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1、1 第三讲 情态动词一. 情态动词的定义 : 英语中 情态动词 属于助动词。英语的助动词(auxiliary) 主要有两类：基本助动词(primary auxiliary) 和情态助动词 (modal auxiliary)。基本助动词有三个：do, have 和 be；情态助动词有十三个： may, might; can, could; will, would; shall, should; must, need, dare, used to, ought to. 上述两类助动词的共同特征是，在协助主动词构成限定动词词组时，具有作用词的功能：（ 1） 构成否定式：He didnt go and
2、 neither did she. The meeting might not start until 5 oclock. （ 2） 构成疑问式或附加疑问式：Must you leave right now? You have been learning French for 5 years, havent you? （ 3） 构成修辞倒装：Nowhere can he obtain any information about his sister. Hardly had he arrived when she started complaining. （ 4） 代替限定动词词组：A: Who
3、 can solve this crossword puzzle? B: Tom can. A: Shall I write to him? B: Yes, do. 情态动词 是一种本身有一定的词义, 但只能与其他原形动词一起构成句子的谓语，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；或表示说话人的情绪,态度或语气。如：We can be there on time tomorrow. 我们明天能按时去那儿。May I have your name? 我能知道你的名字吗？Shall we begin now? 我们现在就开始吗？You must
4、obey the school rules. 你必须遵守校规。情态动词有四类：只做情态动词：must, can (could), may (might), ought to，可做情态动词又可做实义动词：need, dare 可做情态动词又可做构成时态的助动词：shall (should), will (would) 具有情态动词特征：have(had) to, used to，be able to 情态动词无人称和数的变化，数量不多, 但用途广泛。英语情态动词can, could, may, might, will, would, shall, should, ought to, dare,
5、need，must 以及半情态动词have to.，be able to，used to 主要用来表示请求，许可 , 可能，推测，义务，职责，意图，打算，意愿，意志，决心，能力，规劝，责备，必然等含义。2 二. 情态动词的位置 : 情态动词在句中放在谓语动词之前，谓语动词前若有构成时态、语态的助动词， 则情态动词放在助动词之前。疑问句中，情态动词则移到主语之前。如I can see you. Come here. 我能看见你，过来吧。He must have been away. 他一定走了。What can I do for you? 你要什么？How dare you treat us l
6、ike that！ 你怎能那样对待我们！三. 情态动词的特点 : 情态动词无人称和数的变化，情态动词后面跟的动词需用原形。其否定式是在情态动词后面加“not“ 构成。个别情态动词有现在式和过去式两种形式，如情态动词dare 的过去式为 dared 。一般来说，情态动词的过去式是用来表达更加客气、委婉的语气，故时态性不强，可用于过，现在或将来。如：He could be here soon. 他很快就来。（用于现在时态，表不确定的猜测）We cant carry the heavy box. 我们搬不动那箱子。（用于现在时态，表能力）Im sorry I cant help you. 对不起，我
7、帮不上你。（用于现在时态，表不允诺）四. 情态动词的用法 : (一) can 和 could （be able to ）1. can (could) 两种时态能用来表示” 现在和过去的能力” ，但若要表述“具体已经做成功某件事” ， 则要用 was / were able to do sth.的形式 ,相当于 succeeded in doing / managed to do sth.。如：He can speak French. With our help, he was able to build the house. 2. 用于口语体，表示请求或许可。现在时态中could 比 can
8、更加委婉。-Can I go now? -Yes, you can. - Could I help you? -Yes, please. 3. 表示推测的可能性，常用于否定句和疑问句。- Can he be at school now? -Today is Sunday. He cant be at school.- There is no light in the room. Can she have gone to bed? - She can t have gone to school- it s Sunday.4. 若表述由客观事物的性质决定其有可能性，在肯定句中也可用can。Wool
9、en sweaters can shrink when washed in hot water. Anybody can make mistakes. Could have done 可用在肯定句中表示过去存在的可能性* may have done She could have gone out with some friends yesterday. 5. Could have done 可以用来表示虚拟语气，假设某事原本有可能发生（却没有发生）。3 It was silly to throw the TV out of the window. It could have hit someb
10、ody. You are late again. You could have got up earlier. （二） may 和 might 1 表示请求和允许，属于正式用法。而can 和 could 用于请求和允许则口语化。May I watch TV now? Yes, you may. （No，you mustn t.）2 表示可能性 ; 猜测时用might 比 may 表述更加不确定may/might have done 用来表示对过去的揣测He may be busy these days. She might come here tomorrow. I m not sure.Th
11、e box might / may have been opened by someone. may not 可能不；不可能；一定不可He may not accept your invitation. 3 表示祝愿Wish you success! May you succeed! May you all be happy! （三） must 和 have to 1 表示必须，一定要，有时可以用have to 代替must 只用于现在和将来的“必须”， 表达的是是主观的看法，是出于社会责任、道德、义务、礼仪、习俗而必须做某事have to 则有多种时态（had to，shall/will h
12、ave to, should/ would have to）, 而且强调 客观情况使人只得做某事As students, we must work hard. I really must stop smoking now. I had to leave early because I wasn t feeling well.-Must I come here? - Yes, you must. No, you needn t. needn t / don t have tomust not mustnt若用在反义疑问句中，尾巴用mustn t 或 needn t 来呼应。We must wor
13、k hard, mustn t we?They must come here again tomorrow, needn t they?2. 其否定表达mustn t 表示禁止“不准” ， “不可以”；而needn t ，don t have to 则表示“不必”We mustn t make great noise in class. If you don t like the soup, you needn t / don t have to eat it. 3. 表示非常肯定的推测，意思是“ 一定是 ” “ 准会 ”It must be raining outside. She must
14、 be reading in the dorm now. must have been/ had/ done 用来表述对讲话以前所发生过事的推测， 若在反义疑问句中， 由于 must 表述很肯定的猜测，可以把它看作事实，尾巴用She must have been in the lab yesterday afternoon, wasn t she? It must have rained last night, didn t it?4 He must have gone over the article, hasn t he?They must have learnt it before, h
15、aven t they? 表猜测时， must be 的反义表达为can t be “不可能是”-He must be a layer. -He can t be a layer. He is my neighbor, an actor. 4. 表述对意外发生情况的惊讶、不耐烦，意为“偏偏”He must fall ill just before the terminal exam. (四) need 和 dare （过去式dared）need 和 dare 都可以用作情态动词和实意动词。在肯定句中，它们常用作实意动词，在否定句、疑问句和if 条件句中，它们才常用作情态动词。1. need /
16、dare 在肯定句中，用作实意动词She needs to do it. No one dares to do it. 2. 用在否定句 , 疑问句和if 条件句中，用作情态动词。若仍然用作实意动词，则要加用助动词。He need not do that. （ He doesn t need to do it. ）I dare not do it. （ I don t dare (to) do it.）Need you borrow so much money? (Do you need to borrow so much money?) Dare Tom cheat on tests again? (Does Tom dare to cheat on tests again?) If anyone need loan money from the bank, I ll lend a hand. (I
