1. can (could)
1）表示能力,could主要指過(guò)去時(shí)間.
Two eyes can see more than one. 兩只眼比一只眼看得清.
Could the girl read before she went to school? 這女孩上學(xué)前能識(shí)字嗎?
2）表示可能（理論上或是邏輯判斷上）.
The temperature can fall to –60℃, that is 60℃ below freezing.
氣溫可降至—60℃,也就是零下60℃.
He can´t (couldn´t) have enough money for a new car. 他不可能有足夠的錢買新車.
You mustn´t smoke while you´re walking around in the wood. You could start a fire.
在林子里走時(shí)勿吸煙,那樣可能會(huì)引起火災(zāi).
3）表示允許.
Can I have a look at your new pen? 我可以看一看你的新鋼筆嗎?
He asked whether he could take the book out of the reading—room.
他問(wèn)他可不可以把書帶出閱覽室.
4）表驚異、懷疑、不相信等態(tài)度.主要用于否定句、疑問(wèn)句或感嘆句中.
Where can (could) they have gone to? 他們會(huì)去哪兒了呢?
He can´t (couldn´t) be over sixty. 他不可能超過(guò)六十歲.
How can you be so careless? 你怎么這么粗心?
5）比較委婉客氣地提出問(wèn)題或陳述看法.
Can (Could) you lend me a hand? 幫我一把好嗎?
I´m afraid we couldn´t give you an answer today. 恐怕我們今天不能給你答復(fù).
2. may (might)
1）表允許,might可以指過(guò)去時(shí)間,也可指現(xiàn)在時(shí)間,語(yǔ)氣更委婉.
You may take whatever you like. 你喜歡什么就拿什么.
He told me that I might smoke in the room. 他告訴我可以在房間里抽煙.
May (Might) I ask for a photo of your baby? 我可以要一張你寶寶的照片嗎?
在回答以may引起的問(wèn)句時(shí),多避免用這個(gè)詞,而用其它方式,如Yes, please. / Certainly.
/ Please don´t ./ You´d better not. / No, you mustn´t.等,以免顯得太嚴(yán)峻或不客氣.
2）表可能（事實(shí)上）.可以指過(guò)去時(shí)間,也可以指現(xiàn)在時(shí)間,但語(yǔ)氣更加不肯定.
He may be at home. 他可能在家.
She may not know about it. 她可能不知道這件事.
He was afraid they might not agree with him. 他擔(dān)心他們可能不同意他的意見.
They might be having a meeting, but I´m not sure. 他們有可能在開會(huì),不過(guò)我不肯定.
3. must
1）表示義務(wù).意為“必須”（主觀意志）.
We must do everything step by step. 我們一切都必須循序漸進(jìn)地做.
You mustn´t talk to her like that. 你不可能那樣對(duì)她說(shuō)話.
--Must we hand in our exercise—books now? 我們現(xiàn)在就要交練習(xí)本嗎?
--No, you needn´t. / No, you don´t have to. 不必.（這種情況下,一般不用mustn´t）
2）表示揣測(cè).意為“想必、準(zhǔn)是、一定”等,只用于肯定句.
He must be ill. He looks so pale. 他準(zhǔn)是病了.他的臉色蒼白.
She´s wearing a diamond necklace. She must have a lot of money. 她戴著鉆石項(xiàng)鏈,一定很有錢.
4. shall
1）表征詢意見,用于第一、第三人稱疑問(wèn)句.
Shall I get you some tea? 我給你點(diǎn)茶好嗎?
Shall the boy wait outside? 讓那男孩在外面等嗎?
What shall we do this evening? 我們今晚做什么?
2）表說(shuō)話人的意愿,有“命令、允諾、警告、決心”等意思,用于第二、第三人稱陳述句.
You shall do as I say. 按我說(shuō)的做.（命令）
You shall have my answer tomorrow. 你明天可以得到我的答復(fù).（允諾）
He shall be sorry for it one day, I tell you. 有一天他會(huì)后悔的,我告訴你.（警告）
Nothing shall stop us from carrying out the plan. 什么也不能阻止我們執(zhí)行這項(xiàng)計(jì)劃.（決心）
5. will
1）表意愿,用于各種人稱陳述句.
I will do anything for you. 我愿為你做任何事.
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. 如果你愿意讀這本書,我會(huì)把它借給你.
2）表請(qǐng)求,用于疑問(wèn)句.
Will you close the window? It´s a bit cold. 請(qǐng)你把窗戶關(guān)上好嗎?有點(diǎn)冷.
Won´t you drink some more coffee? 再來(lái)一點(diǎn)咖啡好嗎?
3）表示某種傾向或習(xí)慣性動(dòng)作.
Fish will die out of water. 魚離開水就不能活.
The door won´t open. 這門打不開.
The boy will sit there hour after hour looking at the traffic go by.
那男孩常常坐在那里好幾個(gè)鐘點(diǎn),看著車輛行人通過(guò).
6. should
1）表義務(wù).意為“應(yīng)該”（某件事宜于做）,用于各種人稱.
