unit 1 Festivals around the world 情态动词
Unit-1-Festivals-around-the-world-课文知识点解析1
7....when people should go to clean the graves and light incense in memory of their ancestors.
……这时候，人们去扫墓，点上香火祭祀祖先。
memory[ C usually plura] n. 表示所记住的事情，记忆
starve vt.&vi. 挨饿，饿死
e.g. Thousands of people will starve if food doesn’t reach the stricken city.
假如食物无法到达这座受灾的城市，成千上万的人将会饿死。
5.They lit fire and made music because they thought these festivals would bring a year of plenty.
他们把食物, 鲜花和礼物献给死者。
offer sth. to sb.= offer sb.sth.供应某物给某人
e.g. He offered me 300 dollars for that television.
他出300美元向我买那部电视机。
12.The festival of Halloween had its origin as an event in memory of the dead.
万圣节起源于纪念已逝的人们。
had its origin as an event 起源于某事
have your or its origin=begin 开始
e.g.Many of the problems had their origin in post-war Europe.
英语Unit1《Festivals around the world》语法情态动词(新人教版必修3)
英语：Unit1《Festivals around the world》语法情态动词（新人教版必修3）Modal verbs（情态动词）教师寄语：Just put one foot in front of the other and God will do the rest.may / might, can / could, will / would, shall / should, must / can的用法。
1.may 与might的用法2. can与could的用法3. will与would的用法4.shall与should的用法5. must, may (might) 和can表示“推测”的用法跟踪练习I. 单项填空：1.Write in simple English in order that everybody ______ understand you.A. mayB. mustC. shouldD. will2.You _______ miss the lecture, though you ______ have it.A. mustn’t; needn’tB. needn’t; mustn’tC. mustn’t; mustn’tD. can’t; needn’t3.--- Better not have the operation right now.--- ________.A. I mustn’tB. I shouldn’tC. I won’tD. I can’t4.The train was ten minutes late, so I ______ have run all the way from my house to the station.A. couldn’tB. shouldn’tC. needn’tD. mustn’t5.I’m not going simply because I don’t see why I _______.A. willB. wouldC. shouldD. shall6.--- It must be Mr. Li who did it.--- No, it _____ be Mr. Li.A. mustn’tB. can’tC. wouldn’tD. may7.--- It’s getting cloudier and cloudier.--- Yes, I’m afraid it ______ be raining soon.A. mustB. shouldC. mightD. can8.I promised to get there before 5 o’clock, but now the rain is pouring down. They _____ for me impatiently.A. mat waitB. ought to waitC. could waitD. must be waiting9.--- ______ you make so much noise?--- Sorry, I’ll take care not to.A. Must;B. CanC. MayD. Would10.On Sundays when I was a child, Father and I _____ get up early and go fishing.A. couldB. wouldC. mightD. should11.I ______ have written to him because he phoned me shortly afterwards.A.ought toB. mustC. couldn’tD. needn’t12.--- _____ the plane have taken off on time?