情态动词

情态动词

【导学线索】

1】推测和可能性

2】必要性

3】请求，允诺，允许。

【导学目标】

4】理解情态动词的基本用法所表现出的情感态度

5】记忆辨析情态动词的特殊用法。

【基础知识】

一，情态动词的作用

表能力：can, could, be able to

表推测：must, can, could, may, might

对现在和将来的推测：情态动词+do

对过去情况的推测：情态动词+have done

表义务和责任：must, have to, should, ought to, had better.

表请求和许可：can, could, may, might, will

表意愿：will, shall, would rather.

表必要：need.

表其他：dare, used to.

情态动词表说话人对某一动作或状态的态度。如可能，义务，必要，推测等。但本身词义不完全，不能单独作谓语，必须和动词原型连用。情态动词没有人称和数的变化。每一个情态动词都有自己的具体含义，都有自己的特点。

二，can(could)

(1)表示能力。

I can speak English.

Could the girl read before she went to school?

注意：can和be able to的区别

1，can只有过去时，而be able to有多种时态变化。

2，be able to还能和除can以外的其它情态动词连用。

They must be able to come before seven.

3,过去时中，二者区别较大。Could表示过去具备某种能力，但并未作某事。

He said he could swim across the river.

Was/were able to表示过去不具备某种能力，但却成功的做成了某事，意思等于managed to do sth.

When their boat sank, Crusoeo was able to swim to the bank.

(2)表示允许。

Can /could I have a look at your new pen?

He asked whether he could take the book out of the reading-room.

(3)表示推测，可能。

1，用于肯定句中表示一段时间，理论上的可能性。

The temperature can fall to -60℃.

气温可降至零下六十度，也就是零下六十度。

Even experienced teachers can make mistakes.

2,主要用于否定句，疑问句或感叹句中。表惊异，怀疑，不相信等态度。（但还是译为可能）When can (could) they have gone to?

他们回去哪儿呢？

He can’t (couldn’t) be over sixty.他不可能超过六十岁。

How can you be so careless? 你怎么这么粗心？

三，may(might)

(1)表允许，might可以指过去时间，也可指现在时间，语气更委婉。

You may take whatever you like.

He told me that I might smoke in the room.

May (might) I ask for a photo of your baby.

在回答以may提问的问句时，多避免用这个词，而用其他方式。如：yes, please./ certainly./ please don’t./ you’d better mot./ no, you mustn’t.等，一面显得太严峻，不客气。

（2）表可能（事实上）。用于肯定句和否定句，语气不肯定。

She may not know about it.(可能不)

They might be having a meeting, but I’m not sure.

四，must

(1)表示义务。意为“必须”（主观意志），否定句中表示“禁止”。

We must do everything step by step.

You mustn’t talk to her like that.

——must we hand in our exercise-books now?

——no, you needn’t./ no, you don’t have to.

(2)表示推测。意为“想必，准是，一定”等，只用于肯定句，（must not不用于推测）。He must be ill. He looks so pale.

He looks very happy. He must have passed the exam.

(3)表示“偏要，坚持要”。常常表示与说话人愿望相反及不耐烦。

——may I smoke here?

——if you must, choose a seat in the smoking section.

Why must it rain on Sunday?

五，shall

(1)表示征求意见，用于第一，第三人称疑问句。

Shall I get you some tea?

Shall the boy wait outside?

(2)表说话人的意愿，有“命令，允诺，警告，决心”等意思。用于第二，第三人称陈述句。You shall do as I say.(命令)

You shall have my answer tomorrow.(允许)

He shall be sorry for it one day, I tell you.(警告)

Nothing shall stop us from carrying out the plan.(决心)

It has been announced that candidates shall remain in their seats until all the papers have been collected.

六，should

(1)表义务，意为“应该”（某件事宜于做），也可以用ought to, 用于各种人称，

You should be polite to your teachers.

You shouldn’t waste any time.

(2)表推测，意为“想必一定，照说应该，估计”等。

The film should be very good as it is starring first-class actors.