高考英语语法：情态动词

情态动词有一定的词义, 表示某种感情或语气, 是不完全动词, 不能单独作谓语, 需和实义动词一起构成谓语. 常见的情态动词有: can / could, may / might, must, shall / should, will / would, need, ought to, dare / dared等

一.may / might的用法:

1.表示可以, 即表示说话人许可或请求许可

a. You may take it away.

b. May I come in ?

2.表示可能, 也许 (在疑问句中通常不用may / might, 而用likely, do you think, can等表示是否可能, 会不会的意思)

a. He may come today.

b. Is it likely to rain ?

c. Do you think the train will be late ?

d. Can the news be true ?这消息会是真的吗?

3.在提建议时, 可用May I ?

a. May I carry your bag ?

b. May I make a suggestion ?

二.can / could的用法:

1.表示许可或请求许可, 相当于may. 但can比may用得更广泛. can不仅表示说话人同意, 准许, 还可以表示客观条件许可. may通常只表示说话人同意或准许

a. The class is over. You can go home now.

b. You can go there tomorrow.

c. Can I borrow your car for today ?

2.在提建议时, 可用Can I / you ?

a. Can I buy you a drink ?

3.表示会, 能, 相当于be able to

a. He can speak English.

b. Can you play tennis ?

c. Little Tom can’t move the big box.

4.在疑问句中表示怀疑, 不确定或不会有的情况, 即否定的推测

a. Can it be true ? 这是真的吗?

b. Can it be true that he has passed the exam ? 他真的通过考试了吗?

5.can’t / couldn’t在陈述句中可表示肯定不, 一定不的意思

a. He can’t be in the room right now.

b. It can’t have rained last night, for the ground is dry.

6.can’t / couldn’t help doing sth表示不得不,忍不住做某事

a. People couldn’t help laughing at the foolish emperor.

7.can / be able to do的区别:

①.be able to可用于各种时态, 而can只有现在时can和过去时could

②.be able to可以和另一个不完全动词连用, 如should be able to (应该能够), must be able to (必须能够)等, 而can则不可以这样用

③.强调能力时, 多用be able to

a. The patient was soon able to sit up and read.

④.can可用于人或其他事物作主语的句子中; be able to只用于有生命的名词或代词作主语的句子中

三.must的用法:

1.表示必须, 它的否定形式是need not / needn’t, 而不是must not / mustn’t, mustn’t表示禁止或不许做某事

a. You must set off at once.

b. You needn’t tell John about it.

c. You mustn’t play with fire.

2.表示肯定是, 一定是的推测意义; 与此对应, 表示肯定不,一定不用can’t, 而不用mustn’t

a. You must be very tired now.

b. If he had really been there, I must have seen him.

c. He must have gone away. We don’t see him anywhere.

3.must / have to的区别:

①.must / have to一般可以通用, 但must侧重于说话人主观上的看法, 即说话人认为必须; have to侧重于客观上的需要, 含有客观上不得不之意

a. If the person is not breathing, you must try to start his breathing.

b. You must / have to study with a teacher if you want to know how to do first aid.

②.must没有时态的变化, 一般用于表示现在或将来; have to有时态的变化, 可用于过去, 现在, 将来各种时态

a. We must study hard when we are young.

b. I think she must remain in hospital for a week.

c. We had to stay there for a whole day because of the rain.

d. We have to practise a lot if we want to speak English well.

e. The situation has changed; we will have to change our plan.