--- I’m afraid not. The fog was too thick then.A. NeedB. ShouldC. CanD. Must13.This looks like a different kind of stone. What _____ we do with it?A. willB. shallC. wouldD. do14.He has much money at the beginning of every month, but by the end of it he _____ little left.A. can haveB. will haveC. should haveD. need have15.How _______ you say that you really understand the whole story if you have finished only part of the article?A. mustB. needC. mayD. canII. 用适当的情态动词填空：1.There is 20 minutes left. We _______ (not) have to be in such a hurry.2.Where is my watch? I really can’t find it. Where _____ it be?3.The doctor told the old man that he ______ avoid eating fat.4.It’s too late. I think he ______ go to bed.5.______ you mind my troubling you with a few questions?(Keys: 1. A 2. A 3. C 4. C 5. C 6. B 7. A 8. D 9. A 10. B 11. D 12. C 13. B 14. B 15. D )(Keys: 1. needn’t 2. can 3. should 4. must 5. Would )。
高一英语Unit 1 Festivals around the world (2) 人教实验版知识精讲
高一英语Unit 1 Festivals around the world (2)人教实验版【本讲教育信息】一. 教学内容：Unit 1 Festivals around the world (2)情态动词的用法can / could may / might will / would shall / should must/ need二. 重、难点讲解1. 情态动词的概述1）英文中常用的情态动词有：can / could, may / might, shall / should, will / would, must, had better, need等。
2）情态动词有别于助动词（be, have, do）, 情态动词有其自身的词汇意义，而且通常是一词多义。
用来表示可能、建议、愿望、必要、允许、能力、怀疑等。
3）在谓语中的作用：情态动词在句中不能单独作句子的谓语，必须和实义动词一起构成复合谓语。
如：I must go to school today.He can dance.He can’t swim.2. 情态动词及其基本含义can, could, be able tomay, mightmust, have toshall, should, ought toneed, darewill, would1）can / could表示“能够”或表示委婉客气地提出问题或陈述看法表示“能够”（注意与be able to的差别）a. 表示现在的能力，常用can, 而不用be able to. 如：Bob can play the piano.A fish can’t walk, but it can swim.b. could 表示过去“一般的能力，总的能力”，即我们在过去想干什么就随时可以干什么。
这里也可以用was / were able to.如：I could / was able to recite several poems when I was 3 years old.而表示主语在过去某个特定的场合所表现出的“特定的能力，具体的能力”，或表示某人在某一场合成功地完成了某件事，要用was / were able to.如：With the aid of the wood, he was able to swim across the river.He hurried to the station, and he was able to catch the train.c. 在否定句中，could 和was / were able to 可以互换。
B3U1 Grammar-情态动词 Festivals around the world
一 can和could
用法
例句
表示能力
1．“I don’t think Mike can type.” “Yes, he can.” 2．I can speak fluent English now , but I couldn’t
last year.
表示对现在的动作或状态
1.It can’t be easy caring for a man and a child
1.You mustn’t go there. 2.You don’t have to go there.
注意：must 表示”偏要，硬要，一定要，坚持要做某事 -how old are you, madam?
-If you must know, I’m twice my son’s age.
如果你非得知道，是我儿子年龄的两倍
1.Might I borrow your pen?
2.I wonder if I might speak to your son.
1.It may rain this afternoon. 2.She might come to join us this afternoon. 3.I suppose he might have missed the train.
as well+动词原形”意为“最好，2.You may as well tell us now, we’ll find out
满可以，倒不如”，相当于 “had better.
