（一）助動詞有be, have, do, will, shall。它們本身沒有詞義，只和實義動詞的一定形式構成復合謂語，用來表示時態和語態，構成否定、疑問及加強語氣等。
1、be (am, is, are, were, been)
(l)“be + -ing”構成進行時態；（2）“be + 過去分詞”構成被動語態；（3）“be + 動詞不定式”構成復合謂語：①表示按計劃安排要發生的事。The prime minister is to visit Japan next year. 總理將于明年訪問日本。② 用于命令。You're to do your homework before you watch TV.你得做完了作業才能看電視。
2、have (has, had)
(1)“have+過去分詞”構成完成時態。如：Have you seen the film ? (2)“have been + -ing”構成完成進行時態。如：What have you been doing these days? 這些日子你一直在干什么?
3、do (does, did)
(1)“do not + 動詞原形”構成行為動詞的否定式。如：His brother doesn’t like playing basket.；(2)“Do + 主語 + 動詞原形”構成行為動詞的一般疑問句。Does he go to school by bike every day? (3)“do + 動詞原形”用于祈使句或陳述句中表示加強語氣。如：I did go to see him, but he wasn’t in我確實去看望他了，但他不在家。Do do some work. 請一定做點什么；(4)代替前面剛出現的動詞以避免重復。My mother told me to go to bed early. So I did.
4.will, shall (would, should)
“will (shall+動詞原形”構成一般將來時，一般來說shall用于第一人稱，will用于第二人稱或第三人稱，口語中常用will代替shll，如：We will have a meeting to discuss the problem.
（二）情態動詞
情態動詞表示說話人對某一動作或狀態的態度，可以表示“可能”、“可以”、“需要”、“必須”或“應當”等之意。情態動詞沒有人稱和數的變化。但不能單獨作謂語動詞用，必須和不帶to的不定式連用構成謂語動詞。只有情態動詞ought要和帶to的動詞不定式連用，在句中作謂語用。
將情態動詞置于主語之前即構成其疑問式，在情態動詞之后加not既構成其否定式。現將各情態動詞的基本用法分述如下：
1、can和could (could為can的過去式) 的基本用法
(1)表示能力，如：He can speak English better than you. (2)在疑問句和否定句中表示“懷疑”、“猜測”或“可能性”，如：Can this green bike be Liu Dong's? (3)表示“許可”時can可以和may換用，如：You can (may) go home now. (4)如果要表示語氣婉轉，可用could代替can，這時could不再是can的過去式，如：Could you come again tomorrow? (5)can和be able to都可表示能力，兩者在意思上沒有什么區別。但是can只能有現在式和過去式，而be able to則有更多的形式，如：He will be able to do the work better.
2、may和might (might為may的過去式)的基本用法
(1)表示允許或征詢對方許可，有“可以”之意，如：You may use my dictionary. 在回答對方說“可以做某事”或“不可以做某事”時，一般多不用may或 may not，以避免語氣生硬或不容氣。而用比較婉轉的說法進行回答。如：---- May I use this dictionary? ---- Yes, please. 或 ---- Certainly. 在請求對方許可時，如果Might I…? 就比用May I…? 語氣更婉轉些，如：May I have a look at your new computer? 但是表示“阻止”或“禁止”對方做某事時，要用must not代替may not，如：---- May we swim in this lake? ---- No, you mustn’t. It’s too dangerous. (2)may或 might都可以表示可能性，表示“或許”、“可能”之意，如果用might表示可能性，則語氣更加不肯定，如：They may (might) be in the library now .
3、must的基本用法
(1)must表示“必須”、“應該”之意，其否定式 must not，縮寫形式為 mustn't，表示“不應該”，“不準”、“不許可”或“禁止”之意，如：We must study hard and make progress every day. You mustn't touch the fire. (2)對以must提出的疑問句，如作否定回答時，要用needn't或用don't (doesn't) have to (不 必)來回答，而不用mustn't，因為mustn't表示的是“禁止”或“不許可”之意，如：---- Must we finish the work tomorrow? ---- No, you needn't (don't have to), but you must finish it in three days. (3)在肯定句中must可以表示推測，表示“一定”或“必定”之意，如：---- Whose new bike can it be? ---- It must be Liu Dong's. I know his father has just bought him a new one.
4、can, could, may, must后接完成式的用法
(1)can, could后接完成式的用法：①在否定句或疑問句中表示對過去發生過的事情的“懷疑”或“不肯定”的態度，Could he have said so? ②在肯定句中，可以表示過去可能做到而實際并沒做到的事情，有“勸告”或“責備”的語氣。如：---- When did you answer her letter? ---- Only yesterday. ---- It's too late. You could have answered it earlier, I am sure. (2)may, might后接完成式的用法 ①表示對過去某事的推測，認為某一件事情在過去可能發生了。如果使用might，語氣就比較婉轉或更加不肯定，如：Mary might have learned some Chinese before. ②可以表示過去本來可以做到而實 際沒有做到的事情，有“勸告”或“責備”的語氣，如：You didn't do the work well that day. You might have done it better. (3)must后接完成式的用法：表示對過去某事的推測，認為某事在過去一定做到 了，如：Liu Dong isn’t in the classroom. He must have gone to the library.
