情态动词 用法 举例表示能力，意为“能、会” I can play the guitar. I cant play the violin.表示允许， “可以” ，Can I?意思是“我可以吗？”较口语化。 Can I go home now? / You can tell him about that now.Can表示可能性， “可能” （推测） ，常用在否定句和疑问句中，其中 cant表示“不可能” ，其肯定回答用may或 must.-Where can it be? It may/must be in your desk. Miss Gao cant be at home now.Can的过去式，表示过去的能力。 She said that she could go./Lucy could swim at the age of five.表示较 can更为委婉的语气。- Could I come to see you tomorrow?- Yes, you can. ( No, Im afraid not. ) Could you tell me something about Tibet?could虚拟语气 I wish I could go some day.be able to 有 4中时态 一般现在时、一般过去时、一般将来时、过去将来时表示允许、请求。比 can 正式 You may go now.May I help you?回答以 may 开头的疑问句有如下表达法： -May I smoke here? 我可以在这儿抽烟吗？-Yes, you may. / Yes, please. 请抽吧。 -No, you cant. / No, you mustnt. / No, youd better not. 请不要抽烟。表推测,常用语肯定句中。 He may be at home He may go abroad It may not be true、may表祝愿（不用 might） May you success May you be happymight 表示过去 He asked if he might look at my new shirt.表示必然性、必须（主观） You must stay at home。You mustnt Smoke here。Must I hand in the paper? Yes, you must/no, you neednt /dont have to(区分 have to)must表推测，只用于肯定句中。 He must be at home I must have fallen asleep. (对过去的肯定推测)have to 只好、不得不（客观的必须，有时态和人称的变化） My mother is ill, I have to look after her at home.用于第一人称表示将来时，助动词 I shall（will ）speak at the meeting tomorrow （表示单纯的将来）征求意见用于一三人称疑问句，情态动词 Shall we start to work？（表示征求对方的意见）When shall we leave for Beijing?shall用于二、三人称，表示说话人的允诺、命令、威胁。 You shall get the answer tomorrowshould 表示劝告、建议、义务，意思是“应该” 。 We should say sorry to her.表将来时时，用在一、二、三人称中 I will never do that again.用于第二人称的疑问句中,表示请求、建议。 Will you help me carry the box?will表示预料或习惯性的动作。 Fish will die out of water.表示过去 When we were children,we would go skating every winter.would 采用虚拟语气，但不提条件，语气委婉，表示要求、邀请、希望或询问，后接 like/love/mind 等动词。比 will更委婉。Would you like a cup of coffee? Would you please show me the way?(省略了 If I could ask you,比用 will客气的多。)行为动词，肯定句中，后跟 to.借助于助动词。 You need to change your habits.need情态动词，否定、疑问、条件句中 I neednt clean the windows. Need I tell her mother about it? Yes,you need./No, you neednt.行为动词，肯定句中，后跟 to.借助于助动词。 The girl did not dare to go outside alone at night.dare情态动词，否定、疑问、条件句中 He dare not ask him about the matter. Dare she stay at home alone? If he dare say such thing,I will never talk with him.ought to 表示义务与责任 You ought to take care of your parents. You oughtnt to spit anywhere. Ought I to go? Yes,you ought (to).No,you neednt.used to 表示过去常常 They used to have more delicious food. They didnt used(used not,usent) to have more delicious food. Used they to have more delicious food. There used to be a school, usednt there?had better 表示“最好” ，建议或劝告，缩略：d better Youd better send for a doctor. Youd better not go there alone.