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(三) 情态动词
所谓情态动词是指它含有一定的含意，可以表达某种感情和说话的口气，但是它不可以单独使用作谓语动词。学习情态动词主要要学习英语国家的语言习惯和表达法，特别是在口语中不要过分追求原理，更不要不根据说话场合而进行推理，编造出一些语法结构正确的中文式英语。学习时可参考表８－４。
表8－4情态动词用法
| 情态动词 |
功用 |
例句 |
|
cancould |
表示能力 |
The young boy can speak English. |
|
表示可能性 |
Anyone can make mistakes. |
|
表示怀疑或推测(限于否定句，疑问句或感叹句中) |
He can't be late.
Canhe be an honest man? |
|
表示允许 |
Can I watch TV now? |
|
could 用于现在时代替can 使语气更委婉 |
Could you please do me a favour? |
| maymight |
表示允许 |
May I come in? |
|
表示推测(用于肯定句) |
You may be right. |
|
表示请求或规劝 |
You might pay more attention to me. |
|
表示祝愿 |
May you be happy! |
|
must |
表示义务或责任 |
We must obey the rules. |
|
表示很有把握的推测(用于肯定句) |
She looks pain. She must be ill.
They must have been/gone home. |
|
否定式表示禁止 |
You mustn't smoke in the public. |
|
ought to |
表示义务 |
We ought to look after old people. |
|
表示推测 |
There ought to be no trouble. |
|
shall |
表示允许或命令(用于第二、第三人称) |
You shall leave after class.
He shall be sent for. |
|
表示征求意见(用于第一、第三人称的疑问句中) |
Shall I take it away?
Shall we begin now? |
|
should |
表示义务或建议 |
We should learn some English. |
|
表示推测或可能 |
They should finish it by now. |
|
表示惊奇、赞叹、愤怒等感情，常与why连用 |
Why shouldn't you be calm?
Why should I be nervous? |
|
用于虚拟语气 |
You should have been here earlier. |
|
will |
表示意志或决心 |
I will do it myself. |
|
表示有礼貌的请求 |
Will you please go this way? |
|
表示习惯动作 |
Fish will die without water. |
|
表示预言 |
Oil will float on water. |
|
would |
表示意志或愿望 |
Try as he would, he couldn't succeed. |
|
表示请求，比will更婉转 |
Would you give me a hand? |
|
表示过去的习惯动作 |
When he was young he would always stay up late. |
|
用于虚拟语气 |
If I were you I would try it again. |
1 语法辨析
Incorrect: "Need I to eat it all, Mummy?""Yes, you need."
Correct: "Need I eat it all, Mummy?""Yes, you must."
* need用在疑问句或否定句中常用作情态动词，其后接不带to的不定式。由need提问的疑问句的答语如是肯定句时要用must。 肯定句中 need 常用为实意动词,如:I need to wait for my boy. (这时要加to)
Incorrect: You did told me to do it, didn't you?
Correct: You did tell me to do it, didn't you?
* do用在肯定句的动词之前表示加强口气，其后要跟动词原形。
Incorrect: I'll have my TV set repair tomorrow.
Correct: I'll have my TV set repaired tomorrow.
* have +人+动词原形为让某人做某事。而have+物+过去分词为某件事让别人去做(而不是句子主语所表示的人自己干的事)。这句话应译为我明天打算将电视机送出去修理。
Incorrect: I'll get my brother help you next time.
Correct: I'll get my brother to help you next time.
* 要注意 have 与 get的不同用法，如，have somebody do something 则要用getsomebody to do something, 但是have somebody doing something 用get 时句型是一致的,即get somebody doing something。 在have something done 表达法也可以将have 换为get, 即get something done。
Incorrect: I have to work on Sunday, but I haven't to work a fullday.
Correct: I have to work on Sunday, but I don't have towork a full day.
* have to 意为不得不做某事，其否定式应为don't have to。
Incorrect: Do you see the smoke? Yes, something must havebeen
burning.
Correct: Do you see the smoke?Yes, something must be burning.
* must 加原形动词，是对现在某事有把握的推测，而must 加be+ing形式则是表示即将发生或正在发生之事，must 加have 加p. p.(过去分词)，则表示对过去事情的推测。
Incorrect: Someone knocks the door. Must it be the boss?
No, it mustn't be the boss.
Correct: Someone knocks the door.Can it be the boss!No, it can't be the
boss.
