605情态动词讲解
一can 1.表"能力"I can lift the stone. I can speak English while he can't. Who can play the violin? He got up early yesterday so that he could catch the early bus.
could 表过去的能力。
注；1。can 与be able to表能力时的区别：
① 形式上；can有两种形式can 与could，而be able to有更多的形式。
is(are)able to, was able to ,, has been able , will be able to , would be able to 等。
be able to 只表能力而can 还可表"可能性"，"惊异","许可"等。
② could与was able to表过去能力的差别：均表过去的能力，但was（were）able to还可表业已成功的行为（即：动作确实做了）。
2．表"许可"You can go now. You can use my dictionary. You can have a rest.
-Can I smoke here?
-No, you can't.
注：用could代替can在疑问句中，语气客气委婉，但在时间上还指现在.Could you lend me your bike? Could you tell me how to get to the station?
注意：回答由could引起的问句，仍用can 而不用could。
-Could you wait a few more minutes?
-Yes, I can.
3.表猜测"可能"，一般用于疑问句和否定句。
-Can the news be true? -It can't be true. Where can he be?
注：(1)can't表"不可能"，语气断然否定。
(2) could在宾语从句中表过去的可能性，其它情况一般还表示现在的可能性只是语气比can委婉和更加不肯定。 I thought he could come .
(3) can 亦可用于肯定句表可能，但表示的是逻辑推理上的可能性（或理论上的），非主观臆断。There can be no noise on the moon because of sound being carried by the air .
(4) can(could)…have done或can(could)…have been(done)用于疑问句或疑问句表对过去时或完成时的揣测。
What can have happened to him ? He can not have read the book. He can't have been to Beijing.
4.表"惊异""惊讶"：How can you be so impolite? How can you say that?
二. may 表"允许""许可""允诺"（征询对方许可）。
You may go now . May I use your bike? You may keep the book for 2 weeks .
注意：(1)其否定形式may not表示不可以，但更常用must not来代替may not表示"不可以"，"禁止"。 -May I watch TV after supper?
-Yes, you may.(No, you mustn't .或No, you may not.或No, you'd better not.)
(2)与can的比较：may比can更正式。May I know your name? May I (he, we…)….?
×May you….? (May you have a good journey! 此处表祝愿)
（3）。might代替may用于疑问句，更客气礼貌些，回答时仍用may。
-Might I use your telephone? -Yes, you may .
(4)might not 不表示"不允许"
2．表"可能"。（1）用于肯定句和否定句（因为May I…?表征询许可）。
The news may be true . He may not be at home now. I think he may come today(tomorrow).
However fast you may run, you can't catch the fast train.
(2)用might语气更加不肯定，但指现在或将来，只有在宾语从句中might do（be）才表示过去可能性。 He might come today(tomorrow). She might have some fever .
I thought you might like something to read, so I brought some books for you .
She said she might not be at home.. I might be busy tomorrow.
(3)may not 与cannot的区别： may not"可能不"，cannot "不可能"。
比较The news may not be true.
The news can't be true .
(4) may(might)(not)+have done(been)表对过去或完成时的揣测。
Something may have happened to him . He may have been to Beijing .
3.表祝愿May you be happy! May you have a pleasant journey!
综合性补充；（1）could have done和might have done 还可以用于虚拟语气而can(may)have done 只用于揣测。
（2）表揣测用于反意问句的情况。
三must （无词形变化）
（1）。表"必须"，"应该"，"务必" must not(mustn't)表"禁止"，"不许"，"不准"，"不可以"。 Everyone must attend the lecture. The work must be finished as soon as possible.
You mustn't lend it to others.
注；对must问句的回答。 -Must I go there now?
-Yes, you must.
-No ,you ①needn't. ②need not ③don't have(got) to ④don't need to.
2.must表推测"一定"，"必定"，一般只用于肯定句，亦即用于疑问句和否定不表揣测。
（1）对现在He must be at home now. You must be hungry after the long walk.
The Chinese language must have the largest number of speakers.
(2)对进行时。 He must be sleeping now(at that time).
（3）对过去时或完成时。
It must have rained last night. He must have fallen asleep(then).
He must have gone to Beijing yesterday. She must have been young when she got married .
注意其反意问句。
3 .must表不可避免的倾向。 All men must die.
4 . must 表"偏偏"，"不巧" My car must break down.我的车偏偏坏了。
四.have to "不得不"
1. 与must的区别 （1）must表说话人的主观看法，而have to表客观需要。
比较：I have to stop smoking .(外界压力，客观情况使然)
I must stop smoking.（主观认为）
2.must只有一种形式而have to有更多的形式have to, has to ,had to ,will have to 等等。
I thought I must go there.
3.have to 的疑问，否定均须借助于do。 Does he have to go there now ?
不说Has he to go there now?
He has to go there now ,doesn't he? The work has to be finished before 10 o'clock..
4.must与had to的差别： had to还可以表示业已完成或实现的动作（即；动作确实做了）。
I had to stay at home last night.
五.ought to与should
1.两者的差别ought to语气重，偏重"责任，义务，道德、法律"等方面，"总应该"。
You ought to follow your father's advice.
注意其疑问及否定形式 -Ought he to go ？-Yes, he ought (to).
2. ought to (should)have done 表本应该做而实际未做。
You ought to have told him about the news . He shouldn't have been told about the news.
