情态动词I can , could (could 是can的过去式)1）表示“能力”，“许可”，“可能性”，“惊异”。

He can sing. （能力）He could sing when he was young.（能力）You can go now. (许可)At that time, I didn’t think the story could be true. (可能性)What on earth can this mean? (惊异)2) could 可以代替can，表示语气较为婉转Could you wait for me at the school gate?3) can和be able to 都表示能力，be able to 形式较多，并且表示成功地做某事。

He was able to flee Europe before the war broke out.= He managed to flee Europe before the war broke out= He succeeded in fleeing ----We shall be able to finish the work next week.4) 表示推测：否推：can’t be --, can’t have done--; 疑问推测：Can he be---?You look quite young. You can’t be forty. ( are you?)The light is still on. They can’t have gone to bed. (have they?)Can you be forty?What can they be talking about? （会在讨论什么呢？）Can he have written the book alone? （这本书会是他独自写的吗？）5) 虚拟could have done （本可以，原可以做）You could have come.6) 用在目的状语从句中He got up early in order that/ so that he could / might catch the early bus.II. may , might1)表示允许或征询对方许可，有“可以”意思，否定形式为may not (可以不)，但在表示“不可以”，“禁止”，“阻止”时，用must not.You may go now.May I watch TV after supper?Yes, you may. No, you mustn’t. 或No, you may not. No, you’d better not.在请求对方许可时，可用Might I---? 表示更礼貌。

2）表示可能性，有“或许”，“可能”意思。

可能性推测：may /might do---/ may/might have done---He may be right.He may/ might come today.He may/ might have missed the train.III. must, have to, ought to , should1)must 表示“必须”，“应该”，否定式must not, 不应该，不准，禁止。

Everybody must obey the rules.You mustn’t speak like that to your mother.Must I be home after 8 o’clock?Yes, you must. No, you needn’t.2)must 表示肯定推测（一定，必定，准是）must be/ must have doneYou must be hungry after the long walk, aren’t you ?He must have gone to Beijing, hasn’t he?He must have gone to the cinema last night, didn’t he?3) must 常有“偏偏” 的意思Why must you interrupt me now and then when I was talking?我在讲话时你为什么偏偏要不时地打断我?The telephone must ring when I was busy in the kitchen.我在厨房忙, 偏偏电话铃响了.4) must侧重说话人的主观色彩,而have to侧重表示客观情况限制不得不做的事We must empty the room so that we can get it painted soon.我们必须把房间搬空, 这样我们就能马上油漆.We have to empty the room because a couple will move in soon.我们得把房间搬空, 因为有一对夫妇户马上要搬进来.don’t have to do ---没有必要做--- You don’t have to worry about that.5) ought (not) to do --- 应该做---= should (not) do—You ought to/ should follow your father’s advice.should/ought to have done 该做而没做(含有责备之义)shouldn’t /oughtn’t to have done 不该做却做了(含有责备之义)He ought not to have kept us waiting so long.6) should 表示“万一”万一明天下雨，我们就不去动物园了．If it should rain tomorrow, we would not go to the zoo.Please take your umbrella in case it rains/ it should rain.7) 用在某些虚拟句型中suggest / order/ require / insist that sb. (should ) do—It is important/ necessary / essential --- that sb. (should ) do---8) should 有竟然的意思，还有推测的意思。

You can’t imagine that a well-behaved gentleman should be so rude to a lady. Mother should be back by now. 妈妈现在应该回来了。

IV. shall1)用于第二,三人称表示说话人的意愿, 如命令,警告, 威胁，允诺（陈述句）You shall have a new bike if you pass the exam. 允诺You shall do as I told you to. 命令2）在疑问句中，shall用来征询对方意见或请求指示，用于第一、三人称。

Shall he open the window?Where shall I wait for you?3)肯定句中，用于第一人称，表将来。

I will/shall telephone her tonight.V. will, would1) will 表示意志，意愿，用于各种人称。

I will tell you all about it.He won’t go.2)will 在疑问句中用于第二人称，表示征求对方的意愿，或向对方提出请求。

Will you go with me? Won’t you sit down?3)表示习惯性动作，有“总是”，“惯于”之义，（有一种发展趋势）Fish will die out of water.He will talk for hours if you give him the chance.The door won’t open.4)would 表示过去的意志，意愿They said that they would help us.5) would 比will婉转（指的是现在时间）I would like to see your new car.Would you like to see a film? Yes, I’d like to. Thanks. I am afraid I won’t be able to.6）过去的习惯动作When he was young, he would go swimming. ( used to)VI. need, dare既可以作情态动词又可以作实义动词1) need 在肯定句中只用作行为动词，否定句和疑问句中都可。

I need to go there at once. (行为动词)I need not do so.=I don’t need to do so.=I don’t have to do so.Need you do so?=Do you need to do so?Yes, I must. No, I needn’t. Yes, I do. No, I don’t.didn’t need to do=didn’t have to doneedn’t have done 本不必做----（言下之义做了）2）dare在肯定句中只用作行为动词，作为情态动词用于否定句和疑问句和从句中。

I dare to go home alone at mid-night.I dare not do so.= I don’t dare (to ) do so.If he dare do it, I will call for the police.VII. 总结情态动词的完成式。

needn’t have done 本来不必做却做了must have done 一定已经做了某事should/ought to have done 该做而没做shouldn’t /oughtn’t have done 不该做却做了could have done 本可以做却没做couldn’t have done 不可能做了某事might have done 也许做了某事。