情態(tài)動詞用法歸納

1、情態(tài)動詞有 can （could）, may （might）, must, have to, shall （should, will （would）,dare （dared）, n eed （n eeded）, ought to等。情態(tài)動詞無人稱和數(shù)的變化；不能單獨使用，必須與其后的動詞原形構(gòu)成謂語。一、can, could1）表示能力（體力、知識、技能）。Can you lift this heavy box?（體力）Mary can speak three Ian guages.（知識）Can you skate? （技能）此時可用be able to 代替。Can只有一般現(xiàn)在時和一般過去

2、式；而 be able to 則有更 多的時態(tài)。I ll not be able to come this after noon.當(dāng)表示經(jīng)過努力才得以做成功某事”時應(yīng)用 be able to，不能用Can。如：He was able to go to the party yesterday eve ning in spite of the heavy rain.2）表示請求和允許。Can I go now?Yes, you can. / No, you can t.此時可與may互換。在疑問句中還可用 could,might 代替，不是過去式，只是語氣更委 婉，不能用于肯定句和答語中。Coul

3、d I come to see you tomorrow?Yes, you can. （ No, I m afraid not.）3）表示客觀可能性（客觀原因形成的能力）。They ve cha nged the timetable, so we can go by bus in stead.This hall can hold 500 people at least.4）表示推測（驚訝、懷疑、不相信的態(tài)度），用于疑問句、否定句和感嘆句中。Can this be true?This can t be done by him.How can this be true?二、may, might1）

4、表示請求和允許。might比may語氣更委婉，而不是過去式。否定回答時可用cant或must nt，表示不可以，禁止”。-Might/ May I smoke in this room?No, you mustn t.- May/Might I take this book out of the room?Yes, you can. （No, you can t / mustn t.）用May I. ?征徇對方許可時比較正式和客氣，而用Can I. ?在口語中更常見。2）用于祈使句，表示祝愿。May you succeed!3）表示推測、可能性（不用于疑問句）。might不是過去式，它所表示的

5、可能性比may小。1. He may /might be very busy now.2. Your mother may /might not know the truth.三、must, have to1）表示必須、必要。You must come in time.在回答引出的問句時，如果是否定的，不能用 mustn t （禁止，不準(zhǔn)），而用neednt, don t have to （不必）Must we hand in our exercise books today?Yes, you must.No, you don t have to / you needn t.2）must是說話

6、人的主觀看法，而have to則強(qiáng)調(diào)客觀需要。Must只有一般現(xiàn)在時，haveto有更多的時態(tài)形式。1. he play isn t interesting, I really must go now.2. I had to work whe n I was your age.3）表示推測、可能性（只用于肯定的陳述句）1. You re Tom s good friend, so you must know what he likes best.2. Your mother must be wait ing for you now.四、dare, n eed1）dare作情態(tài)動詞用時，常用于疑

7、問句、否定句和條件從句中，過去式形式為dared。1. How dare you say I m unfair?2. He daren t speak English before such a crowd, dare he?3. If we dared not go there that day, we couldn t get the beautiful flowers.2）need作情態(tài)動詞用時，常用于疑問句、否定句。在肯定句中一般用must, have to,ought to, should 代替。1. You needn t come so early.2. - Need I fin

8、ish the work today?Yes, you must. / No, you needn t.3）dare和need作實義動詞用時，有人稱、時態(tài)和數(shù)的變化。在肯定句中，dare后面常接帶to的不定式。在疑問句和否定句中，dare后面可接帶to或不帶to的不定式。而need后面只能接帶to的不定式。1. I dare to swim across this river.2. He doesn t dare （to） answer.3. He n eeds to finish his homework today.五、shall, should1）shall用于第一人稱，征求對方的意見。

9、What shall we do this eve ning?2）shall 用于第二、三人稱，表示說話人給對方的命令、警告、允諾或威脅。1. You shall fail if you don t work hard.（ 警告）2. He shall have the book whe n I fin ish it.（允諾）3. He shall be puni shed.（威脅）六、will, would1）表示請求、建議等，would更委婉。Will / Would you pass me the ball, please?2）表示意志、愿望和決心。1. I will n ever do

10、 that aga in.2. They asked him if he would go abroad.3）would表示過去反復(fù)發(fā)生的動作或某種傾向。would表示過去習(xí)慣時比 used to正式,且沒有“現(xiàn)已無此習(xí)慣”的含義。1. During the vacation, he would visit me every other day.2. The wound would not heal.4）表示估計和猜想。It would be about ten o clock when she left home.七、should, ought to1）should, ought to表示“

11、應(yīng)該”，ought to 表示義務(wù)或責(zé)任，比 should語氣重。1. I should help her because she is in trouble.2. You ought to take care of the baby.2）表示勸告、建議和命令。 should, ought to可通用，但在疑問句中常用should 。1. You should / ought to go to class right away.2. Should I open the win dow?3）表示推測should , ought to （ 客觀推測）,must（ 主觀推測）。1. He must

12、be home by now.（ 斷定他已到家）2. He ought to/should be home by now.（不太肯定）3. This is where the oil must be.（直爽）4. This is where the oil ought to/should be.（含蓄）八、情態(tài)動詞+不定式完成式（have done）1）can / could + have done在肯定句中表示“本來可以做而實際上能做某事，是虛擬語氣；在疑問句或否定句中表示對過去行為的懷疑或不肯定，表示推測。1. You could have done better, but you did

13、n t try your best.（虛擬語氣）2. He can t have been to that town.（推測）3. Can he have got the book?（推測）2）may / might + 不定式完成式（ have done）表示對過去行為的推測。不能用于疑問句中，沒有虛擬語氣的用法。Might所表示的可能性比may小。1. He may not have fini shed the work .2. If we had taken the other road, we might have arrived earlier.3) must +不定式完成式(hav

14、e done)用于肯定句中，表示對過去行為的推測。意為“一定、想必”。其疑問、否定形式用can， can t 代替。參看 1) can / could + have done表示推測。1. You must have see n the film Tita nic.2. He must have bee n to Shan ghai.4) should + 不定式完成式(have done)用于肯定句中，表示對過去行為的推測。He should have fini shed the work by now。表示“本應(yīng)該做而實際上沒有做某事”，其否定式表示某種行為本不該發(fā)生卻發(fā)生了?？梢耘cought to + 不定式完成式(have done )互換。1. You ought to / should have helped him. (but you didn t.)2. She should n t have take n away my measur