?我可以問你個問題嗎?
— Yes,you may./No,you can't.—可以。/不可以。
(2)表示推測,通常用于肯定句和否定句中,意為“可能”。如:
He may be very busy now.他現(xiàn)在可能很忙。
Peter might phone.If he does,could you ask him to ring later?彼得可能會打電話。如果他打電話的話,能否告訴他晚些時候再打過來?
He said that she might not be at work today.他說她今天可能不上班。
注意:
①表示推測時,might一般不表示過去式,而是表示客氣委婉的語氣。
②can和may都可表示推測,can通常用于否定句和疑問句,而may 則通常用于肯定句和否定句。雖然兩者均可用于否定句,但其意思不同:can't 意為“不可能”,may not意為“可能不”,后者較前者語氣弱得多。如:
It can't be true.那不可能是真的。
It may not be true.那可能不是真的。
③can和may 均可表示請求允許,但can 為一般用詞,而may為正式用語。
3.情態(tài)動詞must與have to的使用4注意
(1)must表示主觀義務(wù),意為“必須”,其否定式must not可縮寫為mustn't,意為“不能,不準(zhǔn)”。如:
We must get there before five o'clock.我們必須在五點鐘前趕到那兒。
You mustn't break the rules.你不能破壞規(guī)定。
注意:
must開頭的一般疑問句否定回答用needn't或don't have to,意為“不必”。如:
Must I stay here after school?放學(xué)后我還必須留在這兒嗎?
No,you needn't/don't have to.不了,沒有必要。
(2)must表示推測、推斷,只用于肯定句中,意為“一定,必定”。如:
He must be our headmaster.他一定是我們的校長。
They are friends.He must know about him.他們是朋友,他一定了解他。
He must have seen the film last night.他昨天晚上一定看了那場電影。
注意:
①must只表示肯定推測,表示否定推測用can't。如:
The light is still on,so he must be at home.燈還亮著,所以他一定在家。
The man can't be my father.He went to Beijing early this morning.那人不可能是我父親,他今天一早就去北京了。
②對目前的情況進行推斷用must+動詞原形;對過去的事情進行推斷用must have+過去分詞。如:
The light was out.They must have gone to bed.燈都熄了,他們一定是睡了。
(3)have to表示客觀要求,意為“不得不;必須;得”。如:
Now there's no bus here,so we have to walk home.現(xiàn)在這里沒有公共汽車了,我們不得不步行回家。
We have no food at home,you have to go and get some,Tom.家里沒有食物了,湯姆你得去買一些來。
(4)have to可以用于多種時態(tài);而must只用于一般現(xiàn)在時態(tài)。如:
I had to get up early yesterday.昨天我必須很早起床。
You will have to be here on time next Monday.下周一你必須按時來這兒。
4.情態(tài)動詞need的用法
need作情態(tài)動詞,其后用動詞原形,只用于否定句和疑問句中。在疑問句中need意為“需要”;在否定句中,need與not可縮寫為needn't,意為“不必”。如:
You needn't go there yourself.你不必自己親自去那兒。
Need I help you do the housework?我需要幫你干家務(wù)活嗎?
注意:
①need一般疑問句的肯定回答用must,否定回答用needn't。如:
— Need I do anything for you?我需要為你干些什么嗎?
— Yes,you must.是的,你得做。
— No,you needn't.不,沒有必要。
②need還可用作實義動詞,意為“需要”,這時need有人稱、數(shù)及時態(tài)的變化,它可接名詞,代詞,動詞不定式及動詞的-ing形式作賓語。接動詞-ing形式作賓語時,它的主動形式表被動意義。如:
He needs help.他需要幫助。
Does he need help?他需要幫助嗎?
He doesn't need help.他不需要幫助。
The house needs cleaning.房子需要打掃。
The house needs to be cleaned.房子需要打掃。
5.情態(tài)動詞will與would的用法
(1)will和would作情態(tài)動詞表示意愿。will 表示現(xiàn)在的意愿,would表示過去的意愿。如:I will pay you at the rate you ask.我愿意照你要求的價錢付款。
Go where you will.你愿到哪里就到哪里。
He wouldn't help me yesterday.他昨天不愿幫助我。
She asked if I would go with them.她問我是否愿意同他們一起去。
注意:
would也可表示現(xiàn)在的意愿,但語氣較will委婉。如:
I would go there with you.我愿同你一起去那兒。
I wouldn't go.我不愿意去。
(2)表示征求意見或提出請求,主要用于第二人稱的疑問句中,will和would均可用,would此時并不表過去,而表示委婉語氣。如:
Won't you take off your coat?你要不要把大衣脫掉?
Will/Would you please post the letter for me?請幫我寄了這封信好嗎?
Would Sunday night suit you?星期天晚上適合你嗎?
