请问情态动词should shall will would can could must need may have t

Ⅰ.情态动词的基本用法
1.Can /could
1)表能力,有“能”“会”“能够”的意思
Can you drive a car ? -----yes ,I can No, I can’t
2) 表征求许可,意为“可以…….?”
Can I use your bike ? 我可以……? (=may, 但没有may正式)
3)表可能性,常用于否定句,疑问句
Can it be true ?
Today is Sunday. He can’t be at school. (过去式could比can更加委婉)2.May /might
1)表许可或征求对方的许可,有“可以”的意思
You may go now
May I use your computer ?
注：过去式might 表示的语气更加委婉,客气
Might I use your pen for a while ?
回答以may 开头的疑问句有如下表达法：
May I smoke here ?
---------Yes , you may. No, you can’t.
---------Yes, please. No, you mustn’t
No, you’d better not.
2)表猜测,通常只用于陈述句.
You may be right.
在口语中can 可以代替may 表示许可,但can较随便,may 更正式
Can I use your bike ,John?
May I have a look at your license please,sir ?1.Must
表义务,“必须”
You must talk to them about their study.
在否定结构中,表不许,禁止
You mustn’t smoke here.
注意must 的回答
Must I clean the dining room at once ?
-----Yes, you must .
------No, you needn’t .
------No, you don’t have to .
3)表坚定的建议
You must come and see us as soon as you get to shanghai.
3)表推测,暗含有很大的可能性
He must be ill .He looks so pale .4.Have to
表“不得不”,强调“外界压力,不得已而为之”
Have to 的否定式表‘不需要’ mustn’t表‘不允许’
You don’t have to go there .
You mustn’t go there .5. Need /Dare
1）need 表示“需要,必须”,作情态动词时,仅用在否定句和疑问句中,在肯定句中一般用must , have to , ought to , should 代替
You needn’t worry
Need you go ?
No , I needn’t .
Yes I must.
2）dare作情态动词时,主要用于疑问句,否定句和条件从句中,一般不用在肯定句中.
How dare you say I’m unfair ?
He daren’t speak English before such a crowd , dare he ?
3) dare和need 常用作实义动词,有时态,人称和数的变化.所不同的是,作实义动词时,在肯定句中,dare后面通常接带to 的不定式,在否定句和疑问中,dare后面可接带to 或不带to的不定式.
I dare to swim across this river .
He does not dare (to) answer .
Don’t you dare (to) touch it !
He needs to finish it this evening . 6. Will / Would
Will 1）表意愿
I will help you .
2)用于第二人称征求意见
Will you have some more wine ?
3)用于第三人称表推测
-------Somebody is coming upstairs
-------That will be Mary.
4)表将来或现在的习惯
He will come this afternoon
The old man will sit by the window for hours.
Would 1) 表过去的意愿
I’d like to see Mr. Smith
2)表过去的习惯
When I was a child , we would get up early and go climbing .
3)表征求意见,语气比will 委婉
Would you mind my smoking here ?7. Shall /Should
Shall 1)用于第一,第三人称,表征求意见或建议
Shall we go out for lunch ?
2) 用于第二,第三人称陈述句,表示一种强烈的感情：如命令,警告,禁止,威胁,允诺等语气
If you dare do that , you shall be punished .
3) 表示规章,指示,预言等
All shall die
Should 1）表示劝告,义务,建议,命令,其同义词是ought to ; 在疑问句中,通常用should代替ought to .
We should learn some English .
You should go to class right away .
Should I open the window ?
Should 的含义较多,用法较活,现介绍三种特殊用法
I should think it would be better to try it again . （我倒是认为最好再试一试）
You are mistaken , I should say . (依我看你是搞错了)
I should advise you not to do that . （我倒是劝你别这样做）
从以上例句可以看出：情态动词should用于第一人称时可以表示说话人的一种谦逊,客气,委婉的语气
Should还可以用在if引导的条件从句,表示一件事听起来可能性很小,但也不是完全没有可能,相当于“万一”的意思. 从句谓语由should加动词原形构成,主句谓语却不一定用虚拟语气
Ask her to ring me up if you should see her (你万一见到她,请让她给我打个电话)
If you should change your mind , please let us know . （ 万一你改变主意,请通知我们）
`should I (if I should ) be free tomorrow I will come . （万一我明天有时间,我就来.）
此外,Why (or How)+ should 结构表示说话人对某事不能理解,感到意外,赞叹,愤怒、惊异等感情,意为“竟会”
Why should you be so late today ? （你今天怎么来得这么晚?）
--------Where is Betty living ? （贝蒂住在哪里?）
------How I should know ? （我怎么会知道呢?）
I don’t know why you should think that I did it .
(我真的不知道你凭什么认为这件事是我干的)
2)should 表示允诺
It should be ready at noon .
表示推测或可能
They should finish it by now .Ⅱ 情态动词表“推测”的用法
1)情态动词+动词原形 --------表示对现在事情的推测
2)情态动词+ have done ------表示对过去状况的推测和判定
具体用法如下：
must have done 用在肯定句中,表示对过去状况的肯定性推测,意为“过去一定已经做了某事”.
can have done 用在否定和疑问句中,表示对过去状况的否定或疑问性推测,意为“过去不可能做某事；过去做了某事吗?”
could have done 表示“过去可能已经做了某事”或者表示“过去本来可以做某事,却没有做”.
may/might have done 用在肯定句或否定句中,表示不确定的推测,意为“过去可能,也许做了某事”.
needn’t have done 表示“过去做了本来不必做的事情”
should /ought to have done 用在肯定句中,表示“过去本该做某事,却没有做,”用在否定句中,表示“过去不该做某事,却做了”.
E g 1 . I -----have been more than six years old when the accident happened .
A. shouldn’t B couldn’t C mustn’t D needn’t
2. He -----have completed his work , otherwise, he wouldn’t be enjoying himself by the seaside. A .should B must C wouldn’t D can’t
3 .This cake is very sweet . You -------a lot of sugar in it .
A. should put B could have put C might put D must have put
4. ------Tom is never late for work . Why is he absent today ?
--------Something ---------to him .
A. must happen B should have happened C could have happened D must have happened
5. I was on the highway when this car went past followed by a police car. They -----at least 150 kilometers an hour .
A. should have been doing B must have been doing
C. could have done D. would have done
( answer: 1---5 BBDDB )

