高中英语情态动词的用法 学案
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高中英语情态动词的用法
can和could
情态动词
用法
例句
can/could
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.
在肯定句中，表示客观可能性，并不涉及具体某事会发生，常用来说明人或事物的特征（译为“有时会”）。要表达具体某事实际发生的可能性时，不用can，需用could，may，might。
As a human being, anyone can make a mistake.
I’m confident that a solution can be found.
He can be very forgetful sometimes.
I may stay at home this weekend.（实际可能性）
Peter might come to join us.(实际可能性)
It will be sunny in the daytime ,but it could rain tonight.(实际可能性)
表示请求和允许。表示请求，口语中常用could代替can，使语气更委婉。
Can we turn the air conditioner on?
Any police officer can insist on seeing a driver’s license.
In soccer, you can’t touch the ball with your hands.
Could you have her call me back when she gets home, please?
I wonder if I could just ask you to sign this.
表示对现在的动作或状态进行主观的猜测，主要用在否定句和疑问句中。
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?
表示惊异、怀疑、不相信等态度，主要用在否定句、疑问句和感叹句中。
Can this be an excuse for not giving them help?
This can’t be true.
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)
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
（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。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.
惯用形式“cannot …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“cannot but+ 不定式（不带to）”表示“不得不，只好”。如：
I cannot but admire her determination.我不得不钦佩你的决心。
二．may和 might
情态动词
用法
例句
may/might
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。
May I come in and wait?
——May I smoke here?
——No, you mustn’t(或No, you’d better not.)
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，在口气上比较客气，在日常用语中，用Can I征询对方意见更为常见。
Might I borrow your pen?
I wonder if I might speak to your son.
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。
It may rain this afternoon.
She might come to join us this afternoon.
I suppose he might have missed the train.
may用于祈使句表示祝愿
May you succeed.
May you live happily!
May she rest in peace.愿她安息。
惯用句式：
“may as well或might(just)as well+动词原形”意为“最好，满可以，倒不如”，相当于“had better或there is no reason to do anything else.
There is nothing to do, so I may as well go to bed.
You may as well tell us now, we’ll find out sooner or later.
I suppose we might as well go home.
And if you have to plough the field anyway, you might as well plant it at the same time.
三．must和have to
情态动词
用法
例句
must
表示“必须，应该”之意，语气比should，ought to强烈。其否定形式mustn’t表示“不准，不应该，禁止”等意
You must come to school on time.
Everybody must obey the law.
You mustn’t drive so fast in the street.
We mustn’t waste any more time.
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
1．—Must I come back before ten?
—Yes，you must.
----No, you needn’t(No, you don’t have to)
表示有把握的推测，意为“一定、准是、相必”，只
用于肯定句中
It must be my mother.
You must be hungry after a walk.
There must be a hole in the wall.
have to
“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。
The film is not interesting. I really must go now.
I have to go now, because my mother is in hospital.
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。
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 .
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。
You mustn’t go there.
You don’t have to go there.
注意：表示”偏要，硬要做某事
-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)
四．shall和should
情态动词
用法
例句
shall
用于第一、三人称构成的疑问句，表示征求对方意见或请求指示,其意为“要不要”、“…好吗”：
Shall I open the window?
Shall we say 6 o’clock, then?
Shall he come to see you?
1 用于第二、三人称陈述句中，表示说话人给对方的命令、警告、允诺、威胁、命令、规定、必然性等
2表示强制，用于法令、条约、规章中，意为“必须，应该”。
Don’t worry, you shall get the answer this afternoon.(允诺)
He shall be sorry for it one day, I tell you. （警告）
You shall do as I say. (命令)
If you children don’t do as I tell you, you shall not go to the party. (威胁)
The Persons under 18 shall not be employed in night work．不满十八岁的人不得雇佣干夜间工作。(表规定)
That day shall come(表必然性)
Candidates shall remain in their seats until all the papers have been collected. 试卷完全收回后，应试人才能离开座位。
should
表示劝告或建议，意为“应该”
What should I do?
Should I trust him?
You should read his new book.
表示推测，用在肯定句中，对现在的情况或可能发生的事的主观推测或期待。意为“想必，大概，或许” 。
【注】should表示推断时，语气较肯定，通常是指非常可能的事(因为暗示有一定的事实依据或合乎常理)，而may, might, could等表示推测时，则语气较不肯定，尤其是might, could。
It should be a nice day tomorrow.