5、have to 的基本用法：have to和must的意義相近，只是 must側重表示說話人的主觀看法，而have to 則表示客觀需要，如：I must study hard. I had to give it up because of illness.
6、ought to的基本用法
(l)表示根據某種義務或必要“應當”做某事，語氣比should強，例如：Everyone ought to obey the traffic regulations. (2)表示推測，注意與must表示推測時的區別：He must be home by now .(斷定他已到家)，He ought to be home by now .(不十分肯定)，This is where the oil must be.(比較直率) ，This is where the oil ought to be. (比較含蓄) ；(3)“ought + have+ 過去分詞”表示過去應做某事而 實際未做。例如：You ought to have helped him. (but you didn’t) 這時，ought與 should可以互相換用。注意，在美國英語中ought to 用于否定和疑問句時to可以省略。例如：Ought you smoke so much? You oughtn’t smoke so much.
7、dare的基本用法
(l)dare (dared為其過去式) 作情態動詞用時，主要用于否定句，疑問句和條件從句中，如：Dared he bread the traffic regulations again? (2)在現代英語中dare常用作行為動詞，其變化與一般行為動詞相同，如：She dares to stay at home alone at night.
8、need的基本用法
(1)need作情態動詞用時，主要用于否定句和疑問句中，如：He needn't worry about us now. (2)need也可作為行為動詞用，可用于肯定句，否定句和疑問句中，其后可接名詞、代詞、動名詞或帶 to 的動詞不定式為其賓語。如：You need to practise reading aloud every day. (3)needn't后接完成式可以表示過去做了一件本來不必要做的事情，如：---- Did you answer the letter yesterday? ---- Yes, I did. ---- But you needn’t have answered it.
9、shall的基本用法
(1)shall用作情態動詞時，用于第二、三人稱，表示說活人的意愿，可表示“命令”、“警告”、“強制”、“威脅”或“允諾”等意，如：He shall go first, whether he wants to or not. (2)在疑問句中，shall用于第一、三人稱，表示說話人的征詢對方意見或請求指示，如：Shall I open the door?
10、should的基本用法
(1)should作為情態動詞可以表示“建議”或“勸告”，有“應該”之意，如：You should learn from each other. (2)should后接完成式表示過去沒有做到本來應該做的事情，或是做了本來不應該做的事情。如：You should have give him more help.
11、will的基本用法
(1)用于各人稱，可以表示“意志”或“決心”，如：I have told him again and again to stop smoking, but he will not listen. (2)在疑問句中用于第二人稱，表示說話人向對方提出請求或詢問對方的意愿，如：Will you please tell me how to get to the Capital Gymnasium? (3)will可以表示一種習慣性的動作，有“總是”或“會要”之意，如：Every morning he will have a walk along this river.
12、would的基本用法
(1)would作為will的過去式，可用于各人稱，表示過去時間的“意志”或“決心”，如：He promised he would never smoke again. (2)在疑問句中，用于第二人稱，表示說話人向對方提出請求或許問對方的意愿時，比用will的氣更加婉轉，如：Would you like some more coffee? (3)在日常生活中，學用“I would like to…”表示“我想要”或“我愿意”之意，以使語氣婉轉，如：I would like to do Ex.2 first. (4)would可以表示過去的習慣動作，比used to正式，并沒有“現已無此習慣”的含義。如：Last year our English teacher would sometimes tell us stories in English after class. / During the vacation he would visit me every week. (5)表料想或猜想，如：It would be about ten when he left home./ What would she be doing there?/ I thought he would have told you about it.
13、used to, had better, would rather的用法
(1)used to表示過去的習慣動作或狀態，現在已不存在，在間接引語中，其形式可不變，例如：He told us he used to play foot ball when he was young. 在疑問句、否定句、否定疑問句或強調句中，可有兩種形式。疑問句：Did you use to/ Used you to go to the same school as your brother? 否定句：I usedn’t to / didn’t use to go there. (usedn’t 也可寫作usen’t)；否定疑問句：Usen’t you to/ Didn’t you use to be interested in the theatre? 強調句：I certainly used to/ did use to smoke, but it was a long time ago.；其反意疑問句或簡略回答中，也有兩種形式：She used to be very fat. didn’t she?/ use(d)n’t she? Did you use to play chess? Yes, I did./ Used you to get up early in the morning? Yes, I did./ used to. (2)had better意為“最好”，后接不帶to的不定式，例如：---- We had better go now . ---- Yes, we had (we'd better/ we had better)./ Hadn’t we better stop now? (Had we better not stop now?)/ I think I’d better be going. (用于進行時態，表“最好立即”)/ You had better have done that (用于完成時態，表未完成動作) 注：had better用于同輩或小輩，對長輩不可用。(3)would rather意為“寧愿”，表選擇，后接不帶to的不定式，例如：I’d rather not say anything./ Would you rather work on a farm?/ ---- Wouldn’t you rather stay here? ---- No, I would not. I’d rather go there. 由于would rather表選擇，因 而后可接than，例如：I would rather work on a farm than in a factory. / I would rather watch TV than go to see the film/ I would rather lose a dozen cherry trees than that you should tell me one lie./ I’d rather you didn’t talk about this to anyone. (句中的 'd rather不是情態動詞，would 在此是表愿望的實義動詞)
