英语语法第八讲情态动词.ppt

语法专题复习,第八讲情态动词,1can(could)，be able to can只有现在式和过去式could两种形式，be able to可用于现在式、过去式、将来时、完成时。要表示“能够做某事”，可用can或be able to，但若要说过去的确运用了某种能力做成了某件事情，就只能用was/were able to，表将来具备的能力只能用will/shall be able to.(1)If you study hard，you will be able to express freely in English in three months.(2)The fire spread through the hotel very quickly but everyone was able to get out.,2could是can的过去式，但是在很多情况下，特别是在口语中，它表示语气的委婉。因此，用could提问时，不能用could回答，而要用can或may。would、might用于疑问句时也表委婉语气，回答时应该用will，may。(1)Could I borrow your dictionary?Yes，of course you can.(2)Could I call you by the first name?Yes，you may.(3)Would you be so kind as to explain the word?Yes，I will.What is it?,3may/might，can/could都可表可能，但may/might 不能用于问句，can/could用于否定句、疑问句、感叹句，表示惊异、怀疑，一般不用于肯定句。如果用于肯定句，则表示偶尔发生某事的可能，或某人某物一时的特点。(1)Are you coming to Jeffs party?Im not sure.I might go to the concert instead.(2)Where can Mr.Li be?Sorry，I dont know.You can go to ask Mr.Zhang.He may help you.,(3)Mr.Bush is on time for everything.How can it be that he was late for the opening ceremony?(4)We enjoy good weather in January，but sometimes it can be terribly cold.(有时偶尔也会很冷),4must表推测用于肯定句，其否定式要用cant.对现在表示推测：must do，cant do对正在进行的动作表示推测：must be doing，cant be doing对过去表示推测：must have done，cant/couldnt have done.,(1)There were already five people in the car，but they managed to take me as well.It couldnt have been a comfortable journey.(2)Jack cant have arrived yet，otherwise he would have telephoned me.(3)Put on more clothes，you must be feeling cold with only a shirt on.(4)I didnt hear the phone.I must have been asleep,5情态动词完成体的意义can/could have done过去可能做过，过去本来可以做某事但没有做must have done过去一定做过may have done可能已经做过，本来可以做但没做might have done过去可能做过，过去本来可以做但没做cant/couldnt have done过去不可能做过某事should(not)have done过去本该(不该)做，但却没做(做了)ought(not)to have done过去本该(不该)做，但却没做(做了)neednt have done过去本来没必要做，但却做了would rather(not)have done宁愿过去做了(没做),注意：must have done，may have done，might have done，cant have done都表推测。其区别在于可能性的大小。must have done表很有可能，may have done表有可能，might have done表可能性很小，cant have done则为“不可能”。(1)I told Sally how to get here，but perhaps I should have written it out for her.(2)Sorry，Im late.I might have turned off the alarm clock and gone back to sleep again.,(3)I was really anxious about you.You shouldnt have left home without a word.(4)Tom neednt have got up that early since it was Sunday and he had nothing important to do.(5)I would rather not have blamed him because he was a child after all.6关于should的主要用法(1)Its already seven oclock.Jack should be here at any moment.(should表推测，意为“随时都会来”、“真该来了”。),(2)When can I come for the photos？I need them tomorrow afternoon.They should be ready by 1200.(should应该)(3)You cant imagine that a well-behaved gentleman should be so rude to a lady.(should表惊异，意为“居然”，“竟然”)(4)If he should fail to come，ask Mr.Zhang to attend the ceremony instead.(should表语气较强的假设，意为“万一”)(5)We should have studied last night，but we went to the concert instead.(should本应该),7关于shall的用法shall用于第一人称、第三人称疑问句中，表示说话人征求对方意见或向对方请示。shall用于第二、第三人称，表示说话人给对方的命令、警告、允诺或威胁。(1)Shall I go on reading the text?我要继续读课文吗？(shall征求意见)(2)You shall be punished one day for what youve done.总有一天你会因你的所作所为得到惩罚的。(shall 威胁，警告)(3)He shall get what he deserves.I promise it.他会得到他应该得到的，我保证。(shall允诺),祝,您,学业有成,