Ⅲ. 情态动词在虚拟语气中的用法
虚拟语气表示说话人的愿望,假设,猜测或建议,而不表示客观存在的事实, 虚拟语气通
过谓语动词的特殊形式来表示.
表示与现在事实相反的假设时,条件状语从句中的谓语动词用“过去式（be的过去式用were）”,而主句中的谓语动词用“would (should ,could , might ) +动词原形”.
If I were you , I should study English .
If he had time , he would attend the meeting .
表示与过去的事实相反的假设时,条件状语从句中的谓语动词用“had +过去分词”,而主句中的谓语动词用“would (should ,could , might ) + have +过去分词”
If you had taken my advice , you wouldn’t have failed in the examination .
不定式的完成时可表达与过去事实相反的假设.
To have studied harder, you would have passed the exam .
表示与将来事实相反的假设时,条件状语从句和主句所用的谓语动词与“表示与现在事实相反的假设”的谓语动词相同,或者条件从句中用“were to (should)+动词原形”.
If you came tomorrow, we would have the meeting .
If it were to rain tomorrow , the meeting would be out off .
当条件状语从句表示的行为和主句表示的行为所发生的时间不一致时,动词的形式要根据它所表示的时间来调整.
If you had worked hard , you would be very tired . (从句说的是过去,主句指的是现在)
6）以上句型可以转换成下列形式
-----省略if , 用Were, had ,should+主语
Were I in school again , I would work harder .
Had you been here earlier , you would have seen him .
Should there be a meeting tomorrow , I would come .
但 在虚拟条件状语从句中,省略连词的倒装形式的句首不能用动词的缩略形式
Were it not for the expense , I would go to Italy .（不能用weren’t it for.

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