情态动词专题精解一、情态动词的基本用法（一）情态动词的特点1. 没有人称和数的变化。
2. 有些情态动词有过去式的变化：will → would , can → could , may→ might , dare → dared（二）can (could)1. 表示能力。
Eg: Two eyes can see more than one.2. 表示允许。
Eg: Can I have a look at your new pen?Can (Could) you lend me a hand?3. 表惊异、怀疑、不相信等态度。
主要用于否定句、疑问句或感叹句中。
Eg: Where can (could) they have gone to?He can’t (couldn’t) be over sixty.How can you be so careless?4. 表示猜测 (肯定句把握较小；否定句几乎为100%把握)eg:The temperature can fall to 10℃.You can’t be serious.(三)may (might)1．表允许，might是may的过去式; 用在疑问中比may委婉、客气。
Eg: You may take whatever you like.He told me that I might smoke in the room.2. 表可能（事实上）。
语气不肯定。
Eg:He may be at home. 他可能在家。
She may not know about it.I am afraid they might not agree with him.They might be having a meeting, but I’m not sure.(三)must1. 表必须（主观意志）eg: We must do everything we can to help him.You mustn’t talk to her like that.--Must we hand in our exercise books now?--No, you needn’t. / No, you don’t have to. /yes,you must.2. 表示很有把握的推断，意为“想必、准是、一定”等，只用于肯定句。
have (has)to：eg: have (has)got to 必须, 不得不。
过去式为had to。
He must be ill. He looks so pale.She must have a lot of money, for she drives a BMW.(四)shall1. 表征询意见，用于第一称疑问句。
Eg:Shall I get you some tea?It's a fine day. Let's go fishing, shall we?2. 表说话人的意愿，有“命令、允诺、警告、决心”等意思，用于第二、第三人称陈述句。
Eg:You shall do as I say. （命令）You shall have the English book as soon as I finish it.（允诺）He shall be sorry for it one day, I tell you. （警告）Everything that he owns shall be taken away from him.（决心）(五)will1. 表意愿，用于各种人称陈述句。
Eg: I will do anything for you.If you will read the book, I’ll lend it to you.2. 表请求，用于疑问句。
Eg: Don't smoke in the meeting room, will you?Won’t you drink some more coffee?3. 表示某种倾向或习惯性动作。
Eg: Fish will die out of water.The door won’t open.(六)would1. 表意愿。
Eg: They would not let him in because he was poorly dressed.2. 表委婉地提出请求、建议或看法。
Eg: Would you like another glass of beer?3. 表过去反复发生的动作或过去的一种倾向。
Eg: Every time she was in trouble, she would go to him for help.(七)should1. 表义务。
意为“应该”，用于各种人称。
Eg: You should listen to the doctor's advice. 你应该听从医生建议的。
You should study the article carefully. 你应该仔细读那篇文章。
2. 表推测，意为“想必一定、照说应该、估计”等。
Eg: The film should be very good as it is starring first-class actors.那部电影想必很棒，都是一流的演员。
They should be home by now. 现在他们应该已经到家了。
(八)ought to1. 意为“应该”，口气比should稍重。
Eg: Ought you to smoke so much? 你应该抽这样多烟吗？You ought to write to the mayor. 您应该给市长写信。
2. 表推测，暗含很大的可能。
Eg: She ought to know his telephone number. 她应该知道他的电话号码。
(九)used to 过去常常, 现在不复发生或存在。
Eg:The Greeks used to worship several gods. 过去,希腊人崇奉好几种神。
He used to smoke. 他过去抽烟（现在不抽了）。
二、情态动词的推测用法⒈肯定句中：must (一定)，may (可能)，might/could (也许，或许) 其语气的肯定程度依次递减。
其中，might 和could并非过去时态，只是语气较为委婉或可能性较小⑴对当前行为、情况或状态的推测：must /may /might /could + do/beeg: He must/may/might/could be in the reading room. 他肯定/可能/也许在阅览室里。
I must look funny in this hat. 我戴这顶帽子看起来一定很滑稽。
⑵对此时此刻正在进行的动作的推测：must /may/ might/ could + be doing 想必/可能正在……Eg:He must /may/ might/ could be watching TV at this time.他此时一定/可能/或许在看电视。
They must be waiting for us. 他们肯定在等着我们。
⑶对过去发生的事情的推测：must /may /might /could + have +过去分词想必/可能已经……Eg: They must have arrived by now. 现在他们肯定已到了。
You look very tired. You must have stayed up last night.看上去你很疲劳，你昨晚一定熬夜了。
You may have read about it in the papers. 你可能在报上已读到这件事了。
⑷过去的一段时间内一直在进行的动作：must/may /might/ could + have + been +doing 想必/可能一直在……Eg:They are sweating all over. They must have been working in the fields.他们浑身是汗，准是在地里劳动来着。
He may have been waiting for us for an hour. 他可能等我们一小时了。
2．否定句中：can/could not 不可能，想必不会may/might not 可能不⑴对当前行为、情况或状态的推测：can/could not+动词原形不可能，想必不会may/might not +动词原形可能不eg:He may not be busy now. 也许他现在不忙。
He can not be busy now. 他现在一定不忙。
He can’t be in the reading room. I saw him on the playground just now.他不可能在阅览室里，我刚看到他在操场上。
⑵对此时此刻正在进行的动作的推测：can/could not + be doing 不可能，想必不会在干某事may/might not + be doing 可能没在干某事eg: They can’t be telling the truth. 他们不可能在说真话。
They may not be telling the truth. 他们可能没在说真话。
⑶对过去发生的事情的推测：can/could not + have +过去分词不可能，想必不会做过某事may/might not + have +过去分词可能没干过某事eg: He can’t have finished the work so soon. 这项工作他不可能完成得这样快。
He may not have achieved all his aims. But his effort is a good one.他可能没达到他的全部目的，但他还是认真做了努力的。
⑷过去的一段时间内一直在进行的动作：can’t /couldn’t/may not have been doingeg:He can’t have been waiting for us so long. 他不可能等我们那么长时间。
3．疑问句中：常用can/could来表示说话人的猜疑、怀疑或不肯定的语气⑴对当前行为、情况或状态的推测：can/could + 主语+ do/beeg:Where can he be now? 他现在会在哪里呢？Can it be true? 那会是真的吗？⑵对此时此刻正在进行的动作的推测：can/could +主语+ be doingeg:It’s so late. Can Tom be reading? 这么晚了，汤姆还在看书吗？What can he be doing? 他可能在做什么呢？⑶对过去发生的事情的推测：can/could +主语+have doneCan she have told a lie? 她会不会说谎了？Where can she have gone? 她会上哪儿去了呢？三、“情态动词+完成式”的用法1. should(n’t) have done表示本该做的事情实际上并未做，或者本不该做的事又做了。