sooner or later. 3.I suppose we might as well go home.
1.A computer ____ think for itself; it must be told what to do. A. can’t B. couldn’t C. may not D. might not
【语法讲解】Unit1Festivalsaroundtheworld精讲语法
【语法讲解】Unit 1 Festivals around the world 精讲语法情态动词（I）一、概述情态动词表示说话人的某种感情或语气，对某一动作或状态的某种态度，表示“需要”“可以”“必须”“应当”等意义。
情态动词有以下特征：1. 不能单独作谓语，除ought to和used to以外，后面只能接不带to的不定式。
2. 没有人称和数的变化。
但有些情态动词，如can, will, dare有一般时和过去时的变化。
3. 情态动词的“时态”的形式并不是区分时间的主要标志。
不少情况下，情态动词的现在时形式和过去时形式都可用来表示现在时间、过去时间或将来时间。
二、用法归纳1. can和could(1)表示能力，常译为“能，会”。
e.g. I can speak Japanese, but I can't write it. 我会说日语，但是不会写。
(2)表示允许，常译为“可以”；could还可以表示更加委婉地请求或许可。
e.g. —Can/Could I have a look at your photos? 我可以看看你的照片吗？—Of course you can.当然可以了。
You can smoke in this room. 你可以在这间屋子里吸烟。
(3)表示对现在或过去情况的推测，只用于疑问句或否定句中。
e.g. —Can she be in the classroom? 她可能在教室吗？—No, she can't be in it. 不，她不可能在教室里。
Can what he said be true? 他说的可能是真的吗？(4)用于肯定的陈述句中，表示理论上或习惯上的可能性。
e.g. Accidents can happen at any time.事故随时会发生。
It could be very interesting to go out for a drive.出去开车兜风可能会很有趣。
Festivals Around the World
can/could
1. 表示能力 Can you speak Japanese? 2. 表示推测时，只用在否定句或疑问句中。 He can’t be at home now? 3. 表示允许（许可或请求许可） You can go now, but he can’t. 4. 表惊异、怀疑等。 How can you be so rude? Could 可表示能力或可能性，多用于过去，也可指现在，通常 表示虚拟或作为can 的委婉形式。
Festivals around the world
情态动词
情态动词的语法特征：
1. 情态动词有一定的意义，表示或暗示某种情绪或态 度，表示可能、建议、愿望、必要、允许、能力等。 2.情态动词没有人称和数的变化，即不随主语的不同 而变化。 3.情态动词不能独立使用，必须和是一动词一起构成 谓语。 4.情态动词除了ought和have外，后面只能接不带to的 不定式。 5.情态动词没有非谓语形式，即没有不定式、分词等 形式。
He can’t have been to that town.
他不可能去过那个城。
May/might
1. 表示可能性，might 比may 可能性更小。 It may be true. He might not come today. 2. 表示请求、许可，多用于肯定和疑问句中 May I ask you a question? 3. 表示愿望 May you be happy all your life. might 比may 语气更委婉 May/might 表示推测时，表示对现在或将来要 发生的事情把握不大。
3. Should 常用于表示应当，意思接近ought to，但语 气较弱。 Young people should learn how to use computers. 4.Should 用于可能性推测时，表“应该，很可能” They left at 5:30. They should get there now. 5.Should have done 表示责备或批评，为“本应该 ……但” You should have told her the truth earlier.
高中英语 Unit1 Festivals around the world 情态动词课件 新人教版必修3
4. should
1. 用于表劝告、建议。 意为”应该、应当”。 用于表劝告、建议。 意为”应该、应当” Eg: You should keep your promise. 2. 用于表推测。 意为 “可能、该…” 用于表推测。 可能、 Eg: 1) It’s 7 o’clock, he should be at home. 2) They should have arrived by now.
3.表示习惯性动作。 译作 “总是、惯于” will 指现在， 表示习惯性动作。 总是、惯于” 指现在， 表示习惯性动作 would 指过去。 指过去。 Eg: 1)He will often read all night. 2) Fish will die without water. 3) Every evening, she would sit by window, deep in thought. 4. 表示功能，译作“能、行” 表示功能，译作“ Eg: 1) That will be all right. 2) This door won’t open. 5. 用于否定句中，表示“不肯、不乐意” 用于否定句中，表示“不肯、不乐意” Eg: No matter what I said, he won’t listen to me.