注意:
would有時用于提出想法,通常與like,love,hate,prefer,be glad,be happy等連用,若用于第一人稱有時也可將would換成should。如:
I'd like/love to have a look at it.我想看看它。
I would prefer not to go out today.我今天不想出去。
(3)表示習(xí)慣和傾向性。will表示現(xiàn)在的習(xí)慣,would表示過去的習(xí)慣。如:
Oil will float on water.油總是浮在水上。
This window won't open.這扇窗戶經(jīng)常打不開。
When he was a child,he would often go skiing.他小時候經(jīng)常去滑雪。
(4)表示推測。will用于談?wù)摤F(xiàn)在,would可用于談?wù)撨^去,也可用于談?wù)摤F(xiàn)在,但語氣較will更委婉。如:
This car will hold six people.這輛小汽車可以坐六個人。
Ask him.He will know.問問他吧,他大概知道。
You wouldn't know.你不會知道。
Every family would have some sort of trouble.家家都會有本難念的經(jīng)。
The person you mentioned would be her father,is that right?你提的那個人想必是她的父親,對嗎?
6.情態(tài)動詞shall的用法
(1)shall在疑問句中用來征求對方意見,主要用于第一人稱,在英國英語中,也用于第三人稱,意為“要不要;……好嗎”。如:
Shall we meet again tonight?咱們今晚再見面好嗎?
Shall they wait for you?要不要他們等你?
(2)shall在陳述句中表示說話者的允諾、告誡、威脅、命令、必然性等,主要用于第二、三人稱。如:
You shall suffer for this.你會為此事吃苦頭的。(表示威脅)
That day shall come.那一天一定會來。(表示必然性)
You shall hear everything directly you come.你一來就可聽到所有情況了。(表示允諾)
注意:
①Shall I...?用來詢問對方的意見。其肯定回答為:Yes,please./Yes,do it,please.否定回答為:No,please don't./Sorry,……如:
— Shall I leave the window open?我可以開著窗嗎?
— Yes,please.好的,可以。/Sorry,I feel a little cold.對不起,我感覺有點冷。
②Shall we ...?是向?qū)Ψ教岢鼋ㄗh。其肯定回答為:All right./Yes.Yes,let's....其否定回答為:Sorry,I'm afraid we can't./No,let's not.如:
— Shall we start off now?我們現(xiàn)在可以開始了嗎?
— Yes,let's start.好的,我們開始吧。/Sorry,Lucy hasn't turned up yet.對不起,露西還沒來呢。
7.情態(tài)動詞should的用法
(1)表示義務(wù)、責(zé)任等,意為“應(yīng)該,應(yīng)當(dāng)”。否定句should not可縮寫為shouldn't。如:
He should work harder.他應(yīng)該更加努力工作。
You should help your mother with the housework.你應(yīng)該幫你母親做家務(wù)。
You shouldn't leave your little brother at home by himself.你不應(yīng)當(dāng)把你的小弟弟單獨留在家里。
(2)表示可能性,意為“可能;該;按道理來說”。如:
He should arrive soon他可能很快就到了。
The train should have already left.火車大概已經(jīng)走了。
(3)should的完成式:should have done表示“本應(yīng)該做某事,但事實上卻沒有做”;shouldn't have done表示“本不該做某事,但事實上卻做了”。如:
You should have got up earlier.你本應(yīng)該早點起的。
You shouldn't have told him about it.你本不該把這件事告訴他的。
[辨析] should與ought to
①情態(tài)動詞should與ought to都表示“應(yīng)當(dāng);應(yīng)該;可能”等,兩者可互換,只是ought to的語氣稍重。如:
You ought to/should work harder than that.你應(yīng)當(dāng)更努力地工作。
She ought to/should finish it by next week.下星期她可能完成了。
You ought to/should have told him about it earlier.你本應(yīng)該早點把這件事告訴他的。
You oughtn't to/shouldn't have wasted time like that.你本不該像那樣浪費時間的。
②should 強調(diào)主觀看法,而 ought to 強調(diào)客觀要求。如:
It should be ten o'clock now.現(xiàn)在該有十點了。
We ought to go and see my mother in hospital tomorrow,but I don't think we will.我們按理應(yīng)當(dāng)在明天去看看住院的母親的,但我認為我們不會去。
③在公告、須知或條例中,出于禮貌,常用should而不用ought to。如:
You shouldn't run alongside the swimming pool.不準(zhǔn)在游泳池邊奔跑。
④在虛擬語氣中只能用should不用ought to。如:
He suggested that I should go there.他建議我去那里。
⑤ought to的否定式是ought not to;疑問式是Ought+主語+to do;反意疑問式是oughtn't+代詞主格。如:
You ought not to do it.你不應(yīng)該做此事。
— Ought he to start now?他現(xiàn)在該動身了嗎?
