情态动词的特点19p.pptVIP

Grammar: Modal verbs Lectured by RenQiuyu 一、情态动词的特点 1 有词义 2 没有人称和数的变化。也就是说，它在任何主语后形式都是一样的，这是情态动词和助动词最大的差异。 3 有时态的变化 4 不能独立作谓语，后面必须跟动词原形 在情态动词后一般要跟不带to的不定式（ought to除外） 二、情态动词的种类 1) can表示体力、智力上的能力。否定式为cannot, 缩略为can’t; 过去式为could couldn’t eg: We can do things they can’t do. Mary can type well and her mother could type well when she was young. 2) 表示客观可能性 eg: Man cannot live without air. 3) 表示征求意见或请求许可，表示语气委婉 eg: Can I go for a swim this afternoon, Mum? Could you lend me your bicycle? No, sorry, I can’t. ( couldn’t is wrong) Yes, of course you can. 4) can 和could 表推测（can用于否定及疑问, could肯定、否定、疑问皆可） can (could) not + V原（link.或状态动词）对现在状态的推测 can (could) not + be + doing对现在动作的推测 can (could) not + have done 对过去动作的推测 eg: a. The young girl can’t be our new chairman. Can/ Could the news be true? b. He can’t be reading in the reading room, for I saw him in the street just no They may be arguing. But I am interested in what they can/ could be arguing. c. The road isn’t wet. It can’t/ couldn’t have rained last night. I don’t know why she didn’t call me yesterday. Can/ Could she have forgotten my telephone number? 5) could have done本能做却没有做, can have done这种结构不存在 eg: You could have caught the first train, but you got up too late. 6) Can/ could与 be able to 的区别 A. be able to do sth.也表示能力，可以用于不同时态，前后还可以用情态动词must, may, might以及seem to, used to, appear to等，而can/could只用于一般现在时和一般过去. eg: He is able to (= can) play the piano very well. After three years of hard work, he was able to pass the entrance examination. The large hall will be able to hold 5000 audience. He seems to be able to work out the puzzling question. B.当用于过去时态时，could表示能力，但有没有做，不知；而was/were able to 指过去某种具体的能力，通过努力并做成功了，相当于managed to或succeeded in eg: He could sing many English songs. It’s known that he was able to recite many foreign poems at six. 1) may表示请求许可。疑问式May I....?多为请求允许，通常用于正式文体 eg May I come in? No, you can’t / may not