B 1. Michael ____ be a policeman, for he’s much too short. A. needn’t B. can’t C. should D. may A 2. Mr. Bush is on time for everything. How ____ it be that he was late for the opening ceremony? A. can B. should C. may D. must 3. ---- I stayed at a hotel while in New York. ---- Oh, did you? You ____ with Barbara. A A. could have stayed B. could stay C. would stay D. must have stayed 4. My sister met him at the Grand Theater yesterday A afternoon, so he ____ your lecture. A. couldn’t have attended B. needn’t have attended C. mustn’t have attended D. shouldn’t have attended
高中英语Unit1FestivalsaroundtheworldSectionⅣGrammar_情态动词Ⅰ课件新人教版必修
[语法详解] 一、概述 情态动词表示说话人的语气或情绪，如可能、意愿、猜测、义 务、需要等。 情态动词有以下特征： 1．有一定的词义，但不能单独作谓语，后面接动词原形。 2．没有人称和数的变化(have to 除外)。 3．多数情态动词都有过去式，如 can－could，may－might， will－would，dare－dared 等。情态动词的“时态”并不是区分时间 的主要标志。很多情况下，情态动词的原形和过去式都可用于多种 时态。
二、用法归纳 1．can 与 could (1)表示能力，常译为“能，会”。could 是 can 的过去式，表 示过去的能力。 I can speak English and French，but I can't speak Japanese. 我会讲英语和法语，但是不会讲日语。 When she was 8 years old, she could play the piano very well. 当她八岁时，她就能很好地弹钢琴了。
(3)表示推测，意为“可能”，常用于否定句和疑问句中。 —Can the lady over there be our boss? ——在那边的那位女士可能是我们的老板吗？ —It can't be her. I saw our boss in the office just now. ——不可能是她。我刚刚看见我们的老板在办公室里。 My glasses aren't here. Where can I have put them? 我的眼镜不在这里。我可能把它们放哪儿了呢？
③“can't＋help＋动名词”表示“禁不住做某事”。 When hearing that，every one of us could not help laughing. 我们大家听到那件事都忍不住笑了。 ④“can't ＋ (choose/help)but ＋动词原形”表示“不得不 ， 只 好”。 He can't choose but buy his girlfriend flowers. 他不得不给他女朋友买花。
Unit 1 Festivals around the world 情态动词
1. “cannot …too…”表示“无论怎么……也不（过分）”。 You cannot be too careful in crossing the street. 过马路越小心越好。 You cannot praise him too much. 你怎么表扬他都不过分。 I can never thank him enough. 我对他感激不尽。 2. “can’t help doing sth”表示“不禁，忍不住，不得不（做某 事）” Hearing the news, I can’t help laughing. 3. “can’t help but do sth”表示“不禁，忍不住，不得不” I can’t help but be sorry about it. 我不能不为之感到遗憾。 I cannot help but admire her courage. 我情不自禁地钦佩她的勇气。 4. “cannot but do sth”表示“除此 之外，别无他法，”。 I couldn’t but laugh on his funny face. 看到他那张滑稽的脸，我只能笑了笑。
3.I suppose we might as well go home.
1.A computer ____ think for itself; it must be told what to do. A. can’t B. couldn’t C. may not D. might not 2. I thought you ________ like something to read, so I have brought you some books. A. may B. might C. could D. must
1.Can this be an excuse for not giving them help? 2.This can’t be true. 3.How can you be so crazy.
Festivals around the world-grammar
Although the soldier was badly wounded, he was able to tell what had happened. 表示过去的能力 She ran fast but she couldn’t /wasn’t able to catch the bus. 3.表示特定的某一过去能力或表示成功地做了某 事时，只能用was/were able to， 不能用could。
7.--Excuse me, but I want to use your computer to type a report. --You _A___ have my computer if you don’t take care of it. A. shan’t B. might not C. needn’t D. shouldn’t
3） 情态动词的“时态”形式并不是时间区别的主要 标志，不少情况下，情态动词的现在式形式和过去式 形式都可用来表示现在时间、过去时间和将来时间。
can, could 和be able to的用法
1.can, be able to都可表示“能力” Can的主语是人或物,be able to的主语是人
