情态动词 一、can和could的用法 1．表示能力 Her mother can speak French. 2．表示客观可能性 Anybody can make mistakes. 3．表示许可(多用于口语) Can I go now? 4．表示惊异、怀疑、不相信的态度(主要用于否定句、疑问句或感叹句中) How can you be so careless! 你怎么会那么粗心！ 5．can的特殊用法 can but只有；can't but不得不；can't...too再怎样也不为过，越……越好。 I can but wait.我只有等待。 I can't but wait.我不得不等待。 You can't be too patient to the customers.你对顾客越耐心越好。 二、may和might的用法 1．表示允许、请求 —May I watch TV now? —Yes，you may.(Yes，please.) —No，you mustn't.(No，you'd better not.) 2．表示可能性(主要用于陈述句、肯定或否定句，疑问句用can代替) The story may not be true. 3．表示祝愿(不用might) May you succeed! 4．may/might as well最好还是…… You might as well do it now. 5．may/might well很可能 He may well be late for class. 三、must，have to和ought to的用法 1．must (1)must表示“必须，应该，一定要”。强调主观看法，只有现在时形式，否定式是must not(mustn't)。must开头的问句，其否定回答要用needn't或don't have to代替。 (2)must表示必然的结果。 All men must die.人都会死(是自然规律)。 (3)must还可表示主语固执、偏要做他人不希望做的事。 It can't help；he must do that. 2．have to着重客观需要，能用于更多时态(过去时或将来时)。 He will have to be there before ten. 3．ought to表示义务和责任，“应该”，比should语气要强。 You ought to take care of yourself. 四、need和dare的用法 1．need表示“需要，必要”，只能用于否定句和疑问句。在肯定句中，常用must和have to代替。 2．dare表示“敢”，通常用于否定句、疑问句和条件状语从句中。 Dare you go home alone at eleven in the evening? 3．need和dare的特殊用法 (1)need表“需要”时，可用want，require代替。 The desk needs to be repaired./The desk needs repairing. (2)dare作实义动词时，在肯定句中要接to，在疑问句和否定句中to可省去。 He dares to catch a snake. 五、will和would的用法 1．will (1)表示请求、建议，常用于第二人称。 Will you please go with me? (2)表示意愿、决定、允许。 I will never do that again. (3)表示习惯性动作或某种倾向，“总是，惯于”，通常用于第三人称。 Fish will die out of water. 2．would (1)表示请求、建议，比will委婉，指现在时间，多用于第二人称。 Would you like a cup of tea? (2)表示过去习惯性动作或某种倾向。 We would play badminton on Sundays. 六、shall和should的用法 1．shall (1)用于第一、三人称，在问句中表示征求对方意见或请求。 (2)用于第二、三人称表示命令或威胁。 You shall do as your father says. 2．should (1)表示责任、义务，意为“应该”。 (2)表示惊讶语气，意为“竟然”。 You should wear slippers in class.
(3)用于条件句，表示“假如，万一”，省去if，should可提至句首。 Should you be late，apologize to the teacher. 七、“情态动词＋have done”的用法 1．must have done sth.；can(could) have done sth. (1)must have done sth.表示对过去已经发生的事情的有把握的推测，意思是“想必、准是、一定做了某事”，只用在肯定句中。 It must have rained last night，for the ground is wet.
(2)can(could) have done sth.表示对过去发生的动作的怀疑和不肯定，通常用在否定句和疑问句中。 He can't have forgotten it.他不可能忘记的。 2．needn't have done sth.；didn't need to do sth. (1)needn't have done sth.表示已完成不需要完成的动作。 You needn't have waken me up.I don't have to go to work today. (2)didn't need to do sth.表示没有必要做而实际上也没有做某事。 I didn't need to clean the windows.My brother did it. 3．may/might have done sth. may/might have done sth.表示对过去已发生的动作的推测，意为“也许/或许已经……”。 I'm not sure.He might have said so at the conference.
4．should have done sth. should have done sth.表示本来应该做某事而实际上未做。 You should have told him about it.