Unit 2 Sports events情态动词（）概念引入The classroom can seat thirty students. 这教室能坐三十位学生。 You must obey the school rules.你必须遵守校规。It is cold in the room. They must have turned off the heating. 屋里很冷，他们肯定把暖气关了。It must / may / might / could have rained last night .The ground is wet. 地湿了，昨晚肯定/可能/也许下雨了。注意这些句子中的斜体词部分，都是情态动词，这些情态动词看着很熟悉，但是也有点陌生，如后两个句子中与have done连用。究竟哪些词属于情态动词呢？它们各自都有什么用法呢？为什么情态动词有时需要与have done连用呢？从此单元开始，我们就小结一下情态动词的用法。语法讲解概念及shall/should概念在动词(一般动词)之前形成动词的否定,疑问,时态,语态,语气或表示特殊意义的动词叫做助动词,其中具有感情色彩一些助动词叫做情态动词。 分类: be动词, have, do；-助动词shall, should, will would, can, could, may, might, must, ought, need, dare, used和had better. -情态动词例如：-What was the something you saw? 你看见的是什么？-I, I couldnt say. 我不能说。-You couldnt say or you wouldnt say? 你不能说还是你不愿意说？情态动词是一种本身有一定的词义，但要与动词原形及其被动语态一起使用，给谓语动词增添情态色彩，表示说话人对有关行为或事物的态度和看法，认为其可能、应该或必要等。情态动词后面加动词原形。shall 1. shall在纯表示将来的陈述句中只用于第一人称。 2. 在问句中征求对方的意见和指示的时候常用于第一、三人称。 Shall I post your letter for you?Shall we carry your baggage?Henry is waiting outside. Shall he come in?3. 用于第二、三人称，表示说话人的许诺、命令、警告、威胁或允诺等。 Tell Jerry that he shall get a gift if he is nice.You shall be punished for what youve done. should 1. 构成过去将来时作为shall的过去时。He asked me whether I should be free tonight.2. 表示主语的义务或责任。 You shouldnt eat between meals, for it will make you fat. 3. 表示很大的可能性，常译为“按道理说应该”。 There should be a double “m” in the word swimming.4. 用于否定句、疑问句表示“竟然”，含意外、惊异、愤怒、失望等语气。Why should you be so late today?I dont understand why you should think that I did it.5. 在if 从句中表示“万一”。Ask Tom to ring me up if you should see him.6. 重要句型：should have done 表示过去没有做到本来应该做的事情shouldnt have done 做了本来不应该做的事情You should have given him more help.You shouldnt have left home without saying a word.can/could（could是can的过去时）(1)表示能力。如：He can speak English better than you. can和be able to都可表示能力，两者在意思上没有什么区别。但是can只能有现在式和过去式could，而be able to则有更多的形式，可位于情态动词之后表达过去成功地做了某事。如：He will be able to do the work better.He was able to finish the work on time.(2)表示客观的可能性，也可以表示一时的情况，意为：有时候会。Accidents can happen to any drunken driver.According to the radio, it could rain this afternoon.It can be very hot here in summer.(3)表示“许可”时can可以和may换用，如：如果要表示语气婉转，可用could代替can，这时could不再是can的过去式，注意回答时不能用could，而用can。You can (may) go home now. - Could you come again tomorrow?- Yes, I can./ No, I cant.(4) 在疑问句和否定句中表示推测、怀疑、惊奇、不相信的态度。如：Can this green bike be Liu Dongs? How can you believe such a liar like him?(5) could have done有虚拟的含义，即“本来能够做，但事实上却没有做”。例如：You could have told me earlier.I could have helped her.I could have passed the exam if I had worked harder.may/might (might是may的过去式)(1)表示允许或许可，否定用mustnt, 表禁止。如：-May we swim in this lake? -No, you mustnt. Its too dangerous. 肯定可以用比较婉转的说法进行回答。如：- May I use this dictionary? - Yes, please. /- Certainly. / Yes, you can.(2)在表示请求时，用might比may 语气更婉转些, 如：May I have a look at your new computer? 注意：May I?在文体上较正式，较客气，日常口语中常用Can I?(3)may或 might都可以表示可能性，表示“或许”、“可能”之意，might表示语气更加不肯定，如：They may (might) be in the library now .He is absent. He may/ might be ill.The person who sets out late might be careless in driving.(4) may have done表示“某一事件在过去发生的可能性”。如：Why hasnt she come?She may have missed the train.另外，might have done还有虚拟的含义，表示“与事实相反”。如：You were stupid to try climbing up there. You might have killed yourself.(5) May用于祈使句，表示祝愿。如：May you have a happy life.May you succeed.比较：Wish you a happy new year. Wish you success.must和have tomust(1)must表示“必须”、“应该”之意，语气比should, ought to强烈， 其否定式 must not，缩写形式为 mustnt，表示 “不准”、或“禁止”之意，如：We must study hard and make progress every day. You mustnt touch the fire. (2) 对以must提出的疑问句，如作否定回答时，要用neednt或用dont (doesnt) have to (不必)来回答，而不用mustnt，因为mustnt表示的是“禁止”或“不许可”之意，如： - Must we finish the work tomorrow? - No, you neednt (dont have to), but you must finish it in three days.(3) must可以表示推测，表示“一定”或“必定”之意，只用于肯定句中。如：- Whose new bike can it be? - It must be Liu Dongs. I know his father has just bought him a new one.You must be ill. I can see it from your face.(4) must have done 用于对过去或已经完成的事情的推测。must be doing 用于对现在正在进行的事情的推测。It must be raining outside. 外面一定在下雨。He must have gone over the article, hasnt he? 你已经浏览过这篇文章了，是吧？have to (1)have to和must的意义相近，只是 must侧重表示说话人的主观看法，而have to 则表示客观需要，如：I must ask you not to do that again. 我必须要求你再也不要那么做了。 Son, if you want to catch a fish, you have to think like a fish.孩子，如果你想要抓住鱼，你必须像鱼一样思考。You have to hand in your compositions before next Monday.(2)have to 有人称、数和时态的变化,否定式要用助动词，如dont have to：They had to speed up, for the weather turned terrible. He has to stay at home because of illnesswill和wouldwill的基本用法(1) 可以表示“意志”或“决心”，如：I have told him again and again to stop smoking, but he will not listen. Can someone help me? I will.(2) 请求或询问对方的意愿，如：Will you please tell me how to ge