(整理版高中英语)十一情态动词
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十一. 情 态 动 词
情态动词表示说话人的语气和情态。如需要、可能、愿意、疑心等。情态动词有一定的词义，但不完整，必须和主要动词的原型一起构成谓语。常用的情态动词有：can, could, may, might,
must, have to, ought to, need, dare, shall,
will, should, would, be able to,及半情态动词be to do, had better等。
情态动词的根本用法：
〔一〕can“能够〞
1.表示体力或脑力方面的能力，或根据客观规律能做某事的能力。如：
He can speak English. I can go there now.
注意
(1)can表“能够〞时，既可指现在也可指将来。
(2)can与be able to的区别：
① 表“能力〞时二者同义
No one can / is able to do it.
② be able to常侧重经过努力有能力做到，有多种时态。can侧重自身的能力，只有一般现在时和一般过去时。
③ was / were able to do表示通过努力克服困难或在一定的条件下成功地做了某事，侧重结果，相当于managed to do或succeeded in
doing...。could仅表自身的能力或本领，但未必成功做到。
With the help of the firemen, they were able
to leave the burning house.
He was able to swim across the river.
In the end, we were able to rescue the workers
trapped in the fire.
“许可，允许〞。在疑问句中表示请求，许可；否认句中表示“不许〞。此时常与may通用：
May/Can I do it?
This sort of thing can't go on! 这类事情不能再继续了！
注意 can not有时可以表示“禁止〞相当于mustn't：
You can't〔mustn't，are not allowed to〕play football in the street.你不可以在大街上踢球。
3.表示推测，强调客观可能性：“可能、会〞。主要用于疑问句和否认句。表示推测、估计时，后边可根据不同情况用动词原形、进行式、完成式。
Who can he be?
She can't be waiting for you.
He can't have gone there alone. 4.表惊讶、疑虑。
How can it be that he was late for the
opening ceremony?
他咋会连开幕式都迟到？
Can it be late? 会不会晚了？
〔二〕could
1．表“能力〞“可能性〞“许可〞，为can的过去式。
He said he could go.
2. could用于一般现在时中表委婉、客气地提出问题或陈述看法。〔此时不是can的过去式，要用can答复以显得爽快。此时can和could没有时间的差异，只是could语气更客气些。〕
-Could I borrow your pen?
- Yes, you can.
〔三〕may, might (may的过去式为might〕
1.表示许可，有“可以〞的意思，询问或说明一件事可不可以做，有时可以用can互换。
You may go now.
否认式may not表示“不可以、禁止、阻止〞等，常用must not〔＝mustn't〕代替。may用于疑问句中时，答复多防止用may，以免显得太严肃或不客气。
-May I watch TV tonight？
-Yes, you can.〔No, you mustn't/you'd better
not〕
-May I smoke here？
-Yes, please.(No, please don't.)
2.表推测：“或许、可能〞。表示一件事或许会发生，只用
在陈述句中。
It may rain tomorrow.
3. may可以表祝愿，一般放在句首构成倒装句式：
May you succeed! =I hope you may succeed.祝您成功!
May that day come soon! 希望这一天早日来到！
May you be happy, healthy and wealthy!
祝你快乐，健康，富有。
4. might是may的过去式，表可以做的事或可能发生的事。
She suggested a few books which I might buy.
5. might用于一般现在时比may委婉，或表示现实的可能性更小一些。
He might come soon.
I wonder if I might borrow some coffee？
6. may (just) as well, might as well.“不妨…〞〔可以用来提出建议〕。它们比had better显得谦逊或不那么有把握，所以had better通常是不用于长者或上司的。同时，had better有时带有威胁口吻。〔may well为“完全能；满可以；很可能〞，表示有可能或有充分理由做某事。well是may的程度副词〕
I needn't wait; I may as well tell you now.
我不必等，我不妨现在就告诉你。
Since it's a fine day, we might as well walk.
既然是好天气，我们一不妨走走。
You may well say so.你完全有理由这么说。
It may well be that the question is still
under discussion.
那很可能是该问题仍在讨论中。
●had better是固定词组，亦可说had best，用来表示一种很有把握的建议和劝告，意思是“最好…〞。
①现代英语中常用better代替had better, 有时省主语：
You had better be careful. = You better
be careful. = Better be careful.
②had better后接be doing结构时，表示立即做某事。
I think I'd better be going.我想我最好马上走。
③had better接完成式表示对过去本该做而没做的事的遗憾。
You'd better have come earlier.你本该早点来。
7. may, may not, might + be doing也表猜想，译为“可能，正在或可能不在干…〞
She may not be doing such silly things.
He may be doing his work.
〔四〕must
1.表示必须要做的事，意为“必须〞，否认式mustn't表示不准、不许、禁止等。在答复带有must的问句时，不用mustn't，而用needn't或don't have to。
I must go now.
We mustn't waste our time.
Must I go home? No，you needn't. / Yes, you
must.
2. must在表“必须〞时与have to相近，have to强调客观需要，must着重主观看法。另外must不像have to能有更多的时态。
You must be back by ten.〔命令或叮嘱〕
You have to be back by ten.〔客观需要〕
3.表推测，暗含很大的可能性，意为“一定、肯定〞，只用于“肯定句〞中。此时其否认式为can't,“绝非〞。
He must be over sixty. There must
be a mistake.
4.偏偏、硬要、干嘛〔指做令人不快的事〕
The car must break down just when we were
about to start off.
我们正要出发的时候偏偏车坏了。
Must you shout so loudly? 你干嘛这么大声喊？
〔五〕shall
1.表示命令、履行义务、意愿、许诺、警告、强制、威胁、决心等，一般用于二、三人称中，并用于陈述句。
You shall have my answer tomorrow.〔允诺〕
You shall be sorry for it one day, I tell
you.〔警告〕
You shall do as I tell you.〔命令或吩咐〕
We shall go, whatever may happen.〔决心〕
I shan’t speak with her.〔决心〕
You shall clean the classroom this
afternoon.(义务)
He shall give you your own money.(威胁)
※2. shall表示愿意，用在疑问句中，用于二人称表示征询听话人是否愿意，但多用will。
Shall you go with me?
3.征求听话人意见和指示，用在一、三人称的疑问句中。
Shall I turn on the light？
Shall he come to see you? ＝Do you want him
to see you?
〔六〕should
should是shall的过去式，但它同时又是一个有单独意义的情态动词。
1.表达职责、义务，作“应当〞讲，常与ought to互换。但ought to侧重反映客观情况，should侧重表示主观看法。
2.表示预测可能性，并译作“可能，〔按道理〕应该〞。
They should come here now.
3.用于委婉、谦逊地提出意见或建议。
I should think you are right.我以为你是对的。
4. should用于某些从句中表虚拟语气：
①用于表示建议、命令的动词的宾语从句中。表示建议、命令的动词有suggest〔表“建议〞时〕,
advise〔忠告〕, recommend〔推荐〕, order〔命令〕, demand(要求〕urge〔力劝〕,require(要求〕, request(请求〕,desire〔渴望〕, ask /
