英语语法(Unit21).pptVIP

英语语法 Unit 21 本单元学习要点 情态动词的概念和用法 不同情态动词表达类似意思 同一情态动词表达不同意思 Activity 1 （匹配句子：感受情态动词） 学习要点：情态动词的概念 1、属于助动词 情态动词属于助动词，必须和主要动词一起构成句子的谓语动词结构；不能单独使用（简答句除外）。 2、表达观点态度 情态动词除了有和助动词一样的语法功能外，还同时表达了说话时的观点或态度，所以被称作“情态动词”。 3、使用规则与助动词类似 用情态动词构成肯定句、否定句、疑问句等句型时，其功能和要求与助动词基本一致。 4、语气有轻重之分 由于情态动词是用来表达观点或态度的，所以存在语气上的轻重之分。 学习要点：情态动词一览表 学习要点：情态动词一般使用规则 1、无人称变化。例： I must do it! You must do it! He / She must do it! I can sing. You can sing. He / She can sing. 2、后接动词原形。 这点和助动词要求一样，省略to后以原形形式使用。例： You should go there now. I would call you again. They must be there. Can you help me? 3、构成的肯定式、否定式和疑问式（一般、特殊、反意与选择）的方法与助动词相同。 I can help you. I can not (cannot, can’t ) help you. Can I help you? What can I help you? You can’t help me, can you? You can help him or ask others to do it for you? Activity 2 （选择合适的情态动词填空并标注性质） 标记含义： Adv-忠告 Abi-能力 Per-允许 Pos-可能性 Ded-推断 Req-请求 Nec-必要性 1. (could, may) a. I’m having some trouble with this can-opener. Could you help me? (Req) b. You look like you’re having trouble with that can-opener. May I help you? (Per) 2. (should, will) a. If you want to speak English, you should practise as much as you can. (Adv) b. If you take this course, you will practice a lot of English. (Pos) 3. (ought to, can) a. You can buy batteries at any convenience shop. (Pos) b. You ought to use only alkaline （碱性的）batteries if you want your camera to last long. (Adv) 4. (must, should) a. These new regulations don’t make much sense. Must we follow them? (Nec) b. These new regulations don’t make sense. Should we try to get them changed? (Nec) 5. (must, might) a. I can’t find my umbrella. I must have left in the office. (Ded) b. You should take an umbrella. It might rain. (Pos) 学习要点：情态动词过去式的语气效果 情态动词从现在时态向过去时态转换，会产生两种语气效果： 1、委婉 凡是用过去式的情态动词构成的语句，其语气都很委婉。例： I can’t do it like that! / I couldn’t do it like that! You shall clean it. /