§ 专题一 情态动词和虚拟语气 §
1 情态动词的用法
一、情态动词的语法特征。
情态动词和助动词一样，都是辅助性的动词,用来帮助构成不同的时态和语态，表示说话者的某种情态，没有人称和数的变化。情态动词主要有can, may， must, could, might, shall , should, will， would， ought to， need， dare等。
1、情态动词不能表示正在发生或已经发生的事情，只表示期待或估计某事的发生。
2、情态动词 除ought 和have 外,后面只能接不带to 的不定式，即动词原形。
3、情态动词没有人称，数的变化,即情态动词第三人称单数不加—s.
4、情态动词没有非谓语形式,即没有不定式，分词等形式。
二、情态动词的基本用法。
1、can， could
（1)表示能力，意为“能,会”：The smallest good habits can make a big difference。［福建2014]
It was veral minutes before I could take in what he was saying。［湖北2014}
(2)表推测,意为“可能”，用于否定句或疑问句中，can比could语气强:This can't/couldn’t be done by him。
（3）表示请求或允许，在疑问句中可以用could代替can，语气更委婉。
Could I u your phone,plea？
（4）表示理论上的可能性.Always believe that good things are possible，and remember that mistakes can be lessons that lead to discoveries.
（5)用于否定句或疑问句，表示惊异、怀疑、不相信等态度。
He can’t do this. / Can this be done by him？
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(6）用于固定习语中：can't.。。too/enough表示“无论.。.也不为过”；can’t help doing sth表示“禁不住做某事”：You can’t be too慈禧的儿子是谁 careful while driving. / Hearing the story，I couldn’t help laughing.
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【易混易错】can和be able to的区别：
（1)都可以表示能力，有时可以互换。
（2）be able to可以表示“终于做成某事”有更多时态和人称的变化，还可以与某些情态动词或系动词连用，如might,ought to，em等，be able to还可以用非谓语动词形式。
He 舟过吴江emed to be able to put complicated thoughts in simple words.
She grasped my hand，not being able to say anything.
2、may，might
(1）表示请求和许可，疑问句中可互换，might语气更委婉。Might I borrow your computer？
(2）表示可能性，可以对现在、将来或过去进行推测，通常用于肯定句和否定句，might比may语气弱.
Parents 清算审计may scold their children when they are untidy but they should also understand that their room is their own private space.［广东2014]
(3）表示祝愿，常用结构为“May+主语+Vo”.批评拼音
(4)用于固定习语中“may/might as well + Vo”意为“不放,倒不如，最好"；“may/might well do+Vo"意为“最好做”。
【易错警示】 may作“可以”讲时，其否定回答用mustn’t，表示“不可以，禁止”.
——May I u your car？ --No，you mustn’t.
3、must
（1）表示义务，意为“必须"（主观意志）回答must的一般疑问句时，若是否定回答，不用mustn't,而用needn’t/don't have to,表示“不必”的意思.
【易混辨析】must和have to的区别：
1)must表示出于主观意识必须要做某事，have to表示由于某种客观原因而不得不做某事，除此之外，have to自身有人称和时态的变化:It was then that I started to appreciate the tough choices she had to make on comparing her family and work.［天津2014］
2)have to 表示义务或习惯动作，must表示重要或急迫的事情。
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She has to be at the office before eight every day。
You must go to the manager at once, or you’ll be dismisd。
(2）表示猜测，推测，意为“一定”。常用于肯定句；对现在或未来的事情推测用must do,对正在进行的事情推测用must be doing，对过去发生的事情推测用must have done结构。
He thought Joe must be dead，but he didn’t want to leave immediately.［课标全国2014］
Hurry up！ They must be waiting for us now.
（3）用于否定句表示禁止。Smoking must not be allowed in the office.
（4）表示“偏要，非要.。。不可"。Must you make so loud noi？
4、shall
（1）用于第一、第三人称疑问句，表示征求对方的意见或请示。
Shall I tell Brett to come over straight after school tomorrow？［江西2014]
（2)用于第二、三人称的陈述句，表示说话人给对方的命令、警告、允诺和威胁。
I promi he shall get a prent for his birthday。
(3）用于条约、法令、法律、规定等，意为“必须”。
It has been announced that candidates shall remain in their ats until all the papers have been collected.
5、should,ought to
（1)表示责任、义务、劝告、建议等，意为“应该”，表示责任或义务时，ought to=should，只是前者语气更重。
Why shouldn’t we buy the lady a flower？I will make her feel better.［陕西2014]
You ought not to向此德 be so lfish。
（2)should表示出乎意料的语气,意为“竟然，居然”。
That he should speak to you like that is quite astonishing.
→用在I’m surprid， it worries me， it’s a pity, it’s unthinkable等结构后面的句子中表示惊讶、忧虑、惋惜、欢欣等情绪.
I’m surprid that he should eat so little every day.
It's a pity that she should fail in the entrance examination.
（3）should表示根据经验或常理的推断：The watch should be OK tomorrow。
（4）should和ought to表示推测，指预期的可能性，意为“应该,估计"
He ought to/should be here on time-he started early enough.
6、will，would
（1）用于表示意志或意愿.will指现在，would指过去。
I will never do that again. / They said that they would help us。
(2）表示“请求；建议”。用would比will委婉、客气些,句末用won’t you表达邀请的语气
Will you plea take a message for him? / Would you plea pass him the book？
(3）表示习惯性动作，“总是”“惯于”，will指现 在，would指过去:Fish will die without water.
（4）表示预料或猜想：It would be about ten when he left home。
（5）表示命令、强迫：All will arrive before 7:45
（6)表示意愿或者固执地坚持：She won’t lend me the money。 / The window won’t open
(7）will表示规律性的“注定会"。
Wearing proper clothes is important too,form locals will judge you by what you wear。[重庆2014]
7、need/dare:need/dare可以做助动词，也可以做行为动词
Father nt me the book， so I didn't need to write to him for it.
Father nt me the book， so I needn't have written to him for it.