It ‘s nearly 7 o’clock .Jack should speak in such a way.
He should be around sixty years old.
还可以用在if引导的条件句中，表示一件事听起来可能性很小，但也不是完全不可能，相当于“万一”的意思。从句谓语用should+动词原形构成，主句都一定用虚拟语气
Ask Tom to ring me up if you should see him. (你万一见到汤姆，请让他给我打个电话)
Should I be free tomorrow, I’ll come. (万一我明天有时间，我就过来)
If things should change suddenly, please let me know. (万一情况突变，请通知我)
1should表示意外或惊讶
2用于疑问句或感叹句中，表示意外、惊异的情绪，意为“竟会”，与why，what，how，who连用，如果是疑问句，则不需要回答。
It’s strange that he should come so late. 他竟然来这么迟真是奇怪。
I’m sorry that this should have happened. 我很遗憾竟然发生这种事。
I’m surprised that he should say so. 他竟这样说，这使我很惊讶。
Why should anyone want to marry Tony?
Don’t ask me. How should I know?
五．will和would
情态动词
用法
例句
will/would
用于表示意志或意愿或决心。will指现在，would指过去。
He is the man who will go his own way. (他首歌自行其是的人。)
They said they would meet us at 10:30 at the station.
表示请求、建议等和you连用，用would比用will委婉、客气。
Will you please take a message for him?
Would you please tell me your telephone number?
表示习惯或倾向，意为“总是，惯于”。will至现在，would指过去。
Fish will die without water.
People will talk. (人们总会说闲话。)
When we worked in the same office, we would often have coffee together.
表示推测，意为“很可能，大概”。will表示推测比should把握大，比must把握小。
These things will happen.
That will be the messenger ringing.
It would be about ten o’clock when he left home.
表示功能，意为“能，行”。惯用形式：will do/would do表示“解决问题”、“就行”。
That will be all right.
Either pen will do.
It would not do to work too late.（工作太晚不行。）
用于否定句中，意为“不肯”、“不乐意”
1．I won’t listen to your nonsense.
2．No matter what I said, he wouldn’t listen to me.
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.
六．need和dare
情态动词
用法
例句
need
用于表示“需要，必要”之意。做情态动词时，仅用于否定句和疑问句，只有现在时，过去式要用needn't have，疑问式用need+人称?,否定式用need not(即needn't），
1．—Need we leave soon?
—Yes, you must.(No, you needn't, or don’t have to)
2．You needn't have hurried.
(=It was not necessary for you to hurry，but you did).你当时不必这么匆忙。
做实义动词时，其变化与一般的实义动词相同，后接带to的不定式（need doing = need to be done ）,过去式用needed、did you need?和didn't need,肯定式用needs/needed/need,疑问式用do、does、did提问，否定式要在前面加don't、doesn't、didn't
1. A job like nursing needs patience and understanding.(need+名词，need understanding=need to be understood,需要被理解)
2．He needs to see a doctor.(need to do)
3．Do you still need volunteers to help clean up after the party?(need somebody to do something)
4．They didn't need to start so early.(do not need to do)
dare
用于表示“敢于”之意。做情态动词，没有人称和数的变化，主要用于否定句、疑问句和条件状语从句中
1．—Dare you tell her the truth?
—Yes, I dare. /No, I daren’t.
How dare you accuse me of lying!
He daren’t admit this.
用作实义动词时，其变化与一般的实义动词相同。在肯定句中，dare后接带to的不定式；否定句中，dare后既可接带to的不定式，也可接不带to的不定式。
Only a few journalists dared to cover the story.
He doesn’t dare (to) go there alone.
Don’t you dare (to) touch it?
七．ought的用法：
情态动词
用法
例句
ought to do
表示“应该”之意
You ought to take care of him.
—Ought I go now?
—Yes, you ought to. /No, you oughtn’t to.
表示推测。注意与must表示推测是的区别
He must be home by now. (断定他已到家)
He ought to be home by now. (不十分肯定)
This is where the oil must be. (比较直率)
This is where the oil ought to be. (比较含蓄)
说明：should与ought to 表示“应该”时的区别
should 表示自己的主观看法，而ought to的语气中，含有“按道理应该……”之意。若要反映客观情况或涉及法律义务和规定，一般用ought to。如：
You should help them with their work.
You are his father. You ought to get him to receive good education.
