5情态动词用法不定式.docVIP

4.“情态动词+不定式”的用法 1)“can(could)+have done”的肯定式表示“本来可以做而实际上未能做某事”，疑问或否定形 式表示对过去发生的行为怀疑或不肯定。例如： You could have done better，but you didn’t try your best． He cannot have been to that town． Can he have got the book? 2)“may(might)+have done”表示对过去发生的行为的推测。例如： He may not have finished the work． If we had taken the other road，we might have arrived earlier． might所表示的可能性比may弱，语气较委婉。 3．)must+have done的结构常用在肯定句中，表示对过去发生的行为的推测，意为“一定，想必”。它的否定或疑问形式用can代替must。例如： It must have rained last night，for the ground is wet． He must have been to Shanghai． 4)needn’t+have done”表示本来不必做某事而实际上做了某事。例如： You neodnt have watered the flowers，for it is going to rain． 注意：didnt need to(have to)do指“没有必要做而实际上也没有做某事”。例如： I didn’t need to clean the windows because my sister had done it． 5)“should+have done”表示本应该做到而实际上没有做到。其否定式表示某种行为不该发生但却发生了。例如： You should have started earlier，but you didn t. He shouldnt have cheated in the exam． 注意：He should have finished the work by nOW．(表示推测) 6)“will。+haye done”的结构表示推测，主要用于第二、三人称，表示对已经完成的动作或事态的推测。例如： He will have arrived by now． 7)“ought to+have done”表示过去应做某事而实际未做。例如： You ought to have helped him(but you didn’t)． 这时，ought to与should可以互相换用。 9.used to,had better, would rather的用法 1)used to表示过去的习惯动作或状态(现在已不复存在)，在间接引语中，其形式可不变。例如： He told us he used to play football when he was young． 在疑问句、否定句、否定疑问句或强调句中，可有两种形式： Did you use to go to the same school as your brother? 疑问句 Used you to go to the same school as your brother? I usedn’t to go there． 否定句 I didnt use to go there． usedn’t亦可拼作usent，但发音皆为【ju：snt】。 否定疑问句Usen’t you to be interested in the theatre? Didn’t you USe to be interested in the theatre? 强调句I certainly used to smoke，but it was a long time ago． I certainly did use to smoke，but it was a long time ago． 其反意疑问句或简略回答中，也有两种形式： she used to be very fat，didn’t she? use(d)n’t she? -Did you use to play chess?-Yes，I did