情态动词与助动词（高中）

情态动词与助动词

一、情态动词的概念和种类

情态动词具有一定的词义，没有人称和数的变化，不能单独构成的谓语，和谓语动词连用表示委婉语气，可以表示愿望、态度或推测等。 英语的情态动词有下列几种：

can could may might must need dare will would used shall should 二、can和could

（一） 表示能力

表示天生或学到的能力，can表示现在的能力，could表示过去的能力。 Hold still so we can finish fixing ou. Who an prove it?

He could swim across the river even in his later years.

(二)表示可能性（可以，可能）

表示此义的can是表示理论上的可能性，如果表示的是实际上的可能性的话，则使用could或may.

Science has now provided answers to almost every question man can ask. Anybody can make mistakes. He may be very busy these days. It could be better to stay here.

Can you come and see me tomorrow?

(三)表示许可

can表示许可时，是may在非正式场合的替代词。 Mother said we could do anything we wished.

You can borrow two books at a time from the library.

(四)表示推测

can和could表示推测，通常用于否定句或疑问句中，通常有两种句型。

1. 表示对现在或将来情况的推测，其结构是：can/ can’t/ could/ couldn’t +动词原形或

be

She couldn’t make mistakes on this matter. What do you think this letter can mean? That can’t be the milkman. It’s too early.

2. 表示对已经发生的情况进行推测，其结构为：

can/can’t/could/couldn’t+have+过去分词 He couldn’t have said such a thing.

Where can John have put the matches? He can’t have thrown them away. (五)can (could)与be able to的区别

can表示能力时（既有某种知识和技能而能办到），可与be able to互换，但在将来时和完成时中必须用be able to；表示经过努力而成功地办到了具体的事情时，只能用be able to。这种用法的be able to相当于succeed in或manage to。另外，can not比cannot更强调。 I can (am able to) speak Russian. She couldn’t climb the mountain.

He has been able to finish the work on time.

She could( was able to) read novels when she was three years old. He was able to pass his examination as a result of his hard study.

三、may和might的用法

(一) 表示许可用may,提问时否定回答可用may not或mustn’t, mustn’t 语气更重，用you’d

better not回答更温和、有礼貌 You may use my dictionary.

My boss told me I might have a vacation.

May I borrow your toothbrush? No, you may not. (二) 表示可能性，推测

通常用于肯定句中。表推测具体有两种用法。 1. 表示对现在或未来情况进行推测，其结构为：“may (might)+动词原形或+be+现

在分词

2. 表示对已经发生的情况进行推测，其结构为：“may (might) +have +过去分词

Potter and his friends may have simply been in the wrong place at the wrong time. I think it might rain.

He may be having the meeting now.

They might have known the matter earlier.

He thought it might be wisee to try his luck there.

(三) may表示祝愿（通常用倒装结构）

Long may you live!

May success attend you! Happy may your birthday be! May you have merry Christmas! (四) 用于让步状语从句

Whatever he might say, no one believed him.

However hard you may try, you will never be able to take part in the Olympic Games. (五) 用于固定搭配中

may well+动词原形，意为“理应，有足够的理由”；意为“还不如，不妨”。 It may well rain.

He may well be proud of his son.

I might (just) as well stay at home tonight.

You might as well throw your money into the sea as lend it to him. 四、must的用法

（一） 表示责任，义务，或强调主观看法。Must开头的问句，其否定回答要用needn’t

或don’t have to

You must keep it a secret. We must obey all the rules. Mus I do it at once? Yes, you must. (No, you needn’t.或No, you don’t have to.)

（二） 表示必然的结果

All men must die. Truth must be out.

(三)表示说话人不允许或禁止某人做某事，通常用于否定句 You must not speak ill of others. They must not leave their rooms.

(四)表示推测，用于肯定句。通常有两种形式

1.表示现在或未来情况的推测，其结构为：must+动词原形或must+be+现在分

词。

Alice must have been taking Edward’s car home so that he could keep me from making a run for it.

He must be coming this moment. Poverty must follow after a long war.

