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　　情态动词有一定的词义, 表示某种感情或语气, 是不完全动词, 不能单独作谓语, 需和实义动词一起构成谓语. 常见的情态动词有: can / could, may / might, must, shall / should, will / would, need, ought to, dare / dared等
　　一.may / might的用法:
　　1.表示“可以”, 即表示说话人许可或请求许可
　　a. You may take it away.
　　b. May I come in ?
　　2.表示“可能, 也许” (在疑问句中通常不用may / might, 而用likely, do you think, can等表示“是否可能, 会不会”的意思)
　　a. He may come today.
　　b. Is it likely to rain ?
　　c. Do you think the train will be late ?
　　d. Can the news be true ?这消息会是真的吗?
　　3.在提建议时, 可用May I … ?
　　a. May I carry your bag ?
　　b. May I make a suggestion ?
　　二.can / could的用法:
　　1.表示许可或请求许可, 相当于may. 但can比may用得更广泛. can不仅表示说话人同意, 准许, 还可以表示客观条件许可. may通常只表示说话人同意或准许
　　a. The class is over. You can go home now.
　　b. You can go there tomorrow.
　　c. Can I borrow your car for today ?
　　2.在提建议时, 可用Can I / you… ?
　　a. Can I buy you a drink ?
　　3.表示“会, 能”, 相当于be able to
　　a. He can speak English.
　　b. Can you play tennis ?
　　c. Little Tom can’t move the big box.
　　4.在疑问句中表示怀疑, 不确定或不会有的情况, 即“否定的推测”
　　a. Can it be true ? 这是真的吗?
　　b. Can it be true that he has passed the exam ? 他真的通过考试了吗?
　　5.can’t / couldn’t在陈述句中可表示“肯定不, 一定不”的意思
　　a. He can’t be in the room right now.
　　b. It can’t have rained last night, for the ground is dry.
　　6.can’t / couldn’t help doing sth表示“不得不,忍不住做某事”
　　a. People couldn’t help laughing at the foolish emperor.
　　7.can / be able to do的区别:
　　①.be able to可用于各种时态, 而can只有现在时can和过去时could
　　②.be able to可以和另一个不完全动词连用, 如should be able to (应该能够), must be able to (必须能够)等, 而can则不可以这样用
　　③.强调“能力”时, 多用be able to
　　a. The patient was soon able to sit up and read.
　　④.can可用于人或其他事物作主语的句子中; be able to只用于有生命的名词或代词作主语的句子中
　　三.must的用法:
　　1.表示“必须”, 它的否定形式是need not / needn’t, 而不是must not / mustn’t, mustn’t表示禁止或不许做某事
　　a. You must set off at once.
　　b. You needn’t tell John about it.
　　c. You mustn’t play with fire.
　　2.表示“肯定是, 一定是”的推测意义; 与此对应, 表示“肯定不,一定不”用can’t, 而不用mustn’t
　　a. You must be very tired now.
　　b. If he had really been there, I must have seen him.
　　c. He must have gone away. We don’t see him anywhere.
　　3.must / have to的区别:
　　①.must / have to一般可以通用, 但must侧重于说话人主观上的看法, 即“说话人认为必须”; have to侧重于客观上的需要, 含有“客观上不得不”之意
　　a. If the person is not breathing, you must try to start his breathing.
　　b. You must / have to study with a teacher if you want to know how to do first aid.
　　②.must没有时态的变化, 一般用于表示现在或将来; have to有时态的变化, 可用于过去, 现在, 将来各种时态
　　a. We must study hard when we are young.
　　b. I think she must remain in hospital for a week.
　　c. We had to stay there for a whole day because of the rain.
　　d. We have to practise a lot if we want to speak English well.
　　e. The situation has changed; we will have to change our plan.
　　③.它们的否定式mustn’t / not have to有很大的不同: mustn’t表示“不要(做某事)”, 有禁止之意; not have to表示“不必要(做某事)”, 含有“客观上无此必要”之意
　　a. You mustn’t move a person if he is badly hurt.
　　b. You don’t have to be a doctor to do first aid.
　　四.would的用法:
　　1.表示主观意志和愿望, 即“愿意,想要”
　　a. Come here whenever you would.
　　b. He would not leave before he finished his work.
　　2.would do sth可以表示过去经常发生的动作, 相当于used to do sth
　　a. When we were children we would go swimming every summer.
　　b. On Sundays he would go fishing for hours when he lived in the countryside.
　　3.表示请求, 愿望, 语气客气, 委婉
　　a. I would like some tea.
　　b. Would you mind closing the door ?
　　c. Would you tell me something about your trip ?
　　4.表示推测, 表示“大概, 也许”的意思
　　a. That would be the pen you are looking for.那也许是你在找的笔吧
　　五.should的用法:
　　1.表示义务, 责任, 可译为“应当”
　　a. We should complete the text in time.
　　b. You should be so careless.
　　2.表示推测或推论, 可译为“可能, 应该是”
　　a. He should be home by now, I think.
　　b. He should have arrived in Nanjing by this time.
　　3.should / ought to的区别:
　　should / ought to一般可以通用. should侧重于说话人主观上的看法, 有时含有劝告, 建议的口气, 即 “按我的想法应该如何”; ought to语气更强, 强调“有责任, 有义务做某事”或者 “按道理应该如何”
　　a. “I will start the work at once.” “I think you should start at once.”
　　b. “I will start the work tomorrow.” “No. You ought to start at once.”
　　六.need的用法: need表示“需要”, 既可作为情态动词, 也可作实义动词
　　1.need作实义动词时, 注意以下用法:
　　①.need to do sth; ②.need sb to do sth; ③.need doing sth (主动形式表被动意义)
　　a. You need to remain in bed.
　　b. I need you to help me with the housework.
　　c. The garden needs watering.( =The garden needs to be watered.)
　　2.need作情态动词时, 多用于否定句及疑问句中, 不用于肯定句中
　　a. It is still early. You needn’t hurry. =You don’t need to hurry.
　　b. It is 11 o’clock. Need I go now? =Do I need to go now ?
　　3.对于用need的提问, 肯定回答用must, 否定回答用needn’t
　　a. Need I come? Yes, you must. / No, you needn’t.
　　七.dare / dared的用法: 表示 “敢”, 既可作为情态动词, 也可作为实义动词
　　1.作为情态动词时, 主要用于否定句和疑问句中, 不用于肯定句中
　　a. Little Jane dared not go alone. =Little Jane didn’t dare to go alone.
　　b. Dare you go out alone at night ? =Did you dare to go out alone at night ?
　　2.作为实义动词时, 可用于: dare to do sth
　　a. Little Jane didn’t dare to go alone.
　　b. Did you dare to go out alone at night ?