[小学英语]英语情态动词用法整理，重难点全覆盖~

定义
情态动词(Modal verbs)本身有一定的词义，表示语气的单词。但是不能独立作谓语，只能和动词原形一起构成谓语。情态动词用在行为动词前，表示说话人对这一动作或状态的看法或主观设想。
情态动词虽然数量不多，但用途广泛，主要有下列：can (could), may (might), must, need, ought to, dare (dared), shall (should), will (would)。
因为情态动词带有某种的情绪性，比如dare就很强硬，比较负面，而may就比较的和善，为了避免在谈话时把“讨论”变成“攻击”，宝贝们一定要学会善用情态动词哦!
下面这张图帮你理清这些情态动词，表示说话者语气的强硬度从高到低依次递减，dare最强硬，shall最温和哦~
分类
情态动词有四类：①只做情态动词：must,can(could),may(might),ought to②可做情态动词又可做实义动词：need,dare③可做情态动词又可做助动词：shall(should),will(would)④具有情态动词特征：have(had) to,used to
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，情态动词则在主语之前。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?我能帮你吗?How dare you treat us like that!你怎能那样对待我们!
特点
情态动词无人称和数的变化, 情态动词后面跟的动词需用原形,否定式构成是在情态动词后面加 "not"。个别情态动词有现在式和过去式两种形式, 过去式用来表达更加客气, 委婉的语气, 时态性不强, 可用于过去，现在或将来。情态动词属非及物动词，故没有被动语态。情态动词没有非谓语形式，即没有不定式，分词，等形式。He could be here soon.他很快就来。We can t carry the heavy box.我们搬不动那箱子。I m sorry I can t help you.对不起，我帮不上你。
基本助动词与情态助动词最主要的区别之一是，基本助动词本身没有词义，而情态助动词则有自己的词义，能表示说话人对有关动作或状态的看法，或表示主观设想：What have you been doing since? (构成完成进行体，本身无词义)I am afraid I must be going. (一定要)You may have read some account of the matter. (或许已经)