八．“情态动词+have done”用法
情态动词+have done
用法
例句
must have done
表示主观上对过去已经发生的行为进行推测，意为“想必，准是，一定做了某事”
She must have gone through a lot.
He must have visited the White House during his stay in the United States.
may/might have done
表示对过去已发生行为的推测，意为“也许/或许已经（没有）……“。一般用于肯定句或否定句中，不用于疑问句。用might则表示语气更加不肯定。
You may have learnt the news.
He may not have heard his name called.
Sorry I’m late. I might have turned off the alarm clock and gone back to sleep again.
can…have done
cannot have done
表示对过去发生的行为的怀疑和不肯定，通常用在否定句和疑问句中。（can换成could时语气委婉）
Where can she have gone?
Could he have done such a foolish thing?
The boy can’t have finished reading the book so soon because it is difficult even to an adult.
could have done
可用于肯定句中，表示“可能已经……”之意，此外，还可以表示过去能做而没做的事，有一种对过去为付诸实施的事情的惋惜。
He could have killed himself driving at a dangerous speed.
You could have been more considerate.
You could have done better, but you were too careless.
might have done
表示“本来可能……，但实际上没有发生的事情”。另外，还可以表示“本来应该或可以做某事”之意，含有轻微的责备语气。
You should not swim in that sea. You might have been eaten by a shark.
He might have given him more help, thought he was busy.
should/ought to have done
用于肯定句时，表示本该做某事，而实际上未做；用于否定句时，则表示不该做的事反而做了。
He should have known that the police would never allow this sort of thing.
You shouldn’t have done it so carelessly.
You ought to have returned the book earlier.
You ought not to have refused his offer.
needn’t have done
表示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”
You needn’t have watered the plants, for it is going to rain.
I didn’t need to buy the dictionary. I had a copy at home.
had better have done
用于事后的建议，含轻微责备的口吻，意为“当时最好做了某事”，其否定式had better not have done表示相反的含义。
You had better have started earlier.
You had better not have scolded her.
would rather have done
表示“当时宁愿做了某事”，其否定式would rather not have done表示相反的含义，两者都表示“后悔”之意。
1．I would rather have taken his advice.
2．I would rather not have told him the truth.
can和could
情态动词
用法
例句
can/could
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.
在肯定句中，表示客观可能性，并不涉及具体某事会发生，常用来说明人或事物的特征（译为“有时会”）。要表达具体某事实际发生的可能性时，不用can，需用could，may，might。
As a human being, anyone can make a mistake.
I’m confident that a solution can be found.
He can be very forgetful sometimes.
I may stay at home this weekend.（实际可能性）
Peter might come to join us.(实际可能性)
It will be sunny in the daytime ,but it could rain tonight.(实际可能性)
表示请求和允许。表示请求，口语中常用could代替can，使语气更委婉。
Can we turn the air conditioner on?
Any police officer can insist on seeing a driver’s license.
In soccer, you can’t touch the ball with your hands.
Could you have her call me back when she gets home, please?
I wonder if I could just ask you to sign this.
表示对现在的动作或状态进行主观的猜测，主要用在否定句和疑问句中。
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?
表示惊异、怀疑、不相信等态度，主要用在否定句、疑问句和感叹句中。
Can this be an excuse for not giving them help?
This can’t be true.
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)
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
（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。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.
惯用形式“cannot …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“cannot but+ 不定式（不带to）”表示“不得不，只好”。如：
I cannot but admire her determination.我不得不钦佩你的决心。
二．may和 might
情态动词
用法
例句
may/might
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。
May I come in and wait?
——May I smoke here?
——No, you mustn’t(或No, you’d better not.)
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，在口气上比较客气，在日常用语中，用Can I征询对方意见更为常见。
Might I borrow your pen?
I wonder if I might speak to your son.
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。
It may rain this afternoon.
She might come to join us this afternoon.
I suppose he might have missed the train.
may用于祈使句表示祝愿
May you succeed.
May you live happily!
May she rest in peace.愿她安息。
惯用句式：
“may as well或might(just)as well+动词原形”意为“最好，满可以，倒不如”，相当于“had better或there is no reason to do anything else.
There is nothing to do, so I may as well go to bed.
You may as well tell us now, we’ll find out sooner or later.
I suppose we might as well go home.
And if you have to plough the field anyway, you might as well plant it at the same time.
