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情 态 动 词
情态动词是一种本身有一定的词义，但要与动词原形及其被动语态一起使用，给谓语动词增添情态色彩，表示说话人对有关行为或事物的态度和看法，认为其可能、应该或必要等。情态动词后面加动词原形。
什么是情态动词？
情态动词的语法特征
1. 没有人称和数的变化，即情态动词第三人称单数不加-s。
2. 不能独立使用，它和后面的动词构成谓语。
3. 情态动词除ought 和have 外，后面只能接动词原形。
4. 情态动词没有非谓语形式，即没有不定式、分词等形式。
5. 个别情态动词有现在式和过去式两种形式，过去式可以用来表达更加客气、委婉的语气，时态性不强，可用于过去，现在或将来。
常见情态动词： can/could, may/might, ought to, must, need, dare, shall/should, will/would, have to, used to
情态动词 否定式 疑问式与简答
can can not / cannot /can’t do Can…do… Yes,…can.No,…can’t.
could couldn’t do may may not do May…do… Yes,…may.No,…mustn’t/can’t.
might might not do Might…do… Yes,…mightNo,…might not.
must must not/mustn’t do Must…do… Yes,…must.No,…needn’t/don’t have to.
have to don’t have to do Do…have to do… Yes,…do. No,…don’t.
ought to ought not to/oughtn’t to do Ought…to do… Yes,…ought. No,…oughtn’t.
shall shall not/shan’t do Shall…do… Yes,…shall. No,…shan’t.
should should not/shouldn’t do Should…do…
will will not/won’t do Will…do… Yes,…will. No,…won’t.
would would not/wouldn’t do dare dare not/daren’t do Dare…do… Yes,…dare. No,…daren’t.
need need not/needn’t do Need…do… Yes,…must. No,…needn’t.
used to used not/usedn’t/usen’t to dodidn’t use to do Used…to do… Yes,…used. No,…use(d)n’t.Did…use to do… Yes,…did. No,…didn’t.
情态动词 否定式 疑问式与简答
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 e 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!
初中情态动词基础用法
can could 1. 表示体力或者脑力（知识，技能）所产生的能力 He could read books when he was only 6 years old.
2.表示请求，建议，用could比can更委婉客气 Can you wait for me for a while
3. 表示允许，许可，用could比can更委婉客气 Can I borrow your bike to fetch my belongings
may might 1. 表示允许，请求，might 比may 语气更委婉 May I ask some questions about the accident
must 1. 表示“必须”，强调主观看法，只有现在时形式 Everyone must obey the rules.
2. mustn't 表示“禁止，不准” You mustn't speak to your mother like that.
have to 表示“必须，不得不”，着重强调客观需要，可用于过去时和将来时 Because of the virus, we have to study online.
will would 1. 用于各种人称，表示意志或决心。will指现在，would指过去。 I will try my best to catch up with others.
2. 用于第二人称的疑问句中表示礼貌的询问或请求，would比will更委婉 Would you help me to deal with the problem
used to 表示过去经常性或习惯性的动作或状态，现在已经结束 He used to take exercises everyday in the morning.
shall should shall 表示征询意见，用于第一第三人称疑问句 Shall I get you some tea
should表义务，意为“应该”，用于各种人称 You should be polite to the old.
ought to 表示从法律上或从道义上“应该”，语气比should重 Every parent ought to send their children to school when they reach 7 years old.
need 表示“需要，必须”，通常用于否定，疑问句中，且只有现在时 You needn't worry about the virus too much now.
dare 表示“敢于”，用于否定，疑问句中 He dare not go there alone.
need dare
情态动词 否定句: needn't do sth 疑问句: Need......do.... 否定句: dare not do sth
疑问句: Dare....do....
实义动词 肯定句: need to do sth 否定句: don't need to do sth 疑问句: Do....need.... 肯定句: dare to do sth
否定句: don't dare (to) do sth
疑问句: Do......dare......
needn't do sth= don't need to do sth dare not do sth=don't dare (to)do sth
高中阶段情态动词的其它用法
can could 1. 否定句，疑问句和感叹句中，表示怀疑，惊异，不相信的态度 That can't be true!
2. can't ....too much\enough 意为“再怎么也不过分” I can't thank you too much!
3. cannot but＋do sth.表示“不得不，只好” He can't but choose to go.
may might 1. 表示祝愿（不用might）,采用部分倒装语序：may+主语+动词原形+其它成分！ May you be happy!
2.may\might as well do sth, 意为“做某事也无妨，倒不如做某事” There is so much time left. We may as well watch a movie to kill time.
must 有“偏要，硬要”之意 If you must know my idea, I have to tell you that I don't agree with you.
will would 1. 表示习惯性，经常性，倾向性，意为“总是，惯于”，will指现在，would指过去 He would spend at least one hour reading everyday.
2.表示功能，意为“能”或“行” I tried many times, but the door would not open.
shall should 1. shall表示说话人的意愿，有命令，允许，警告，决心等意思，用于第二，第三人称 You shall do as I have told you to .
2. shall用在条约，规章，法令等文件中，表示必然结果，意为“必须”，比must语气强 You shall maintain your parents when they are old.
3. should用于表示惊奇，遗憾不该发生的事情，意为“居然，竟然” He should kill all of his family members.