除此之外，情态助动词还有如下词法和句法特征：1) 除ought和used以外，其他情态动词后面只能接不带to的不定式。如果我们把ought to和used to看做是固定词组的话，那么，所有情态动词无一例外地只能接不带to的不定式：We used to grow beautiful roses.I asked if he would come and repair my television set.
2) 情态助动词在限定动词词组总是位居第一：They need not have been punished so severely.
3) 情态助动词用于第三人称单数现在时的时候，没有词形变化，即其词尾无-s形式：She dare not say what she thinks.
4) 情态动词没有非限定形式，即没有不定式和分词形式，也没有相应的动名词：Still, she needn t have run away.
5) 情态助动词的“时”的形式并不是时间区别的主要标志。在不少场合，情态助动词的现在时和过去时形式都可以表示现在、过去或将来时间：Would you mind very much if I ask you to do something?She told him he ought not to have done it.
6) 情态助动词之间是相互排斥的，即在一个限定动词词组中只能出现一个情态助动词，但有时却可以与have和be基本助动词连用：You should have washed the wound.Well, you shouldn t be reading a novel.
用法
首先它是动词，而且不同于行为动词，行为动词表示的是可以通过行为来表达的动作(如写，读，跑)，而情态动词只是表达的一种想法(如能，也许，敢)。
用法是：情态动词+行为动词原形例句：I can read this sentence in English.我能用英语读这句话。
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。We can be there on time tomorrow.我们明天能按时去那儿。May I have your name? 我能知道你的名字吗?Shall we begin now?我们现在就开始吗?You must obey the school rules.你必须遵守校规。
功能
助动词(auxiliary)主要有两类：基本助动词(primary auxiliary)和情态助动词(modal auxiliary)。基本助动词有三个：do, have和be;情态助动词有十三个：may, might; can, could; will, would; shall, should; must, need, dare, used to, ought to.上述两类助动词的共同特征是，在协助主动词构成限定动词词组时，具有作用词的功能：
1) 构成否定式：He didn t go and neither did she.The meeting might not start until 5 o clock.
2) 构成疑问式或附加疑问式：Must you leave right now?You have been learning French for 5 years, haven t you?
3) 构成修辞倒装：Nowhere can he obtain any information about his sister.Hardly had he arrived when she started complaining.
4) 代替限定动词词组：A: Who can solve this crossword puzzle?B: Tom can.A: Shall I write to him?B: Yes, do.
用法要点
can, could
1) 表示能力(体力、知识、技能)。Can you lift this heavy box?(体力)Mary can speak three languages.(知识)Can you skate?(技能)此时可用be able to代替。Can只有一般现在时和一般过去式;而be able to则有更多的时态。I’ll not be able to come this afternoon.当表示“经过努力才得以做成功某事”时应用be able to，不能用Can。如：He was able to go to the party yesterday evening in spite of the heavy rain.
2) 表示请求和允许。Can I go now?Yes, you can. / No, you can’t.此时可与may互换。在疑问句中还可用could,might代替，不是过去式，只是语气更委婉，不能用于肯定句和答语中。Could I come to see you tomorrow? Yes, you can. ( No, I’m afraid not. )
3) 表示客观可能性(客观原因形成的能力)。They’ve changed the timetable, so we can go by bus instead.This hall can hold 500 people at least.
4) 表示推测(惊讶、怀疑、不相信的态度)，用于疑问句、否定句和感叹句中。Can this be true?This can’t be done by him.How can this be true?
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)。Could I use your dictionary?Yes, you can.(否定回答可用：No, I’m afraid not.)此时可与may互换。在疑问句中还可用could,might代替，不是过去式，只是语气更委婉，不能用于肯定句和答语中。Could I come to see you tomorrow?Yes, you can. ( No, I’m afraid not. )
(2) 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 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。could：有潜能，但并未做到，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.I can sing many English songs.我会唱许多英文歌曲。We were able to return to our campsite before the heavy rain.我们在下大雨前设法回到了野营地。He was able to swim across the river and escaped being caught.他游到了河对岸，没有被抓住。在否定句中，can/could与be able t几乎没有什么差别，两者可以互换。例如：She wasn’t able to/couldn’t cook French dishes.她不会做法国菜。
(3) 惯用形式“can not …too…”表示“无论怎么……也不(过分)”。如：You cannot be too careful.你越小心越好。惯用形式“can not but+ 不定式(不带to)”表示“不得不，只好”。如：I can not but admire her determination.我不得不钦佩你的决心。

may, might
1) 表示请求和允许。might比 may语气更委婉，而不是过去式。否定回答时可用can’t或mustn’t，表示“不可以，禁止”。Might/ May I smoke in this room?No, you mustn’t.May/Might I take this book out of the room? Yes, you can. (No, you can’t / mustn’t. )用May I...?征徇对方许可时比较正式和客气，而用Can I...?在口语中更常见。
2)用于祈使句，表示祝愿。May you succeed!
3) 表示推测、可能性(不用于疑问句)。might不是过去式，它所表示的可能性比may小。1.He may /might be very busy now.2.Your mother may /might not know the truth.

must, have to
1) 表示必须、必要。You must come in time.在回答引出的问句时，如果是否定的，不能用mustn t(禁止，不准)，而用needn’t, don’t have to(不必).Must we hand in our exercise books today?Yes, you must.No, you don’t have to / you needn’t.
2) must是说话人的主观看法， 而have to则强调客观需要。Must只有一般现在时， have to 有更多的时态形式。1. He play isn’t interesting, I really must go now.2. I had to work when I was your age.
3) 表示推测、可能性(只用于肯定的陈述句)1. You’re Tom’s good friend, so you must know what helikes best.2. Your mother must be waiting for you now.

dare, need
1) dare作情态动词用时, 常用于疑问句、否定句和条件从句中, 过去式形式为dared。1. How dare you say I’m unfair?2. He daren’t speak English before such a crowd, dare he?3. If we dared not go there that day， we couldn’t get the beautiful flowers.
2) need 作情态动词用时, 常用于疑问句、否定句。在肯定句中一般用must, have to, ought to, should代替。1.You needn’t come so early.2.  Need I finish the work today?Yes, you must. / No, you needn’t.
3) dare和 need作实义动词用时， 有人称、时态和数的变化。在肯定句中，dare后面常接带to的不定式。在疑问句和否定句中，dare后 面可接带to或不带to的不定式。而need后面只能接带to的不定式。1. I dare to swim across this river.2. He doesn’t dare (to) answer.3. He needs to finish his homework today.

