和 用法的区别,Presented by*,can,be able to,它们用法上的不同主要体现在以下几方面:,1. can只有两种时态, 即can 和could;而be able to 有多种时态, 如was/were able to, will/shall be able to, have/has been able to等。 e.g. Ill be able to drive the car in a week. Through his diligent work, the deaf-mute has been able to read and write in a sign language.,2.表示过去通过努力终于做成了某事要用be able to，而不能用can。 can 和be able to 都可以表示能力.can泛指一般的能力, be able to 则主要指具体做到了某件事的能力.,I can swim. I am able to swim. () () All the people could escape from the big fire in time. All the people were able to escape from the fire in time. ()(),3.can能表猜测，be able to不能。can的这种用法主要用于疑问句和否定句。其肯定形式是must be。,e.g. Somebody is knocking at the door. Who can it be? It cant be our teacher who is knocking at the door. It must be our teacher who is knocking at the door.,4can 可以表 “允许”, 与may可以互换, 此时不能用be able to 代替。如： “Can / May I sit here？” 由于may not 有两个意思, 即 “不可能” 和 “不许可”, 在口语中，表达这两种不同的含义是通过句重音来解决的。,He may not go home this weekend. He may not go home this weekend. (I dont permit him to go home this weekend.) He may not go home this weekend. (He will probably not go home this weekend.),而在书面表达时不可能使用句重音的手段, 所以最好用cant代替may not来表示 “不可能”： He cant go home this weekend.,5. can 是情态动词，只能用作谓语成分，be able to是普通动词短语，既可以作谓语，也可以作非谓语。,Being able to speak English fluently, he has no difficulty in communicating with the Americans at the party. How I long to be able to communicate with the foreigners in fluent English!,