You should be polite to your teachers. 你對(duì)老師應(yīng)該有禮貌.
You shouldn´t waste any time. 你不應(yīng)該浪費(fèi)時(shí)間.
2）表推測(cè),意為“想必一定、照說(shuō)應(yīng)該、估計(jì)”等.
The film should be very good as it is starring first—class actors.
這部新電影是一流演員主演的,估計(jì)拍得很好.
They should be home by now. 照說(shuō)他們現(xiàn)在應(yīng)當(dāng)已經(jīng)到家了.
7.would
1）表意愿.
They would not let him in because he was poorly dressed. 他們不讓他進(jìn)去因?yàn)樗轮婆f.
I said I would do anything for you. 我說(shuō)過(guò)我愿意為你做任何事.
2）表委婉地提出請(qǐng)求、建議或看法.
Would you like another glass of beer? 再來(lái)杯啤酒好嗎?
Would you mind cleaning the window? 請(qǐng)把窗戶擦一下好嗎?
They wouldn´t have anything against it. 他們不會(huì)有什么反對(duì)意見.
3）表過(guò)去反復(fù)發(fā)生的動(dòng)作或過(guò)去的一種傾向.
Every time she was in trouble, she would go to him for help.
她每遇到麻煩都會(huì)向她求助.他告訴我盒子打不開了.
（二）情態(tài)動(dòng)詞后跟完成式和進(jìn)行式的用法
1.情態(tài)動(dòng)詞后跟完成式,表“應(yīng)當(dāng)已經(jīng)……”,“想必已經(jīng)……”,“本來(lái)可以……”等意.
I should have finished the work earlier. 我應(yīng)當(dāng)早一點(diǎn)完成這項(xiàng)工作的.
He isn´t here. He must have missed the train. 他還未到,一定是沒(méi)趕上火車.
Where can (could) he have gone? 他能到那里去了呢?
You may (might) have read about it. 你可能在報(bào)上已經(jīng)讀到這件事了.
You could (might) have been more careful. 你本來(lái)可以更細(xì)心的.
He needn´t have worried about it. 他本不必為此事?lián)?
There was a lot of fun at yesterday´s party. You ought to have come, but why didn´t you?
昨天的聚會(huì)非常有意思.你本應(yīng)該來(lái),為何不來(lái)呢?
2. 情態(tài)動(dòng)詞后跟進(jìn)行式,表示“想必正在……”,“可能正在……”,“應(yīng)當(dāng)正在”等意.
It´s twelve o´clock. They must be having lunch. 現(xiàn)在是十二點(diǎn).他們一定正在吃飯.
They may be discussing this problem. 他們可能正在論討這個(gè)問(wèn)題.
He can´t be telling the truth. 他說(shuō)的不可能是真話.
She shouldn´t be working like that. She´s still so weak. 她不應(yīng)當(dāng)那樣干,她身體仍那么虛.
（三）幾組詞的辨異
1. can 和be able to
1）情態(tài)動(dòng)詞can只有兩種時(shí)態(tài)形式,現(xiàn)在式can和過(guò)去式could,而be able to有多種時(shí)態(tài)形式.
Mary can play the piano. She has been able to play it since she was 5.
瑪麗會(huì)彈鋼琴.她五歲起就會(huì)彈了.
2）用在過(guò)去時(shí)中,could經(jīng)常表示能夠做某事,事實(shí)上不一定去做,而was∕were able to則表示“過(guò)去做成了某事”.在否定句中兩者可通用.
He could swim across the English Channel. But he didn´t feel like it that day.
他能游過(guò)英吉利海峽,但那天他不想游.
Yesterday I was able to get home before the heavy rain. 昨天我在下大雨前趕到了家里.
2. must和 have to
must表示主觀意志,而have to表示由于客觀因素不得不做某事.must沒(méi)有過(guò)去式,除在間接引語(yǔ)中可用于表示過(guò)去時(shí)間,在直接引語(yǔ)中表示過(guò)去時(shí)間應(yīng)該用had to代替.
I told her that she must give up smoking. 我叫她必須戒煙.
We had to get everything ready that night. 我們那晚得把一切準(zhǔn)備就緒.
3. would和used to
1）used to表示過(guò)去與現(xiàn)在或過(guò)去某時(shí)與后來(lái)的情況有不同,而would只表過(guò)去的情況.
People used to think that the earth was flat.
過(guò)去人們認(rèn)為地球是平的.（現(xiàn)在人們不這么認(rèn)為.）
She would go out for a walk in the morning when she was in the country.
在鄉(xiāng)下時(shí),她總是在早晨去散會(huì)兒步.（可能現(xiàn)在仍有散步的習(xí)慣.）
2）used to可表示過(guò)去的習(xí)慣動(dòng)作和經(jīng)常的情況,而would只表示過(guò)去的習(xí)慣動(dòng)作.
He used to ∕would smoke while writing. 過(guò)去他寫東西時(shí)常抽煙.
She used to be fat. 她過(guò)去很胖