shall, should
1) shall 用于第一人称，征求对方的意见。What shall we do this evening?
2) shall 用于第二、三人称，表示说话人给对方的命令、警告、允诺或威胁。1. You shall fail if you don’t work hard.(警告)2. He shall have the book when I finish it.(允诺)3. He shall be punished.(威胁)

will, would
1) 表示请求、建议等，would更委婉。Will / Would you pass me the ball, please?
2) 表示意志、愿望和决心。1. I will never do that again.2. They asked him if he would go abroad.
3) would表示过去反复发生的动作或某种倾向。would表示过去习惯时比used to正式，且没有“现已无此习惯”的含义。1. During the vacation, he would visit me every other day.2. The wound would not heal.
4) 表示估计和猜想。It would be about ten o’clock when she left home.

特别说明：
would与used to辨析would可用来表示过去反复出现的动作，但不能表示过去存在的状态，所以我们不能说：“she would be a quiet girl.”另外，would强调过去某种特定情况下的活动，是完全过去的事情，同现在没有联系。而used to则着眼于过去和现在的对比，隐含现在已不存在，动作或状态都可表示。Would可以表示不规则的习惯，used to则不可。如：He used to be a naughty boy and cause trouble.I used to get up at six in the morning.Sometimes she would take a walk in the neighboring woods.In those days, whenever I had difficulties, I would go to Mr. Chen for help.
should, ought to
1) should, ought to表示“应该”，ought to表示义务或责任，比should语气重。1. I should help her because she is in trouble.2. You ought to take care of the baby.
2) 表示劝告、建议和命令。should, ought to可通用，但在疑问句中常用should。1. You should / ought to go to class right away.2. Should I open the window?
3) 表示推测，should , ought to (客观推测), must(主观推测)。1.He must be home by now. (断定他已到家)2.He ought to/should be home by now.(不太肯定)3. This is where the oil must be.(直爽)4. This is where the oil ought to/should be.(含蓄)

情态动词+不定式完成式(have done)
1) can / could + have done在肯定句中表示“本来可以做而实际上能做某事”，是虚拟语气;在疑问句或否定句中表示对过去行为的怀 疑或不肯定, 表示推测。1. You could have done better, but you didn’t try your best.(虚拟语气)2. He can’t have been to that town.(推测)3. Can he have got the book?(推测)
2) may / might +不定式完成式(have done)表示对过去行为的推测。不能用于疑问句中，没有虚拟语气的用法。Might所表示的可能性比may小。1. He may not have finished the work .2. If we had taken the other road, we might have arrived earlier.
3)must +不定式完成式(have done)用于肯定句中，表示对过去行为的推测。意为“一定、想必”。其疑问、否定形式用can，can’t代替。参看1) can / could + have done表示推测。1. You must have seen the film Titanic.2. He must have been to Shanghai.
4)should +不定式完成式(have done)用于肯定句中，表示对过去行为的推测。He should have finished the work by now。表示“本应该做而实际上没有做某事”，其否定式表示某种行为本不该发生却发生了。可以与ought to +不定式完成式(have don e)互换。1. You ought to / should have helped him. (but you didn’t.)2. She shouldn’t have taken away my measuring tape, for I wanted to use it.
5) needn’t +不定式完成式(have done)表示“本来不必做而实际上做了某事”。You needn’t have watered the flowers, for it is going to rain.
6) will +不定式完成式(have done)主要用于第二、三人称，表示对已完成的动作或事态的推测。He will have arrived by now.

情态动词表示猜测肯定：must>should>could>may>might否定：can’t>shouldn’t>couldn’t>may not>表示要求，命令时，语气由 should(应该)、had better最好)、must(必须)渐强。必须掌握情态动词表示推测语气时的反意疑问句。例如：The road is wet. It must have rained, hasn t it?The road is wet. It must have rained last night, didn t it? (多了过去时的时间状语)I met him on his way home. He can’t be in the library now, isn t he?The coat is too close to the fire. It might get burnt, doesn t it?