本不应该把此事告诉他（而实际告诉了）。
You should have got up early .
should have done 还可表虚拟语气
用于第一人称
3. ought to还可表示非常有可能的事。
It ought to be a close game , most probably. It ought to be a fine day tomorrow.(极可能是好天)
六.need （1） 作为情态动词①常用于疑问句和否定句②无人称和时态的变化③疑问否定借助于need本身④后跟动词原型。
（2）need作为实义动词① 有人称和时态的变化（needs，needed）②疑问否定借助于do③可有自己的宾语（可以是名词，代词，不定时）④不受什么句型限制。
I need a pen . I need to go there. He didn't need to go there. Do I need to go there? Need I go there now ? You needn't go there now. ×I need go there now.
3.needn't have done表"本不必做而实际做了"。 You needn't have hurried.你（当时）本不该匆忙。
4．对need引起的一般问句的回答： -Need I go now ? -Yes ,you must .-No, you needn't.
七.dare 1，（1）作为情态动词 ①无人称和时态变化②常用于疑问句和否定句③跟不带to的不定式。注：有固定说法I dare say…… How dare you say……?
2.实义动词①有人称和时态的变化②疑问和否定借助于do③跟带to的不定式。
比较 情态动词 实义动词
肯定句 × He dared to do it .
否定句 He daren't to do itHe dare not do it. He didn't dare to do it .He doesn't dare to do it.
疑问句 Dare he do it?Dare he not do it? Does he dare to do it?Doesn't he dare to do it?
注：（1）有时可把dare的情态和实义动词的用法揉合在一起。如；No one dared say that.
(2)在否定句中实义动词dare后的不定式"to"符号可以省略。I don't dare(to)ask her.
2.daren't have done 表"本不敢做而实际做了"。
八.shall （此处讲述的是shall情态动词而非助动词表时态）。
1． shall用于二，三人称表"命令，警告。威胁，强制。允诺"等。
用于一，三人称用来征询对方意见或请求指示。
You shall do it as I say. Tell him that he shall have the book tomorrow.
表"允诺"相当于may或can
Shall he come at once?(征询对方意见) where shall we meet ? Shall we take a walk together?
2.should (1)表"劝告，建议"Children should be taught to tell the truth.
I suggested he (should )go there. Was it necessary that my uncle (should) be informed?
(2)表"惊异"It's strange that he should have done such a thing.
（3）． 表"可能性"They should be there by now, I think.(98年高考已考过)。
九. Will 1。表"意志，意愿，乐意"，用于各人称 。（与will作助动词表时态区分开来）。
I will tell you all about it.相当于I am glad to tell you all about it.
He won't go there.他不愿意去那里。
2． Will在疑问句用于第二人称，表示询问对方的意愿或向对方提出请求。
Will you go with me for a walk? Do come to my birthday party , will you?
Will you please tell me how I can get to the station ? Won't you sit down?
3. 表示习惯性动作，有；"总是，总要，"，"惯于"的意思 。
Fish will die out of water。鱼离开水总是要死的。
He will talk for hours if you give him the chance .你要给他机会的话他总是要谈上几个钟头 。
十.Would (是will的变形，与will的用法相对应。应把would作助动词表时态区分开)。
1． 表"意愿"用于人称。 He said he would help us.他说他乐意帮助我们。
2． 表说话人的意愿或向对方提出请求，语气比will更客气婉转，但指的是现在时间。
Would you like some bananas ? I'd rather stay at home than go out .
Would you mind opening the window for me ?
注意：用would提出的一般疑问句，回答时要还原为will。-Would you help me with my lessons? -Yes, I will.
3. 表过去的习惯动作。
She would drop in on her teacher when she went to town .她总是要顺便看一下老师。
Every day she would get up early at six o'clock.过去她总是每天6点起床。
She would sit like that for hours watching ships.她过去总是坐在那里几个钟头看船。
3． 用于虚拟语气或用于科幻作品中。Such would be our home in the future.
我们未来的家庭就是这样。
十一. used to表示"过去常常"（而现在并非这样）。
We used to be good friends. There used to be a temple here. He used to go to work by bus。
He used to like fish.他过去爱吃鱼。
改为否定句：He didn't use to like fish .(He usedn't to like fish.或He used not to like fish).
改为疑问句：Used he to like fish？ 或Did he use to like fish?回答Yes, he used to .
否定式问句Use(d)n't he to like fish?
反意问句There used to be a temple here, usedn't there? （或didn't there？）
1．注：would与used to表"过去常常"的差别：
①used to表现在已不复存在的过去习惯或状态有今惜对比的含义，而would则不涉及现在。
He used to like fish.(现在不了)。He would like fish.（现在是不是这样，不知道）。
②used to 表不确定的过去时间，常常不带表确指过去的时间状语，而would常带。
③ would 表过去屡次发生的动作，所以不表状态。而used to可表状态也指动作。
？There would be a temple here.
④ would 有自觉自愿的含义，通常译作"总是，总要"，而used to只说明过去的事实，无自觉自愿的含义，常译作"过去常常"。Her would sit there, watching ships.（个人愿意）。
2．①used to do sth.过去常常做。。。②be (get)used to（doing）sth.习惯于。。。③be used to do sth.被用来做。。 与练习结合，体会掌握情态动词的用法。
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