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Modal Verbs
情态动词
情态动词表示说话的语气或情态。情态动词本身有词义，但不完全， 不能单独作谓语， 必须和动词一起构成谓语。
情态动词没有人称和数的变化。
大多数情态动词有过去式。
主要情态动词：
can, may, will ,must ,shall ,need, dare, had, better, would, sooner, would, as soon, could, might, would, have to, should, ought to, used to, would rather, might, as well
情态动词问题解析:
1. may be & maybe
May be (可能是)—maybe (或许)(副词)
The news may be true.
Maybe the news is true.
She may be waiting for you at home.
Maybe she is waiting for you at home.
2. May not & can not
may not 译为“可能不”、“也许不会”而非“不可以”。“不可以”为must not或can't(不许，不可以)。
---May I smoke here?
---No, you mustn't. /you can't /you can not.
The news may not be true.
You mustn't move any of the papers on the desk.
3. Can & be able to
Be able to 可以表示更多的时态。
We will be able to finish the work tomorrow.
He was not able to realize his greatest ambition.
Are you able to design a new computer program?
She has not been able to work out the complex problem.
4. ought to的否定式
ought to的否定式是ought not to，疑问句只把ought提前。
You ought to be responsible for yourself.
We ought not to look down on disabled people.
Ought we to count on him for the settlement of the debate?
5. Must
Must do
Must be
Must have done
6. Must 的反意疑问句
I must get up at six, ___?
She must be in the classroom now, _____?
They must have had great trouble trying to get there, ____?
7. 用must 提问时的回答
肯定回答：must
否定回答：needn't或don't /doesn't have to
Must I come as early as 6 tomorrow morning?
Yes, you must.
No, you needn't. / No, you don't have to.
8. Mustn't & Needn't
Must he arrive very early?
No, he doesn't have to / No, he needn't.
9. Must & have to
Must: 主观上认为“必须” 作某事。
Have to: 受客观情况迫使而“不得不” 作某事
You must work harder now if you want to find a satisfactory job after graduation.
Children in remote areas have to quit school simply because their parents cannot afford their education.
I must help him. {obligation, responsibility}
I have to help him. {unwillingness)
10. Must & have to的否定
否定must 表示“禁止，不允许，一定不要”
否定don't have to 表示“不必,不一定非得,不一定要”
We mustn't put off the trip no matter what happens.
We don't have to put off the trip, although it rains.
11. Must & have to时态的区别
Must只用于现在, 而have to则可用于不同时态。用had to表示过去 , 用will have to表示将来。
We had to resort to force in that case.
We will have to reconsider the whole thing if this plan fails.
One must have faith in life.
12. have to
have to的疑问句和否定句都要用助动词do/does，过去式则用did。
Do we have to wait for him to start dinner?
Does he have to show you the tickets to enter the cinema?
Did I have to do the other task as well?
You don't have to come in person.
She doesn't have to bring her dictionary.
We didn't have to make preparations for the quiz.
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