五、情态动词
情态动词有can, could, may, might, must, should, ought to, need, dare, had better, would rather 等。情态动词相当于助动词，不能单独使用，必须再接动词原型。ought to 整个相当于情态动词，否定是在情态动词后加not，但是ought to的否定是ought not to。
1.can, could
表示能力、允许、客观可能性。
She is only four, but she can read.
Is there anything that I can do for you?
This sort of thing can't go on.
I couldn't follow her speech.
Could you lend me your bike?
Fire can't destroy gold.真金不怕火练
2.may, might
表示允许、猜测。
The dialect of one province may be quite different from that of the next one.
Students may not stay out after midnight without written permission.(stay out 在外边待的很晚)
He asked his mother if he might go out to play.
"May I open the window?" "Yes, please./ Please don't./ No, you mustn't." (may 如果要否定用mustn't，could和might用在现在时表委婉的说法)
3.must
表示"肯定"、"准是"，还可以表示"必须"，与have to 意思接近，但must 侧重说明主观看法，have to 强调客观需要。must时主观表达方式，have to是客观表达方式。mustn't 表示"千万不要"、"一定不要"。
If you must go, at least you wait till the rain is over.
Teachers always tell us we must do everything step by step.
--Must I go tomorrow?
--No, you needn't.(Yes, I'm afraid so. must一般疑问句的否定用needn't来回答)
He has to tidy up the room everyday.(tidy up 打扫干净)
(He must tidy up the room everyday.)
We have to study a foreign language.
You mustn't talk like that to your parents.
4.ought to , should
表示应该做的事和非常可能的事。
You ought to go to see a doctor for you don't look well.
You shouldn't talk like that.
The old man said you ought to tell the police.
You oughtn't to smoke so much everyday.
The work ought to be finished by next Friday.
The book should be available in the bookstore. (available 可得到的)
5.need
表示"需要"。need可以当情态动词，也可以做实义动词。
Need I come?-Yes, you must.(No, you needn't)
All you need do is to say yes to his questions.
He said he needn't hurry.
need 还可以作实义动词，后面接动名词时相当于被动结构。
You don't need to stay.(=You needn't say. )
Does he need to know it?(= Need he know it?)
needs/ wants/ requires +doing相当于被动语态。
The question needs/ wants/ requires discussing.(=needs to be discussed.)
My shoes need repairing.(My shoes need to be repaired.)
物作主语时need接doing表被动。
6.dare
表示“敢”，也可以作实义动词，主要用于否定句、疑问句。
The boss is so hot-tempered that no one dare tell him the bad news.(so……that 如此……以至于)
Who dare stop you?
He doesn’t dare to look out of the window.
情态动词没有人称性数的变化，有人称性数变化的一定是实义动词。
She dare not say what she thinks.(=She doesn’t dare to say what she thinks.)
7.had better
表示“最好”。否定为 had better not
I had better not disturb him.
We had better go and see the doctor now.
8.would rather
表示“宁愿”，后面接从句时，从句的谓语用一般过去时。否定用would rather not。
I’d rather not say anything.
John would rather work in a company than in a factory.
She would rather have the small oranges than the large ones.
I would rather you came tomorrow.
(would sooner 迟早，后的宾语从句用虚拟语气，一般过去时。)
I would sooner she left the heavy end of the work to someone else.
有些情态动词，如can, could, may, might, must, ought to, should 后面可以接动词的完成形式，表示对已经发生的事的猜测或对应该发生的事的看法。
They shouldn’t have left so soon.
They must have been through a lot.
I needn’t have told them that.
He can’t have left for Shanghai for I saw him a moment ago.
How could you have forgotten such an important thing?
They must have arrived by now.
You oughtn’t to have done that.
She looks so miserable. You oughtn’t to have hurt her feelings.
“I was late yesterday because my car broke down. ”(broke的原型是break，这里表抛锚的意思) “You should have borrowed mine. I wasn’t using it. ”
情态动词部分除了应了解每个词的具体含义之外，情态动词的否定是在后面加not。特别要注意had bette和would rather的否定。ought to的否定是ought not to。would rather后面接句子只能用一般过去时。can、could、may、might、must、ought to、should后接动词完成式表示对过去事情的猜测。
“may/might + 现在完成时”表示“也许已经……了”;
“must + 现在完成时”表示“肯定……了”;
“can / could + 现在完成时”表示“本来是能够……的(实际上未)”;
“should/ought to + 现在完成时”表示“本应该……(实际上未)”。
1.That was in March. You may / might have read about it in the newspapers.
2.The house is dark; the Browns _______ to bed.
A. may go B. should go C. should have gone D. must have gone
(答案 D)
3.Her husband could have helped her, but he chose not to.(choose)
4.You _______ yesterday if you were really serious about the job.
A.ought to come B. ought come C. ought to have come D. ought have come
(答案 C serious 严肃的)
此外，考生还应注意need和dare这两个词，它除了是情态动词外，还可以是实义动词，在不同的情况下用法有差别
1.To travel from England to Scotland you _______ a passport.
A. mustn’t have B. haven’t got C. don’t need D. needn’t
(情态动词后要接动词原型 答案 C)
2.The house needs ________, but they plan to wait until next spring to do it.
A. paint B. to paint C. painting D. be painted
(答案 C)
1. “Do you have to leave?”
“Sorry , but I really _____.”
A. have B. had to C. do so D. must
答案 D
2. I want to go to the dentist, but you ________ with me.
A. needn’t to go B. needn’t go
C. don’t need go D. need go
neen't为情态动词，后接动词原型
don't need为实义动词，后面接to
答案 B
3. “______ you pass me the salt?”
“Sure. Here you are .”
A. Might B. Must C. Could D. Need
答案 C
4. “I haven’t felt well for a week.”
“You ______ see a doctor.”
A. have ought ot B. had better
C. should have to D. would rather
答案 B
5. “Doesn’t Elaine want to see that movie?”
“Yes, but she says _______ go tonight.”
A. she’ll rather not B. she’d rather not
C. she’d not rather D. she won’t rather
would rather的否定词放在rather的后面，动词的前面。
答案 B
6. “Listen, Mary is singing in the next room.”
“That ______ be Mary. She’s in hospital.”
A. may not B. shouldn’t C. should have gone D. can’t
答案 D
7. John ______ a restless person. He kept moving from country to country.
A. must be B. should go C. must have been D. must have gone
答案 C
8. I can’t find Tom anywhere. I think he ____ to the library.
A. may go B. must go C. must have gone D. should have gone
should have gone 应该……而实际上没……
答案 C
9. “What’s the matter with that picture on the wall?”
“It needs _________.”
A. straightening B. to be straightening C. straightened D. straighten
答案 A
10. “Tom graduated from college at a very young age.”
“He _________ an outstanding student.”
A. must be B. could be C. must have been D. should have been
对过去推测，情态动词后接现在完成时。
答案 C
11. The old lade needs ________ after her shock.
A. to comfort B. comforting C. to be comforted D. Both B and C
答案 D