Unit1 Festivals around the world
Grammar
Modal verbs 情态动词 (I)
·情态动词的语法特征
1） 情态动词 不能单独做谓语，除ought 和have 外， 后面只能接不带to 的不定式。
2） 情态动词没有人称，数的变化，但有些情态动 词，如can、will也有一般式和过去式的变化。
was busy cooking the dinner. Of course，after I gave her my advice，she must go and do the opposite。
高中英语 Unit 1 Festivals around the world Part Ⅲ Gram
Part ⅢGrammar & WritingGrammar——情态动词(Ⅰ)一、概念情态动词本身有一定的词义，表示说话人的某种感情或语气，对某一动作或状态的某种态度，表示“需要”“可以”“必须”“应当”等意义。
二、基本特征1．情态动词有一定的词义，不能单独作谓语，需和实义动词或系动词一起作谓语。
She can speak English fluently though she is five.尽管她才5岁，但她说英语流利。
2．情态动词一般无人称和数的变化，个别情态动词有现在时和过去时两种时态变化。
Mary must be in the library.玛丽一定在图书馆。
3．构成否定句时，not放在其后面。
The young man can't carry the big stone.这个年轻人搬不动那块大石头。
4．情态动词后接动词原形。
You will do as I told you.你得照我说的去做。
三、基本用法1．can与could的用法(1)表示能力：can用来表示现在的能力，could表示过去的能力。
I can play basketball now, but I couldn't when I was young.现在我会打篮球了，但小时候我不会。
(2)表示请求和许可：could语气比can委婉，但回答时只能用can。
Can/Could you lend me a hand?你能帮我一下吗？(3)表示推测，意为“可能”，多用于否定句或疑问句。
—Can he be in the reading room now?—No, he can't be in it. Because I saw him in the office just now.——他现在可能在阅览室吗？——不，他不可能在(阅览室)。
因为我刚刚在办公室看见他了。
(4)表示推测，意为“有时会”，常用于肯定句中。
人教版高中英语必修3新人教版必修三Unit 1 Festivals around the world 语法情态动词
情态动词情态动词表示说话人的语气和情态。
如需要、可能、愿意、怀疑等。
情态动词有一定的词义，但不完整，必须和主要动词的原型一起构成谓语。
常用的情态动词有：can, could, may, might, must, have to, ought to, need, dare, shall, will, should, would, be able to,及半情态动词be to do, had better等。
情态动词的基本用法：（一）can“能够”1.表示体力或脑力方面的能力，或根据客观规律能做某事的能力。
如：I can go there now.(1)can表“能够”时，既可指现在也可指将来。
(2)can与be able to的区别：①表“能力”时二者同义No one can / is able to do it.②be able to常侧重经过努力有能力做到，有多种时态。
can侧重自身的能力，只有一般现在时和一般过去时。
③was / were able to do表示通过努力克服困难或在一定的条件下成功地做了某事，侧重结果，相当于managed to do或succeeded in doing...。
could仅表自身的能力或本领，但未必成功做到。
With the help of the firemen, they were able to leave the burning house.He was able to swim across the river.In the end, we were able to rescue the workers trapped in the fire.2.表示“许可，允许”。
在疑问句中表示请求，许可；否定句中表示“不许”。
此时常与may 通用：May/Can I do it?This sort of thing can't go on! 这类事情不能再继续了！can not有时可以表示“禁止”相当于mustn't：You can't（mustn't，are not allowed to）play football in the street.你不可以在大街上踢球。
unit1-festivals-around-the-world-grammar(教学课件201909)
can, could 和be able to的用法
1.can, be able to都可表示“能力” Can的主语是人或物,be able to的主语是人
She can/be able to sing the song in English. This machine can make you feel comfortable.
2.can只用于现在式和过去式(could)。 be able to可以用于各种时态。 We’ll be able to finish the work soon. I haven’t been able to see the film. could用于表示泛指过去的能力。如： I could read when I was four.
Unit1 Festivals around the world
Grபைடு நூலகம்mmar
Modal verbs 情态动词 (I)
·情态动词的语法特征
1） 情态动词 不能单独做谓语，除ought 和have 外， 后面只能接不带to 的不定式。
2） 情态动词没有人称，数的变化，但有些情态动 词，如can、will也有一般式和过去式的变化。
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unit1-festivals-around-the-world-grammar(教学课件201911)
2.can只用于现在式和过去式(could)。 be able to可以用于各种时态。 We’ll be able to finish the work soon. I haven’t been able to see the film. could用于表示泛指过去的能力。如： I could read when I was four.
