7情态动词

1 情态动词 （讲解部分由严洁、朱星整理；综合练习题部分由周丽丽整理） 一，情态动词的特征。 1， 情态动词不能单独作谓语，必须和行为动词或系动词连用，构成谓语。 She must be a teacher. I can speak English. 2， 情态动词无人称和数的变化（have to除外）。 I can speak English. She can speak Chinese. 3， 情态动词后接动词原形。 She may lose her way. 4， 情态动词具有助动词的作用，可用来构成否定句、疑问句。 Can you sing an English song? I can’t sing an English song.

二，情态动词的用法。 1， can / could的用法。 (1) 表示能力，意为“能，会”。 Can you play basketball? (2) 表示怀疑、猜测，常用于否定句和疑问句中。如： She can’t be a teacher. Tom can’t be in the classroom. (3) 表示请求或允许。意为“可以”，相当于may。如： Can I go now? You can leave now. 注意：表示“请求”时，could的语气比can更委婉。（此时，could不是can的过去式。） (4) 以can或could开头的一般疑问句，其肯定或否定回答分别用can / could和can’t / couldn’t。如： —Could you skate last year? —Yes, I could / No, I couldn’t. 2， may / might的用法。 (1) 表推测，意为“可能，也许”。如： He may come tomorrow. The story may not be true. （2）表请求，许可，意为“可以”。如： May /Might I come in? May I borrow your book? 注意：may / might 表示请求时，且主语为第一人称的一般疑问句时，其否定回答用mustn’t，不用may not,意为“不可以；不许；禁止”。如： —May I go now? —No, you mustn’t. (3) 表示祝愿。——此时不用might。如： 2

May you success！祝你成功！ 3，must / have to的用法。 （1）表示“必须，应该” Must：表示说话人的主观愿望，只有现在时，意为“必须”

have to：则表示客观需要，能用于更多时态（过去时或将来时），意为“不得不，只好”；否定式： mustn’t表示“不准，禁止”

don’t have to表示“没必要”。 You mustn’t smoke in classroom As he had broken his leg, he had to stay in bed. 注意：must 开头的问句，肯定回答用must；否定回答用needn’t或don’t have to，不能用mustn’t。 —Must I finish the work today? —No, you needn’t (2) must可以表推测。一般用于肯定句中。 There is someone knocking at the door. It must be Jim.

4，shall / should的用法。 (1) Shall: 表示征求意见，询问。一般用于第一人称或第三人称。如： Shall I open the window? What shall we do now? (2) should: 表式劝告，建议或命令。 We should obey traffic laws. You should study hard. 5，will / would 的用法。 (1) will: 用于第二人称表示询问、请求。 Will you come to my birthday party. Will you pass me the book. (2) will: 表示“意愿，允诺”。 We will do anything for you. (3) would: 表示请求，建议。比will语气更委婉。 Would you tell me the way to the station. 6，used to的用法。 Used to: “过去常常”，但现在不这样了。 I used to go to school by bike, but I don’t ride anymore. 7，need / dare的用法。 （1）need：“需要，必须”，用于否定句或疑问句中。 You needn’t come to school so early. Need I do the housework? （2）dare：“敢”，常用于否定句或疑问句中。dare有过去式dared。 Daren’t you read what the notice says? 3

She dare not do it. need / dare用作实义动词，多用于肯定句中。构成疑问句或否定句时，应借助于助动词do, does, did,其后必须接待to的不定式。

need / dare用作情态动词，多用于否定句或疑问句中，否定时，可在其后直接加not, 变一般疑问句时，把need或dare直接提前。

8，ought to的用法。 Ought to: “应该，应当”,表示义务或责任。比should语气更强。其否定为“ought not to”. Humans ought to stop polluting nature. Such things ought not to be allowed to happen again. 9，had better的用法。 Had better：“最好是…” “Had better + 动词原形”：表示最好做某事，其否定为“had better not do sth”。 You’d better stay at home. You’d better try it again if you fail this time. 10，情态动词表推测： 情态动词表推测的可能性由弱到强的排列顺序如下： Might→may→could→can→should→ought to→would→will→must. 时 态 肯定推测 否定推测 疑问推测

对现在的推测

Must/may/can+be…… Can’t be….. Can sb be……

对过去的推测

Must/can/may/might/could+have done Must/can/may/might/could+not+have done Can/could sb have done

对将来的推测

Must/can/may/could/might+do Can’t/may not +do Can/ may+do 4

一、“情态动词+动词原形” 表示对现在的推测。 1，can表示推测时一般用于否定句或疑问句。如： That man can’t be her husband, she is still single. —Who is knocking at the door? —Can it be the postman? 2，must表示肯定的推测，一般用于肯定句中。如： He must be in his office now. Mr. Li must be working now, for the lights in his office are still on. 3，might 表示推测时不一定是may的过去时，只是表示其可能性较小。如： The man may be the headmaster. —Where is Mr. Li? —might be working in his office. —May Mr. come? —He might not come here. 4，would 表示推测时 也不一定是will 的过去时，只是说话者的语气要委婉一些，说话留有余地.如: We will go to the cinema this afternoon. He would come here if the weather were fine. 5，should（有时用ought to）表示推测的可能性比较大，仅比must的可能性小一点。如： It is already 10 o＇clock now, they should be there. Your clothes ought to be ready by 12 tomorrow. 6，could表推测时，语气比can要弱。如： ------Could it be an animal? ------It could not be，because it is not moving.

二、情态动词表示对过去可能发生事情的推测。 1，“must +have done/been——表示对已经发生的事情的推测，意为“一定，想必”，一般只用于肯定句中，其否定形式是“can’t /couldn’t have done”，表示“不可能，肯定不会”。 She must have seen the film before. You must have been to Shanghai. They can’t have gone out, because the light is on.

2，“ought to /should +have done /been”——表示“本应当做某事，而实际上并没有做”； “oughtn’t to/ shouldn’t+完成式”——“本来不应当做，而实际上却做了”。以上结构常带有说话者的责备的感情色彩。如： You should have finished your homework earlier (but in fact you did not finish it on time). You shouldn’t /oughtn’t to have gone to bed when you woke up at five (but in fact you went to bed again then).

3，“would（很少用will）+have done /been”——表示“过去很可能发生了某事或存在过某种状态”。如： —Where is Mr. Wang? I can’t find him in his office.