練習、助動詞與情態動詞
1. If they _________ to do this work, he might do it some other way.
A. were B. should C. will D. can
2. I was told yesterday that the company _________ me to Rome next week for a business conference.
A. should have sent B. were going to send C. should be sending D. should send
3. Let's take a walk, ________? A. will we B. don't we C. do we D. shall we
4. He was a good swimmer so he _________ swim to the river bank when the boat sank.
A. could B. might C. should D. was able to
5. I went to the doctor's yesterday, I had to wait for half an hour before he ________ see me.
A. can B. may C. might D. could
6. ---- _________ this book be yours? ---- No, it ________ not be mine. It ________ be his.
A. Can, must, may B. May, might, must C. Can, may, must D. Must, can, may
7. "We didn't see him at the lecture yesterday. " "He _________ it. "
A. mustn't attend B. can't have attended C. would have not attended D. needed have attended
8. They _________ the plane, or perhaps they have been prevented from coming for some reason.
A. can have missed B. may have missed C. can have lost D. may have lost
9. Since the ground is white, it _________ last night.
A. had snowed B. must have snowed C. must be snowing D. must have been snowing
10. You must be fifty, ________?
A. mustn't you B. needn't you C. aren't you D. mnyn't you
11. You must have seen him off yesterday, _________?
A. haven't you B. didn't you C. mustn't you D. needn't you
12. ---- That must be a mistake. ---- No .it _________ be.
A. can't B. isn't able to C. can D. was able to
13. He had known the matter before you told him, so you _________ have told it to him.
A. mustn't B. can't C. needn't D. shouldn't
14. How ________ so?
A. dare you to say B. dare you say C. do you dare say D. dare to say
15. You are their teacher. You _________ care of them.
A. should to take B. might to take C. ought to take D. need to take
16. She is studying medical science now but she _________ a lawyer.
A. used to be B. would be C. were D. had been
17. If you were in an English-speaking country, you, too, _________ English every day.
A. will be used to speak B. will be used to speaking
C. must be used to speak D. would be used to speaking
18. I did not call to make my airline reservation (預訂) but I _________.
A. should have B, may have C. must have D. shall have
19. As a girl, she _________ get up at six every day.
A. would B. will C. might D. should
20. Don't you remember that we _________ to the cinema tonight?
A. would go B. go C. are going D. will be gone
21. ---- Shall I tell John about it? ---- No, you _________. I've told him already.
A. needn't B. wouldn't C. mustn't D. shouldn't
22. "Would you mind if I open the window?" “__________”.
A. I don't like it B. Yes .please C. No, please D. No. I'm sorry
23. "Would you tell me something about the affair?" “__________”.
A. Yes .please B. All right C. Not at all D. I do
24. M:________?
T:I'd love to, but I'm afraid I have no time."
M:0h, no. You'll surely come over.
T: It's very nice of you. But I'm sorry I have to go to a meeting.
A. Do you have lunch out in a restaurant B. Shall I have you with me at my birthday
C. Did you go to see the film D. Have you enjoyed yourself at the party
25. "You ought to have come here ten minutes ago?" "Yes, I _________. "
A. ought to B. ought to have C. ought D. have ought to
26. "Would you like to go out for a walk?" "Yes, ___________. "
A. I'd like to B. I'd like C. I'll like to D. I would
27. ________ you succeed !
A. Can B. May C. Must D. Will
28. Did he need ________ then?
A. leave B. to leave C. leaving D. left
29. Do you think if he dares _________ in public.
A. speak B. speaking C. to speak D. spoken
30. He ________ eating American food since he came here.
A. used to B. has been used C. has been used to D. was used to
31. A computer ________ think for itself; it ________ be told what to do.
A. may not, must B. mustn't, might C. shouldn't, could D. can't, must
32. "________ you mind my opening the window?" "Not at all. "
A. Shall B. Should C. Will D. Would
33.1 didn't hear the phone. I _________ asleep.
A. must be B. must have been C. should have been D. could have been
34. You _________ me about it earlier, but you didn't.
A. should have told B. would have told C. must have told D. should tell
35. The teacher told the students that they ________ keep silent in class all the time.
A. ought to not B. ought not to C. ought not to have D. can't
36. "May I go now?" "No, you ________. "
A. mustn't B. needn't C. mightn't D. won't
37. You _________ do the exercise if you don't want to.
A. may not B. can't C. mustn't D. needn't
38. You _________ pay more attention to your spelling next time.
A. would B. should C. will D. shall
39. The girl _________ out alone at night.
A. dare not go B. dare not to go C. dares not go D. does not dare go
40. There ________ be a lot of small houses on both sides of the street.
A. used to B. get used to C. would D. did use to