— Yes,he ought (to).是的,該動身了。
They ought to go now,oughtn't they?他們現(xiàn)在該走了,對嗎?
【中考速遞】
1.[上海中考考題] A good friend is someone you _____ share your pleasure and pain with.
A.ought B.need C.can D.must
2.[河南中考考題] — You look very pretty,if I _____ say so.
— Thanks a lot for saying that.
A.must B.may C.will D.have to
3.[海南中考考題] — Must I clean the room now?
— No,you _____.You can do it later.
A.needn't B.can't C.may not
4.[遼寧丹東中考考題] — Please be quiet.Our teacher is coming.
— It _____ be our teacher.She has gone to Beijing.
A.must B.may C.can't D.mustn't
5.[江西中考考題] You _____ take me to the station.My brother's taking me.
A.can't B.mustn't C.shouldn't D.don' t have to
6.[湖南長沙中考考題] — Finally,they came back.
— They _____ be hungry after such a long walk.
A.can't B.must C.needn't
【答案點撥】
1.答案:C 句意:真正的好朋友是可以分享快樂和痛苦的人。表示“可以”用情態(tài)動詞can,故選C。
2.答案:B 句意:“你看上去很漂亮,我是否可以這樣說?!薄岸嘀x夸獎?!北硎菊埱笤S可用情態(tài)動詞may,故選B。
3.答案:A 句意:“我必須現(xiàn)在打掃房間嗎?”“不,你不必。你可以過一會兒打掃。”must引導(dǎo)的一般疑問句否定回答用needn't表示“不必”,故選A。
4.答案:C 句意:“請安靜。我們的老師來了?!薄安豢赡苁俏覀兝蠋煛K奖本┤チ?。”表示否定推測用can't表示不可能,故選C。
5.答案:D 句意:你不必帶我去車站了。我兄弟要帶我去。由下句可推知這里為沒有必要,故選D。
6.答案:B 句意:“最終,他們回來了”“走了這么長的一段路,他們一定餓了?!庇蒩fter such a long walk可推知這里用must be“一定是”表示肯定推測,故選B。
【語法專練 體驗中考】
1.[遼寧大連] We need clear air and water,so we _____ protect the environment.
A.can B.may C.must D.might
2.[黑龍江哈爾濱] — Hi,Jack!Could you come to our English party?
— Sorry,I _____.I have to look after my little sister at home.
A.must B.could C.can't
3.[山東濟南] — Helen,who _____ fix up the computer in our class?
— I think Jeff can.
A.should B.would C.must D.can
4.[湖北隨州] — Let's go climbing,shall we?
— You _____ be joking!Don't you know I'm afraid of high places?
A.must B.can C.may D.should
5.[遼寧沈陽] — What should we do to protect the fish in the river?
— We _____ throw rubbish into the river.
A.need B.needn't C.must D.mustn't
6.[青海考題] — Look!Is that your brother Johnson?
— Oh,it _____ be him.He is in London now.
A.can't B.must C.mustn't
7.[廣東考題] — Mum,_____ I visit the Modern Art Museum next Monday.
— I am afraid you can't.All the museums in this city are closed on Monday.
A.would B.need C.should D.may
8.[新疆考題] — Must I do the dishes now?
— No,you _____.
A.mustn't B.needn't C.may not D.can't
9.[山西考題] — Many people play with mobile phones all day instead of reading books.
— That's too bad.Everyone _____ be a book lover.Reading is more enjoyable.
A.may B.should C.would
10.[江蘇泰州] — Could I smoke here?
— Sorry.I am afraid you _____.Look at the sign “No smoking”!
A.couldn't B.needn't C.can't D.won't
11.[天津考題] — Mum,_____ I play football this afternoon?
— Sure,but you _____ finish your homework first.
A.may;could B.can;must C.can;mustn't D.may;can't
12.[湖北武漢] — I still haven't found my pet dog.
— I'm sorry to hear that.You _____ be very sad.
A.can B.should C.must D.will
13.[甘肅白銀] — Excuse me,is this the right way to the Children's Palace?
— Sorry,I'm not sure.But it _____ be.
A.mustn't B.might C.can't D.must
14.[四川內(nèi)江] — Look,the lady in red _____ be our English teacher.
— No,she _____ be.She is in the office now.
A.must;can't B.can;mustn't
C.may;mustn't D.shall;can't
15.[重慶考題] — Must we finish the work today?
— _____.We have something else to do tomorrow.
A.Yes,we can B.No,we can't.
C.Yes,we must. D.No,we needn't
【答案速遞】
1.C 2.C 3.D 4.A 5.D 6.A 7.D 8.B 9.B 10.C 11.B 12.C 13.B 14.A 15.C
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