There must be something wrong with the machine. The article must have been written by a woman. It must have rained last night, for the ground is wet.

(五） 表示过去的不巧，语意为“偏偏、不巧”

Just when I was busy, the neighbor must come and chatter.

（六）must与have to的区别 1.含义不同。Must表示“必须”，通常着重于说话者的主观看法，认为有义务，有必要做某事；have to着重表示客观的需要，含有“不得不”的意思。

2.形式不同。

must只有一种形式，可用于现在时，过去时（多用于间接引语中）。而have to却有四种形式，即：have to, had to, will/ shall have to, would/ should have to.

He will have to be there before ten.

She said she would have to get her tiket for the train. You must be back before 10 o’clock.

You have to be back before 10 o’clock because the train is to leave at 10:15. 五、need和dare的用法

这两个词作情态动词用时，无人称变化，只用于否定句，疑问句和条件句。

（一） need表示需要，也可用于在过去时中；dare表示敢于，其过去式为dared

He dared not go out at night. Mary dare not touh the snake. Need she go downtown yesterday? There need be no hurry, need there? If I need start early, I will.

(二) need not have+过去分词，表示“不必做某事，但却做了” need have +过去分词,可用于比较结构中。 You did not have to ask for about it.

He drove faster than he need have done. You need not have asked her about it.

(三)need的肯定式为must，否定式为needn’t You needn’t see him, but I must. You needn’t do it at once, need you?

(四)need和dare也可用作实义动词，作实义动词时，要注意人称和时态的变化 Does it need to be done so soon?

The garden needs watering ( to be watered).

A fence needs the support of the three sankes, doesn’t it? He had never dared to ask here to go anywhere with him.

(五） dare作实义动词时，在疑问句或否定句中，其后面的不定式符号常省略，但当

同dare同shall, will, should, would, have, had连用时，后面的to不省略 I will not dare to climb the tree.

Does the little girl dare (to) enter the house in the darkness?

六.will、would和used to的用法

(一)表示命令，请求或建议（这时will和would通用，而would更委婉，也可用won’t） I wish you would let me pack my own things! Won’t you sit down?

Will you please go with me?

Go and get the newspaper, will you?

Would you like to have lunch with us today?

(二)表示意愿或主张。用于非人主语时，表示固有性质，倾向。Will表示现在或经常性情况，would表示过去的情况；表示主语过去强烈的意志或主张“无论如何都想…，一定要…” The door won’t shut. I wil never do that again.

I will marry you whatever happens.

His father was angry because he wouldn’t obey him. The manger would have his won way. (三)will表示客观事实 Oil will float on water. Fish will die out of water.

(四)will在if条件状语从句中，表示意愿，请求或拒绝等 If he will pay, I’ll go with him.

If you will help u, we can finish it early.

If he won’t go with you, I shall ask somebody else.

（五）will和would表示推测，通常的含义为“想必”，“也许”，“大概”，“可能”。下面是英语中表示推测的情态动词，其程度由低到高位：might-may-could-can-should-ought to-would- will- must

It would be about ten o’clock when he left home.

There is a ring at the door. That will be the post man, I suppose.

（六） used to和would用法比较

used to和would都可表示过去时间经常的习惯动作，would表示过去经常重复的习惯动作，可以表示不规则的习惯，不表示状态，would没有与现在对比的意思，或许动作现在还在进行；used to则强调过去与现在的对比，并表示目前不复存在的习惯，可以和动作动词或状态动词连用，即可以表示持续的状态，也可以表示重复的行为。 He would read deep into the night.

He used to have a car（表示状态，不用would） He used to get up at half past five in the morning.

注意：used to的否定句和疑问句 Used you to play footaball?

Did they use to go out a lot together for meals? He used to live there, didn’t/ usen’t/ usedn’t he? He usedn’t/ don’t use/ used not to smoke, did he? 七、shall的用法

（一） 用在主语是第一人称或第三人称的疑问句中，表示征求意见或请求指示

Shall she come right now? Shall I fetch a docotr for you?