三．must和have to
情态动词
用法
例句
must
表示“必须，应该”之意，语气比should，ought to强烈。其否定形式mustn’t表示“不准，不应该，禁止”等意
You must come to school on time.
Everybody must obey the law.
You mustn’t drive so fast in the street.
We mustn’t waste any more time.
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
1．—Must I come back before ten?
—Yes，you must.
----No, you needn’t(No, you don’t have to)
表示有把握的推测，意为“一定、准是、相必”，只
用于肯定句中
It must be my mother.
You must be hungry after a walk.
There must be a hole in the wall.
have to
“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。
The film is not interesting. I really must go now.
I have to go now, because my mother is in hospital.
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。
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 .
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。
You mustn’t go there.
You don’t have to go there.
注意：表示”偏要，硬要做某事
-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)
四．shall和should
情态动词
用法
例句
shall
用于第一、三人称构成的疑问句，表示征求对方意见或请求指示,其意为“要不要”、“…好吗”：
Shall I open the window?
Shall we say 6 o’clock, then?
Shall he come to see you?
1 用于第二、三人称陈述句中，表示说话人给对方的命令、警告、允诺、威胁、命令、规定、必然性等
2表示强制，用于法令、条约、规章中，意为“必须，应该”。
Don’t worry, you shall get the answer this afternoon.(允诺)
He shall be sorry for it one day, I tell you. （警告）
You shall do as I say. (命令)
If you children don’t do as I tell you, you shall not go to the party. (威胁)
The Persons under 18 shall not be employed in night work．不满十八岁的人不得雇佣干夜间工作。(表规定)
That day shall come(表必然性)
Candidates shall remain in their seats until all the papers have been collected. 试卷完全收回后，应试人才能离开座位。
should
表示劝告或建议，意为“应该”
What should I do?
Should I trust him?
You should read his new book.
表示推测，用在肯定句中，对现在的情况或可能发生的事的主观推测或期待。意为“想必，大概，或许” 。
【注】should表示推断时，语气较肯定，通常是指非常可能的事(因为暗示有一定的事实依据或合乎常理)，而may, might, could等表示推测时，则语气较不肯定，尤其是might, could。
It should be a nice day tomorrow.
It ‘s nearly 7 o’clock .Jack should speak in such a way.
He should be around sixty years old.
还可以用在if引导的条件句中，表示一件事听起来可能性很小，但也不是完全不可能，相当于“万一”的意思。从句谓语用should+动词原形构成，主句都一定用虚拟语气
Ask Tom to ring me up if you should see him. (你万一见到汤姆，请让他给我打个电话)
Should I be free tomorrow, I’ll come. (万一我明天有时间，我就过来)
If things should change suddenly, please let me know. (万一情况突变，请通知我)
1should表示意外或惊讶
2用于疑问句或感叹句中，表示意外、惊异的情绪，意为“竟会”，与why，what，how，who连用，如果是疑问句，则不需要回答。
It’s strange that he should come so late. 他竟然来这么迟真是奇怪。
I’m sorry that this should have happened. 我很遗憾竟然发生这种事。
I’m surprised that he should say so. 他竟这样说，这使我很惊讶。
Why should anyone want to marry Tony?
Don’t ask me. How should I know?
五．will和would
情态动词
用法
例句
will/would
用于表示意志或意愿或决心。will指现在，would指过去。
He is the man who will go his own way. (他首歌自行其是的人。)
They said they would meet us at 10:30 at the station.
表示请求、建议等和you连用，用would比用will委婉、客气。
Will you please take a message for him?
Would you please tell me your telephone number?
表示习惯或倾向，意为“总是，惯于”。will至现在，would指过去。
Fish will die without water.
People will talk. (人们总会说闲话。)
When we worked in the same office, we would often have coffee together.
表示推测，意为“很可能，大概”。will表示推测比should把握大，比must把握小。
These things will happen.
That will be the messenger ringing.
It would be about ten o’clock when he left home.
表示功能，意为“能，行”。惯用形式：will do/would do表示“解决问题”、“就行”。
That will be all right.
Either pen will do.
It would not do to work too late.（工作太晚不行。）
用于否定句中，意为“不肯”、“不乐意”
1．I won’t listen to your nonsense.
2．No matter what I said, he wouldn’t listen to me.
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.
