情态动词的用法A. can; could; be able toCan 1. 表示“能力”(此时过去时是could)2.表示许可、请求，“可以”。
--Can/Could I go now?3 表示推测, 把握很大,could也可表推测,把握比can小。
--Look! Someone is coming! Who can it be?--It can’t be him. He has gone to Paris.（不可能）/ He could be here soon. 他很快就来。
4 表示感情（惊异/不耐烦）“究竟，到底”（主要用于否定句，疑问句和感叹句中。
）How can you be so foolish?What can it possibly be? 到底那是怎么一回事?They can’t be working at this time of day.5 肯定句中客观存在的可能性。
“有时会，偶尔”It can be quite windy there, especially in spring.Could 1.表示能力，can 的过去式，过去能够Could you speak English then? 那时候你会说英语吗?2. 请求允许（委婉语气）（问句的答语不用could，而用can，）Could [Can] I use your pen? ” “Yes, of course you can.”/ No, I’m afraid not.3. 表示推测可能性（肯，否，疑）We could go there this summer. 今年夏天我们可能要去那儿。
(将来可能性)You could be right, but I don’t think you are. 你可能是对的，但我并不认为你是对的。
4. could have done ①对过去推测，可能已经。
②本来能够却没做，差点就He can’t [couldn’t] have seen her there. 他不可能在那儿见到她。
He could have gone home. 他可能已回家了He could have told her, but he didn’t choose to. 他本来可以告诉她的，但他却没有。
B. may 和might1.表示允许﹑许可，might提问更委婉。
---May/Might I watch TV after supper?---Yes, you may./ Yes, please./ Certainly.---No, you mustn't. / No, you may not. / No, you can’t./No, you’d better not.2. 表示推测，有“或许”、“可能”的意思。
might把握更小。
疑问句用can/ could.•He may/might be right./ I hear there may be a few copies left.•He may/might come today (tomorrow).3. may表示祝愿，倒装。
May +主语+动词原形。
May you succeed!/May you all be happy. ☆may [might] as well…意为“不妨”、“还是…为好”等，用might 比用may 语气更委婉。
如：I’m ready，so I might as well go now．我已准备好，因此不妨现在就走。
There’s nothi ng to do, so I may [might] as well go to bed.☆may well... 完全可能C. must, have toMust 1. 表示“必须”。
否定式mustn’t表示“不可以”、“不准”、“禁止”等。
Everybody must obey the rules../You mustn’t lend it to others./You mustn’t speak like that to your mother.☆在回答有“must” 的询问时，--- Must I go now? --- Yes, you must.---No, you needn’t. / No, you don’t have to.2. must表示推测（“一定”、“必定”），表肯定的推测, 其否定的推测用can’t，表示“不可能”。
You must be hungry after the long walk. / It can't be Jim, for he has gone to Beijing.The Chinese language must have the large number of speakers.3．must 表示说话人不耐烦的态度，“干嘛偏要”☆must + have + done，表示对过去事物的肯定推测。
“一定做过...”He must have told my parents about it. 他一定把这件事情告诉我父母亲了。
☆must表示推测时，其反意疑问句应根据动词的实际时态而变化。
如：▪It must be nice to take a walk here, isn’t it?▪Tom buys a lot of apples ,he must like eating them, doesn't he？Must have done 的反意疑问句有三种情况:①从句中含有过去的时间状语,反意疑问句用过去时.▪The ground is wet , it must have rained last night, didn’t it?②从句中含有过去完成时的时间状语,反意疑问句用过去完成时.▪By the end of last term, we must have learnt 2000 words, hadn’t we?③若从句中不含任何时间状语,反意疑问句用现在完成时▪We must have been met somewhere (before), haven’t we?☆must 表示“必须”“有必要”时，反义疑问句部分用mustn’t...? 或needn’t ...?You must go home right now, needn’t you?☆must 用否定形式mustn’t时，附加疑问句部分用may或must…?You mustn’t cheat in the examination, must you?3. 表示与说话人愿望相反及不耐烦．意为“偏要”．-____you make so much noise?-Sorry, I will take care not to. A Must B Can C May D Would4. must 和have to 的区别:D. ought to/ should/ shallOught to ought to用于反映客观情况或涉及义务和规定时，常译作“应该”、“应当”(和should差不多，只是语气较强)，有时表示非常可能的事情。
•There ought not to be much noise in a hospital.•--- Ought he to go? --- Yes, he ought to.•If she is completely well, she ought to be back at school today.ought to have done指过去动作,表示一件事情该做而未做。
ought not to have done 表示一件不该做的事情却做了。
should 1.用于表示劝告和建议，“应该”．表示自己的主观看法,语气比ought to弱。
☆should + have done 指过去动作,表示一件事情该做而未做。
should not + have done 表示一件不该做的事情却做了。
--- Who did it sound like? Anybody you know?--- Well, perhaps Jeff. I should have asked who was calling before he hung it up.2.表推测，“按道理，按常理应该”They should have arrived by two o’ clock.3.表示惊讶,赞叹，不满，责备“竟然”I am sorry that you should do such a thing.4. 用于if引导的虚拟条件句中，表示一件事听起来可能性小，但也不是完全不可能。
有“万一”的意思Should I be free tomorrow, I’ll come.Ask Tom to ring me up if you should see him.shall1. shall 作为情态动词，用于第二、第三人称，陈述句，表示说话人的意愿，有“命令”、“警告”、“威胁”、“强制”、“允诺”等意思。
“必须，应，可以”．•You shall do as I say. （命令）•Tell him that he shall have the book tomorrow. （允诺）•You shall be punished if you break the law. (表警告)2. 用于第一、第三人称, 在疑问句中，shall 用来征询对方意见。
“……好吗？”“要不要……？”Where shall I wait for you?/ Shall he come at once?/ Shall we start the meeting now? 3.在条约﹑规定﹑法令等文件中表示义务或规定，用于第三人称The new regulation shall take effect on June 1st.E. will 和would1) 表示“意志”、”决心”、“意愿”，可用于多种人称。
will 指现在，would 指过去。
•I will tell you all about it./ He won’t go.(2) 表示询问对方的意愿或向对方提出请求,在疑问句中用语第二人称时，委婉语气would.•I’m going to go shopping after school. Will you go with me?•Will/would you please give him a message when you see him?(3) 表示习惯动作，有“总是”、“惯于”的意思。