情态动词现现在式过过去式否定式 一般 情态态 动词动词cancouldcannot / cant; couldnt maymightmust not / mustnt may not; might not cannot / cant; couldnt mustmustneed not / neednt must not / mustnt shallshouldshall not / shant; shouldntwillwouldwill not / wont; wouldntneed/need not / neednt短语语 情态态 动词动词be able towas / were able tobe not able tohave / has tohad todont/doesnt have to; didnt have to used toused not to / didnt use toought to/ought not to / oughtnt toexercise1） 情态动词不能表示正在发生或已经发生的 事情，只表示期待或估计某事的发生。 2） 情态动词 除ought 和have 外，后面只能 接不带to 的不定式。 3） 情态动词没有人称，数的变化，即情态动 词第三人称单数不加-s。 4） 情态动词没有非谓语形式，即没有不定式 ，分词，等形式。 备注：情态动词无人称和数的变化；不能单 独使 用，必须与其后的动词原形构成谓语 一、 can, could 1) 表示能力（体力、知识、技能） Can you lift this heavy box?（体力） Mary can speak three languages.（知识） Can you skate?（技能） 此时可用be able to代替。Can只有一般现在时和一般过去式； 而be able to则有更多的时态。 Ill not be able to come this afternoon. =I cant come this afternoon.当表示“经过努力才得以做成功某事”时应用be able to，不能用 Can。如： He was able to go to the party yesterday evening in spite of the heavy rain. 2) 表示请求和允许。 -Can I go now? - Yes, you can. / No, you cant. 此时可与may互换。在疑问句中还可用could, might代替，不是过去式，只是语气更委婉，不能 用于肯定句和答语中。 - Could I come to see you tomorrow? - - Yes, you can. ( No, Im afraid not. ) 3) 表示客观可能性（客观原因形成的能力）。 There is still a lot of time, so we can go by bus. This hall can hold 500 people at least. 4) 表示推测（惊讶、怀疑、不相信的态度），用于 疑问句、否定句和感叹句中。 Can this be true? This cant be done by him. How can this be true? 二、 may, might 1) 表示请求和允许。might比 may语气更委婉，而 不是过去式。否定回答时可cant 或mustnt，表示“不可以，禁止”。 Might/ May I smoke in this room? No, you mustnt. May/Might I take this book out of the room? Yes, you can. (No, you cant / mustnt. ) 用May I.？征徇对方许可时比较正式和客气，而用 Can I.？在口语中更常见。 2）用于祈使句，表示祝愿。 May you succeed! 3）表示推测、可能性（不用于疑问句）。 might不是过去式，它所表示的可能性比may小。 1He may /might be very busy now. 2Your mother may /might not know the truth. 三、 must, have to 1) 表示必须、必要。 You must come in time. 在回答引出的问句时，如果是否定的，不能用 mustnt（禁止，不准），而用neednt, dont have to（不必）. Must we hand in our exercise books today? Yes, you must. No, you dont have to / you neednt. 2) must是说话人的主观看法， 而have to则强调客观 需要。Must只有一般现在时， have to 有更多的时态 形式。 1 he play isnt interesting, I really must go now. 2 I had to work when I was your age.3) 表示推测、可能性（只用于肯定的陈述句） 1 Youre Toms good friend, so you must know what he likes best. 2 Your mother must be waiting for you now. 四、兼做情态动词和实意动词的need (1) 在疑问句和否定句中可作情态动词或实意动词Need you do so? / Do you need to do so?You neednt do so. / You dont need to do so. (2) 在肯定句中只能作实意动词You need to do so. He needs to do so. (3) need 作情态动词 + 动词原形作实意动词 + to+v. / + n. / + ving The little girl needs some help. The old lady needs to look after the baby. The old lady needs looking after well. = The old lady needs to be looked after well. 练习： 1. _ I water the trees on Tuesday? No, you neednt. A. Can B. Must C. May D. Shall 2. _ you come to my party? Certainly! Id love to。A. Must B. Should C. Can D. Might 3. Will you answer the phone? It _ be your mother.Sorry, I _. Im busy.A. can, mustnt B. will, cant C. may, cant D. need, will 4. May I smoke here? No, you _ only do that in the smoking room.A. can B. need C. mustnt D. couldnt 5. Will you come to my party? Sorry, But I _ look after my little brother.A. need B. have to C. can D. couldBCC