4.should用在虚拟语气中， The doctor suggested that you should quit smoking.
现在
肯定 must>should（ought to）>can >could>may>might
否定 can't>couldn't>maynnot>mightn't
疑问 can, could
情态动词表推测
表示对目前或将来情况的推测往往用“情态动词＋动词原形”这种结构。
1．must表示推测时只能用于肯定句中，意为“一定，必定”，表示十分肯定的语气(在疑问句中或否定句中要用can)。
He must be ill.He looks so pale.
It's the office！So you must know eating is not allowed here.
2. should用来表示推测时意为“应该”，即含有“按道理来说应当如此”的意思。
There shouldn't be any difficulty about passing the road test since you have practiced a lot in the driving school.
因为你在驾校训练了那么多，通过路考应该没什么困难。
3．can用于肯定句中表示可能性，意为“有时会”；用于疑问句中可以表示推测，意为“可能”，有时表示一种惊讶的语气；用于否定句中也可以表示推测，can't意为“不可能”，语气很强烈。
It is usually warm in my hometown in March，but it can be rather cold sometimes.
Mr.Bush is on time for everything.How can it be that he was late for the meeting
He can't be in the classroom，for the light has been turned off.
4．may用于肯定句中可以用来表示推测，意为“可能”；用于否定句中也可以表示推测，may not意为“可能不”，表示一种不太确定的语气。may在疑问句中一般不表示推测。
Some people who don't like to talk much are not necessarily shy；they may just be quiet people.
言语不多的人未必就是害羞。他们或许就是安静的人。
5. 表示对现在正在发生的事情进行推测要用“情态动词＋be＋现在分词”这种结构。
My mother must be watering the flowers in the garden now.
The students may be climbing the mountain at the moment.
6. would, could, should, might 并不一定与过去的时间有关，而是表示可能性弱于他们相应的现在形式。如：
This may / might be done by him. （语气依次递减）
过去
肯定 must have done>may have done>might have done
否定 can't have done>couldn't have done>maynot have done>mightn't have done
疑问 can have done, could have done
构成 用法 举例
must＋ have done 表示对过去发生的事情十分肯定的推测。must表示推测时，不能用于否定句和疑问句。无mustn't have done这个结构。 The man must have stayed up for he looks so sleepy.
构成 用法 举例
may/might ＋have done 用于肯定句和否定句，表示对过去发生某事的可能性的推测，意思为“或许(已经)……”“或许还没有……”。 ①He said that she might have missed the plane.
②He may not have gone home; he might have gone somewhere else.
构成 用法 举例
can/could＋ have done 多用于否定句和疑问句，表示对过去某事发生的可能性的否定或质疑，意思为“不可能(已经)……了”，“可能(已经)……了吗？” He can't/couldn't have seen her there.
Can any of you have remembered all the vocabulary in high school
could(不用can)+have done,在肯定句中表示“本来能够…而没能…”，具有婉转的批评和责备之意。
You could have told me earlier.
你本该早点告诉我的。
情态动词表虚拟
should/ought to+have done用于肯定句时，表示“本该做某事而实际上没做”，用于否定句时，则表示“不该做的事反而做了”。
You should have told him a week ago.
你本来应该在一周前告诉他的。
might（不用may）+have done表示“本来可能…”，但实际上没有发生的事。另外，还可表示“本来应该或可以做某事”之意，含有轻微的责备语气。
1.You might not have told her.
你本可以不告诉他的。（事实上你告诉他了）
2. You might have come earlier.
你本可以早点来的。（但没有这样）
needn’t +have done 表示做了本来不必去做的事。
1.She needn’t have gone to the station yesterday.
昨天她本不必到火车站去的.（昨天她去了）
2.You needn’t have bought it.
你本可不必买它的。 （你买了）
综述
情态动词+完成式 意义
must have done 用于对过去的事情作出肯定的推测，意为“想必/准是/一定做了某事”，无mustn't have done这个结构。
can/could have done 1.用于表虚拟，意为“本来能够....... （而实际没做）”
2.用于表推测，多用于疑问句中，意为“过去可能会......”
can/could not have done 1用于表虚拟，意为“过去不可能......（而实际却做了） ”
2.用于表推测，意为“过去没能......”
may/might have done 用于表推测，意为“也许/或许已经...... ”一般只用于肯定句和否定句中（在否定句中表示 可能不 ），不用于疑问句。用might则表示语气更加不肯定。
might have done 用于表虚拟，意为“本来可能…”，但实际上没有发生的事。
should/ought to have done 用于表虚拟，意为“本该做某事而实际上未做”。
shouldn't/ought not to have done 用于表虚拟，意为“本不该做而做了某事”。
needn't have done 用于表虚拟，意为“做了本来不必去做的事 ”。
注意：didn't need to do 表示 没必要做而实际上也没有做某事
情态动词表虚拟其它用法
had better have done 用于表虚拟，含轻微责备的口气，意为“要是当时做了某事就好了”，
其否定式 had better not have done 表达相反的含义
would rather have done 用于表虚拟，意为 “ 宁愿当时做某事”，
其否定式would rather not have done 表达相反的含义，两者都表示 后悔 之意。
would like /love to have done 用于表虚拟，表示过去愿意做某事，但未做成

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