* 在表示推测的疑问句和否定句中不能用must 而要用can。
Incorrect: I cannot but doing this homework again.
Correct: I cannot but do this homework again.
Incorrect: I cannot help to laugh.
Correct: I cannot help laughing.
* "不得不"，"不可避免"，"不禁"的表达法有两个:其一cannot
but 加动词原形，其二 cannot help 加动名词。
Incorrect: I would go to the Great Wall five or six times last year.
Correct: I went to the Great Wall five or six times last year.
* 当指在过去某个动作发生了若干次时，不可用would和used to, 因为would 和used to 表示过去的某种习惯，而would 则多用于不规律的动作，而used to则多用于一种习惯性的状态。
Incorrect: I would rather you do it alone.
Correct: I would rather you did it alone.
Correct: I would rather do it alone.
* would rather 其后接不带to的不定式，但如果是从句时，从句中的谓语动词要用过去式。
Incorrect: He dares not tell his parents about his failure in the exam.
Correct: He dare not tell his parents about his failurein the exam.
* dare 在这里用作情态动词，所以主语虽是人称单数，但dare不要加"s"。
Incorrect: When you go abroad, do you must apply for a passport?
Correct: When you go abroad, do you have to apply for a passport?
* must 与 have to 都可以表示必须。但在实际用法上还是有一定区别的，如must是含有上级的命令，说话人坚持要作的某些事情，而have to表示由于环境条件，习惯的约束而不得不去做的事。
Incorrect: My grandma is over seventy but she is able to read without glasses.
Correct: My grandma is over seventy but she can read without glasses.
* can (could) 表示主观能力，客观实际。be able to 则表示主观意愿。这句话应译为我的祖母已七十多岁了，但她仍能不用带眼镜看书。
Incorrect: She doesn't answer the doorbellShe should beasleep.
Correct: She doesn't answer the doorbellShe might be
asleep.
* should用于现在时的句中表示应该，而might用于现在时的句中表示有可能，其可能性比must要小些。
Incorrect: You hadn't ought to have done silly things
Correct: You ought not to have done silly things
* ought to的否定式是ought not to。
Incorrect: "Do you like some hot coffee now?"
Correct: "Would you like some hot coffee now?"
* Do you like 问的是习惯,如:Do you like swimming every day?而would you like是一次性的邀请。
2 例题解析
［例1］"After I fill out this application form,what is the next thing to do?"
"Then you go to the registrar's
office."
A. can B. must C. have to D. should
［答案］C． have to是客观要求所必作之事。
［例2］He was a good runner so he escape from the
police.
A. succeeded to B. might C. was able to D. could
［答案］C． be able to表达说话人的主观意愿要去做的事，而can只表示客观上的能力，而不表示意愿。
［例3］To travel from England to Scotland you a
passport.
A. mustn't have B. haven't got
C. don't need D. needn't
［答案］C． 这里need作实意动词而不是情态动词。
［例4］"You'd better go to the theatre. You're an hour late already."
"I wouldn't dare in now."
A. be going B. the going C. go D. that I go
［答案］C． 作实意动词的dare 在否定句中可以用to， 也可以不用to.
［例5］"I haven't felt well for a week."
"You see a doctor."
A. had ought to B. had better
C. should have to D. had rather
［答案］B． had better 意为最好，而would rather 为宁可，had better的否定式had better not， 疑问句为Had you better…?
［例6］You eat it, it is poisonous.
A. mustn't B. may not C. needn't D. can't
［答案］A． 因mustn't 表示禁止，一定不许做某事。
［例7］I tried to persuade him not to drinkso much, but he
listen to me.
A. wouldn't B. couldn't
C. had better not D. used to
［答案］A． 由于转折连词but，所以C、D选项不合句意， wouldn't 为 will的过去时否定句，所以带有意愿之意。应译为但他不一定愿意听我的忠告。
［例8］You go shopping this weekend,for there's enough food at
home.
A. wouldn't B. mustn't C. can't D. needn't
［答案］D． needn't意为没有必要。
［例9］Don't throw the book away. It in the future.
A. might be needed B. may need C. is needed D. needs
［答案］A． might表示一种可能性。
［例10］I watch TV at home than go to the concert.
A. would prefer B. would better
C. had better D. would rather
［答案］D． 此句中有than所以根据题意应选择D。
would rather…than意为宁愿做某事而不愿去做另一件事。
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