情态动词的用法总结

情态动词的用法总结2

情态动词表示可能、必要、允许、愿望、猜测等意义，它们本身虽有一定词义，但不能独立用作谓语、也没有人称和数的区别，其后必有动词原形，共同构成复合谓语。

possibility: can / could, may / might certainty: must, will, should

ability: can / could, be able to permission: can / could, may / might

requests: can / could, will / would suggestions: could / may /might, shall

necessity: must, have to, have got to, need advice: ought to, had better

语法特征

1. 情态动词没有人称和数的变化,即情态动词第三人称单数不加- s (have to, have got to, be able to 除外)。

2. 情态动词不能表示正在发生或已经发生的事情,只表示期待或估计某事的发生。

3. 情态动词本身具有一定词义,但不能单独做谓语, 后一般接动词原形一起构成谓语部分(ought to, have to/have got to, be able to除外)。

4. 情态动词无非谓语形式,即无不定式、分词等形式。

1. can和be able to

1) can (could) 表示能力、可能, 只用于现在式和过去式can表能力时意味着凭体力或脑力或技术等可以做。I can climb this pole. He is only four , but he can read. Fire can't destroy gold.

因为can不能和其他助动词连用，所以表示将来式时用will be able to ：

You will be able to skate after practising it times.

2)表可能性Can the news be true? It can't be true. What can he possibly mean?

3)表示允许（和may意思相近）常见于口语。Can (May) I come in ? 我能进来吗？Can I smoke here ?

could表过去的能力、可能和许可，（间引）At that time we thought the story could not be true.

4) be able to可以用于各种时态。只用be able to的情况：a. 位于助动词后。

b. 情态动词后。

c. 表示过去某时刻动作时。

d. 用于句首表示条件。

e. 表示成功地做了某事时,只能用was/ were able to,不能用could。

注意:could不表示时态,只表示：

1) 提出委婉的请求,回答中不可用could。--- Could I have the television on? --- Yes, you can. / No, you can't.

2) 在否定、疑问句中表示推测或怀疑。He couldn't be a bad man.

2. may和might

1) 表示允许或请求;表示没有把握的推测;may 放在句首,表示祝愿。May God bless you! He might be at home.

注: might 表示推测时,不表示时态。只是可能性比may 小。

2)当回答由may 引起的问题时，否定答语要用must not,表示"不许可"、"不应该"、"不行"。

May I come in? ( = can ) Yes, you may. No, you mustn't.

3)表建议（可和as well 连用）成语:may/ might as well,后面接不带to 的不定式意为"不妨"

e.g. If that is the case, we may as well try. You may as well stay where you are.

might 1)表过去的"可能"和"允许"多用于间接引语She said that he might take her dictionary.

除在间接引语中外，might一般不表示过去的"可能"与"许可"。表过去的"可能"可用could，表过去的"许可"可用were (was) allowed to。2)表现在的"可能"，其可能性要比may小。Electric irons could be dangerous; they might give you a severe shock.

3. have to和must

1) 两词都是"必须"的意思, have to 表示客观的需要, must 表示说话人主观上的看法, 即主观上的必要。e.g. My brother was very ill, so I had to call the doctor in the middle of the night. 1、must 的主要用法。

1)表示必须、必要We must do everything step by step .

2)must 的否定式有两个：当回答由must引起的问题时，否定答复要用needn't或don't have to 表"不必"、"无须"、"用不着"、"不一定"的意义。当表示"不应该"、"不许可"、"禁止"时，就用must not。

Must I go tomorrow? 明天我必须去吗？Yes, please.是的，请吧！No , you needn't.( = don't have to ) 不，你不必去。You must not smoke here. 你不准在这儿吸烟.

have to的含义与must是很接近的,只是have to 比较强调客观需要，must 着重说明主观看法。

I must clean the room.（主观想法）It's getting late. I have to leave now.（客观需要）

另外，have to 能用于更多时态：We had to be there at ten . We will have to reconsider the whole thing.

have to 的否定式：don't have to do "不必做……" 。You don't have to go right now.

2) have to有人称、数、时态的变化,而must只有一种形式。但must可用于间接引语中表示过去的必要或义务。e.g. He had to look after his sister yesterday.

3) 在否定结构中：don't have to 表示"不必"; mustn't表示"禁止"。You mustn't tell him about it.

4. 情态动词ought to 的用法。Ought to 后接动词原形，表义务，但不及must 那样具有信心:

You don't look well. You ought to go to the doctor.

Ought to 用于否定句，可缩略为oughtn't to。You oughtn't to smoke so much.

也可以用于疑问句，如：Ought you to smoke so much?你应该抽这样多烟吗？

Ought to 在间接引语中表过去时形式不变，如：He said you ought to tell the police.

5. 情态动词shall与should 的用法

1、shall的用法