Although the soldier was badly wounded, he was able to tell what had happened. 表示过去的能力 She ran fast but she couldn’t /wasn’t able to catch the bus. 3.表示特定的某一过去能力或表示成功地做了某 事时，只能用was/were able to， 不能用could。
Unit1 Festivals around the world
Grammar
பைடு நூலகம்Modal verbs 情态动词 (I)
·情态动词的语法特征
1） 情态动词 不能单独做谓语，除ought 和have 外， 后面只能接不带to 的不定式。
2） 情态动词没有人称，数的变化，但有些情态动 词，如can、will也有一般式和过去式的变化。
He was able to flee Europe before the war broke out. He was able to swim halfway before he got tired.
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高一英语3学案：语法详解Unit1 Festivalsaroundtheworld含解析
四、语法详解情态动词情态动词是动词的一种，表示说话人的情感或态度。
情态动词没有人称和数的变化.情态动词不能单独作谓语，必须和动词原形连用，共同构成谓语动词，有些情态动词有过去式，有些则没有。
如:can —could，may-might，shall-should,will—would，have to—had to,dare-dared，但must,need，ought to,had better则只有一种形式.1。
can和could（1）表示“现在的能力”用can,“过去的能力”用could.如：We can use the computer now,but we couldn’t 10 years ago.(2）表示许可或征询对方的许可，可用can或could（语气委婉，不表示过去)，用may较正式，注意回答时不用could。
如：—Can/Could/May I come in？—Yes,you can/may.（3）表示“可能性”时can多用于否定句和疑问句，表示“不可能”“可能吗？”，肯定句多用could,may，might。
如：The story could/may/might be true.It can’t be true。
（4）can和be able to都可表示能力，但be able to强调经过努力，克服困难，从而能够.如：The maths problem was very difficult,but he was able to work it out.活学巧用1.单项填空（1）(2005浙江高考，9)The World Wide Web is sometimes jokingly called the World Wide Wait because it _________ be very slow.A。
should B.must C.can D.need提示：can作为情态动词可以表示一时的情况，意为“有时候会"。
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1．“I don’t think Mike can type.” “Yes, he can.” 2．I can speak fluent English now , but I couldn’t last year. 1.It can’t be easy caring for a man and a child who are not your own. Can the man over there be our head master?
三．must和have to
情态动词 用法 例句
1.You must come to school on time.
表示“必须，应该”之意，语气比should， 2.Everybody must obey the law. ought to强烈。其否定形式mustn’t表示 3.You mustn’t drive so fast in the street. “不准，不应该，禁止”等意
情态动词
用法
表示允许、许可。否定回答一般 用must not/mustn’t,表示“禁止、 阻止”之意，但也可以用had better not (最好别)或may not （不可以），语气较为委婉。 在表示请求、允许时，might比 may语气更委婉些。用May I征询对 方许可在文体上比较正式，在日常 用语中，用Can I征询对方意见更为 常见。 表示可能性的推测，通常用在肯定 句和否定句中，含有“或许”“大 概”“可能”之意；用might代替 may时，则语气显得更加不肯定。
3.I suppose we might as well go home.
1.A computer ____ think for itself; it must be told what to do. A. can’t B. couldn’t C. may not D. might not 2. I thought you ________ like something to read, so I have brought you some books. A. may B. might C. could D. must
1. “cannot …too…”表示“无论怎么……也不（过分）”。 You cannot be too careful in crossing the street. 过马路越小心越好。 You cannot praise him too much. 你怎么表扬他都不过分。 I can never thank him enough. 我对他感激不尽。 2. “can’t help doing sth”表示“不禁，忍不住，不得不（做某 事）” Hearing the news, I can’t help laughing. 3. “can’t help but do sth”表示“不禁，忍不住，不得不” I can’t help but be sorry about it. 我不能不为之感到遗憾。 I cannot help but admire her courage. 我情不自禁地钦佩她的勇气。 4. “cannot but do sth”表示“除此 之外，别无他法，”。 I couldn’t but laugh on his funny face. 看到他那张滑稽的脸，我只能笑了笑。
1．—Must I come back before ten? —Yes，you must. ----No, you needn’t (No, you don’t have to) 1.It must be my mother. 2.You must be hungry after a walk. 3.There must be a hole in the wall. 1.The film is not interesting. I really must go now. 2.I have to go now, because my mother is in hospital. 1．I had to work hard when I was your age. 2．I will have to learn how to use a computer. 3．In order to take the exam, we’ll have to finish the whole book by the end of this month .
