英语语法：助动词、情态动词

英语语法：助动词、情态动词

五．助动词和情态动词

A．助动词：没有独立的词义，不能单独构成谓语，往往有形式变化：be (am, is, are, was, were, being, been), have (has, had, having), do (does, did), shall, will (should, would).

1．构成一般现在时与一般过去时以外的各种时态；2．构成被动语态；3．构成否定句和疑问句；4．加强语气；5．替代，以避免重复；6。构成虚拟语气。

5) I th ought she’d come, but she didn’t (=didn’t come).

B．情态动词：有一定的词义，没有人称和数的变化，不能单独构成谓语，后接动词原形：can, could, may, might, will, shall, would, should, must, need, ought to, dare等。

1．can/ could：1）表能力；2）许可；3）可能性；4）推测（通常用于否定句或疑问句）

1) She can drive, but she can’t ride a bike. My son could (=was able to) read and write when he was four. 但：He was able to pass his examination as a result of his hard study. (设法或成功做了某事)

2) Students can’t smoke in t he classroom. I could borrow my father’s car whenever I liked.

3) Even experienced teachers can make mistakes. (理论上的可能性)

Our club finances may be improved. It could be better to stay here. (实际上的可能性)

4) The story can’t be true. (现在或未来情况) He couldn’t have said such a thing. (过去情况) 2．may/ might：1）可能性、推测；2）许可(否定：may not, m ustn’t)；3）委婉的责备、不满；4）目的、让步状语从句；5）固定搭配：may (might) as well, may well；6）表祝愿（倒装）

1) They might have known the matter earlier. (过去的推测)

I think it might rain. It may snow tomorrow. He may be having the meeting now. (现在或未来的推测)

2) You may use my dictionary. My boss told me I might have

a vacation.

3) You might have told the truth. （对照虚拟语气中的类似句式）

4) They moved over a little so that I might sit down. Whatever he might say, no one believed him,.

6) May you have merry Christmas!

3．must：1）义务（否定：need n’t）；2）不允许（否定句中）；3）推测

1) — Must I wash the dishes at once? — Yes, you must. / No, you needn’t.

2) You must not speak ill of others.

3) It must rain soon. He must be having the meeting now. (对现在或未来进行“肯定”猜测)

No one answered the phone bell. They must have gone out. （对过去已发生的情况进行“肯定”猜测）4．need：1）需要；2）needn’t have + 过去分词（过去做了不必要做的事情）；3）实义动词

1) You needn’t work so hard.You need not meet him unless you’d like to.

2) You needn’t have bought the dress. 3) You don’t nee d to come if you feel sick.

5。dare：1）敢；2）实义动词

1) Mary dare not touch the snake. 2) I have never dared to tell him about it.

6．will/ would：1）时态的区别；2）语气的区别

1) I will marry you whatever happens. His father was angry

because he wouldn’t obey him.

2) Will you pass me the salt, please? Would you like to come and join us at the party?

7．shall/ should/ ought to：1）第一、三人称疑问句，表示征求同意；2）第二、三人才陈述句，表示义务、命令，许诺；3）should/ ought to +动词原形：义务；4）should/ ought to +现在完成式，表责备、后悔（该做而没做的事）

1) Shall I fetch a doctor for you? Shall he come at once?

2) You shall do as you see me do. They shall never interfere in my private affairs again.

3) You don’t look well. You ought to go to see the doctor. You should apologize to him.

4) He shouldn’t have said such a thing. You ought to have worked harde r.

8．would (会), should (应该), might (可能), ought to (应该) 用于虚拟语气（参见“虚拟语气”部分）

1. Not until the game had begun ________ at the sports ground. (2000.6)

A. had he arrived

B. did he arrive

C. would he have arrived

D. should he have arrived

2. Investigators agreed that passengers on the airliner _______ at the very moment of the crash. (2002.6)

A. should have died

B. must have died

C. must be dying

D. ought to die

3. The careless man received a ticket for speeding. He _______ have driven so fast. (2002.12)