第2讲 情态动词和虚拟语气 情态动词 1．情态动词can和could的用法 语法规则 例句 表示“能力”时，can表示现在的能力，could表示过去的能力 Susan isn't very good at maths, but she can speak English very well． I could swim when I was five years old． 表示“推测”时，can常用于否定句中，can't表示“不可能”；could表“推测”时，比can的可能性要小 Mr Black can't be at home—he has gone to America． Even experienced teachers can make mistakes． 表示“请求”或“许可”时，通常用于疑问句中；could表“请求”时，语气比can更委婉 —Could/Can you pick me up at the airport —Yes, I can． be able to do表示“能够做”，不能与 can连用，但有更多时态 I'm sure you will be able to look after yourself． I haven't been able to sleep very well recently． 2．情态动词may和might的用法 语法规则 例句 may和might可用于肯定句中表示“许可”，用于疑问句中表示“请求” She said I might call her at the weekend． May I borrow the car tomorrow？ might表示“推测”时，可能性比may的可能性小 He may/might know the answer． He may/might not believe you． may/might well do sth．表示“很可能做某事”，may/might as well do sth．表示“不妨做某事” Her appearance has changed so much that you might well not recognize her． You might as well give him the letter． “May you/sth．＋动词原形”表示祝愿 May you succeed! May all your dreams come true！ 3．情态动词must和have to的用法 语法规则 例句 must强调说话者主观上认为某事是必须做的，着重个人的看法、责任或义务。have to强调由于客观条件、外界因素等迫使某人不得不做某事 You must finish your homework before you go to bed． I missed the bus, so I had to take a taxi． 4．情态动词will和would的用法 语法规则 例句 will表示“请求”，常用于第二人称的疑问句中，would比will语气更委婉 Will you join our discussion Would you open the window, please？ will表示主观愿望、意志或决心，would用于过去的习惯性动作，意为“过去常常做某事” Go where you will． She asked if I would go with them． On summer evenings they would sit out in the garden． will和would用于第二人称的疑问句中，would表示委婉语气 Wouldn't you take off your coat Would you please post the letter for me？ would用于否定句，可以表示顽固倾向，意为“老是不，总是不” My car wouldn't start this morning． The door wouldn't open, no matter how hard she pushed． would have done表示与过去事实相反的假设 But for your help we would have been late． If she had seen you yesterday, she would have asked you about it． 5．情态动词shall，should和ought to的用法 语法规则 例句 shall用在第一、三人称的疑问句中时，表示征求对方意见 Shall Tom go there with me tomorrow shall用在第二、三人称的陈述句中时，表示说话人的允诺、命令、告诫等 You shall get an answer from me tomorrow． should/ought to表示责任、义务，意为“应该”，否定式为should not/ ought not to You shouldn't be so careless． Humans ought to stop polluting nature． Ought I to hand in my composition now？ should表示“推测”，常意为“按道理说应该” It should be Mike who has taken away all the materials． should可以表示说话人的吃惊、愤怒、失望等，多用于It is＋形容词＋that...句型 It's surprising tha ... ...
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