六．need和dare
情态动词
用法
例句
need
用于表示“需要，必要”之意。做情态动词时，仅用于否定句和疑问句，只有现在时，过去式要用needn't have，疑问式用need+人称?,否定式用need not(即needn't），
1．—Need we leave soon?
—Yes, you must.(No, you needn't, or don’t have to)
2．You needn't have hurried.
(=It was not necessary for you to hurry，but you did).你当时不必这么匆忙。
做实义动词时，其变化与一般的实义动词相同，后接带to的不定式（need doing = need to be done ）,过去式用needed、did you need?和didn't need,肯定式用needs/needed/need,疑问式用do、does、did提问，否定式要在前面加don't、doesn't、didn't
1. A job like nursing needs patience and understanding.(need+名词，need understanding=need to be understood,需要被理解)
2．He needs to see a doctor.(need to do)
3．Do you still need volunteers to help clean up after the party?(need somebody to do something)
4．They didn't need to start so early.(do not need to do)
dare
用于表示“敢于”之意。做情态动词，没有人称和数的变化，主要用于否定句、疑问句和条件状语从句中
1．—Dare you tell her the truth?
—Yes, I dare. /No, I daren’t.
How dare you accuse me of lying!
He daren’t admit this.
用作实义动词时，其变化与一般的实义动词相同。在肯定句中，dare后接带to的不定式；否定句中，dare后既可接带to的不定式，也可接不带to的不定式。
Only a few journalists dared to cover the story.
He doesn’t dare (to) go there alone.
Don’t you dare (to) touch it?
七．ought的用法：
情态动词
用法
例句
ought to do
表示“应该”之意
You ought to take care of him.
—Ought I go now?
—Yes, you ought to. /No, you oughtn’t to.
表示推测。注意与must表示推测是的区别
He must be home by now. (断定他已到家)
He ought to be home by now. (不十分肯定)
This is where the oil must be. (比较直率)
This is where the oil ought to be. (比较含蓄)
说明：should与ought to 表示“应该”时的区别
should 表示自己的主观看法，而ought to的语气中，含有“按道理应该……”之意。若要反映客观情况或涉及法律义务和规定，一般用ought to。如：
You should help them with their work.
You are his father. You ought to get him to receive good education.
八．“情态动词+have done”用法
情态动词+have done
用法
例句
must have done
表示主观上对过去已经发生的行为进行推测，意为“想必，准是，一定做了某事”
She must have gone through a lot.
He must have visited the White House during his stay in the United States.
may/might have done
表示对过去已发生行为的推测，意为“也许/或许已经（没有）……“。一般用于肯定句或否定句中，不用于疑问句。用might则表示语气更加不肯定。
You may have learnt the news.
He may not have heard his name called.
Sorry I’m late. I might have turned off the alarm clock and gone back to sleep again.
can…have done
cannot have done
表示对过去发生的行为的怀疑和不肯定，通常用在否定句和疑问句中。（can换成could时语气委婉）
Where can she have gone?
Could he have done such a foolish thing?
The boy can’t have finished reading the book so soon because it is difficult even to an adult.
could have done
可用于肯定句中，表示“可能已经……”之意，此外，还可以表示过去能做而没做的事，有一种对过去为付诸实施的事情的惋惜。
He could have killed himself driving at a dangerous speed.
You could have been more considerate.
You could have done better, but you were too careless.
might have done
表示“本来可能……，但实际上没有发生的事情”。另外，还可以表示“本来应该或可以做某事”之意，含有轻微的责备语气。
You should not swim in that sea. You might have been eaten by a shark.
He might have given him more help, thought he was busy.
should/ought to have done
用于肯定句时，表示本该做某事，而实际上未做；用于否定句时，则表示不该做的事反而做了。
He should have known that the police would never allow this sort of thing.
You shouldn’t have done it so carelessly.
You ought to have returned the book earlier.
You ought not to have refused his offer.
needn’t have done
表示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”
You needn’t have watered the plants, for it is going to rain.
I didn’t need to buy the dictionary. I had a copy at home.
had better have done
用于事后的建议，含轻微责备的口吻，意为“当时最好做了某事”，其否定式had better not have done表示相反的含义。
You had better have started earlier.
You had better not have scolded her.
would rather have done
表示“当时宁愿做了某事”，其否定式would rather not have done表示相反的含义，两者都表示“后悔”之意。
1．I would rather have taken his advice.
2．I would rather not have told him the truth.