have to
must只有一种形式，即现在式与过 去式都是一种形式，而have to则涉 及各种人称、时态等方面的变化形 式。 两者的否定意义不同，mustn’t 表示“禁止，不许”，don’t have to表示不必。
1.You mustn’t go there. 2.You don’t have to go there.
例句
1.May I come in and wait? 2.——May I smoke here? ——No, you mustn’t(或No, you’d better your pen? 2.I wonder if I might speak to your son. 1.It may rain this afternoon. 2.She might come to join us this afternoon. 3.I suppose he might have missed the train.
may might
may用于祈使句表示祝愿
1.May you succeed. 2.May you live happily! 3.May she rest in peace.愿她安息。
惯用句式： 1.There is nothing to do, so I may as well go to “may as well或might (just) bed. as well+动词原形”意为“最好，2.You may as well tell us now, we’ll find out 满可以，倒不如”，相当于 sooner or later. “had better.
语法 ：情态动词
Grammar: Modal Verbs
情态动词 Modal Verbs I 情态动词的定义 情态动词是一种本身有一定的词义，表示说话人的情绪、态度或语气的动词， 但不能单独作谓语，只能和其他动词原形构成谓语。 情态动词数量不多，但用途广泛，主要有： can (could), may (might), must, need, ought to, dare (dared), shall (should), will (would) . II 情态动词的位置 情态动词在句中放在谓语动词之前，谓语动词前若有助动词，则在助动词之前， 疑问句中， 情态动词放在主语之前。 I can see you. Come here. 我能看见你，过来吧。 He must have been away. 他一定走了。 What can I do for you? 你要什么？ How dare you treat us like that! 你怎么敢那样对待我们! Ⅲ 情态动词的语法特征 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。
2.表示推测时，could不是过去式，只是语气更委婉；若是推测已发生的事或过去的情况， 用can/could have done 3.can和be able to辨析 can (could) 和be able to都可以表示能力，意思上没有区别。但can只有现在式和过去 式，而be able to则有更多的形式。如： I’ve always wanted to be able to speak fluent English. Those bags look really heavy, are you sure you’ll be able to carry them on your own? 但是，表示在过去某时的某一场合经过一番努力，终于做成了某事，通常不用could， 而用was/were able to来表示。这时，was/were able to相当于managed to do或 succeed in doing。如： After the accident it was a long time before she was able to walk again. The fire was very big, but most people were able to escape from the building.
1.Can this be an excuse for not giving them help? 2.This can’t be true. 3.How can you be so crazy.
特别说明： 1.could用来表示请求时，语气委婉，主要用于疑问句，不能用于肯定句，答语应用can （即：could不能用于现在时态的简略答语中）。如： ——Could I use your dictionary? ——Yes, you can.(否定回答可用：No, I’m afraid not.或者是you can’t)
4.We mustn’t waste any more time.
must
在回答带有must的问句时，否定回 答常用needn’t或don’t have to，表 示“不必”，而不用mustn’t 表示有把握的推测，意为 “一定、准是”，只用于肯 定句中
“必须，不得不”，意义与must相近。 但must表示的是说话人的主观看法，而 have to则往往强调客观需要。
注意：must 表示”偏要，硬要，一定要，坚持要做某事 -how old are you, madam? -If you must know, I’m twice my son’s age.