情态动词表示说话人对动作或状态的各种观点和态度，如需要、猜测、意愿或怀疑等。情态动词有词义，但不完全，是所谓的“辅助性”动词，在句中不能单独充当谓语。
A.情态动词的各种形式见下表：
情态动词
may
might
can
could
must
have to
ought to
will
would
shall
should
need
dare
used to
否定式
may not
might not
cannotcan not
could not
must not
do not have to
ought not to
will not
would not
shall not
should not
need not
dare not
used not to
did not use to
简略否定式
mayn't（老式英语，现在不常见）
mightn't
can't
couldn't
mustn't
don't have to
oughtn't to（否定句中to可省略）
won't
wouldn't
shan't（只用于英国英语）
shouldn't
needn't
daren't
usedn't to
didn't use to
B．情态动词除ought to, used to等外，后面只接不带to的不定式。
1．情态动词+do
You shouldn't be so careless.你不该这样粗心大意。
Jessica told him yesterday she might not go on the trip.
杰西卡昨天告诉他，她可能不去旅行了。
Difficulties can and must be overcome.
困难能够而且必须克服。
2．情态动词+be doing
She must be listening to pop music.
她肯定在听流行音乐。
You should be reviewing your lessons.
你应该在复习功课。
My mother maymight be cooking now.
我妈妈可能正在做饭。
3．情态动词+have done
They might have visited the Great Wall.
他们可能参观过长城了。
He must have got up very early to catch the train.
他一定起得很早去赶火车了。
You ought to have come earlier.
你本该早一点儿来。
4．情态动词+be done
This word can also be used as a verb.
这个词也可以用作动词。
Something must be done to stop pollution.
必须采取措施来制止污染。
The work ought to have been finished long ago.
这工作早就该完成了。
C.情态动词第三人称单数一般现在时没有词形变化。
You ought to wear a raincoat.
你应该穿件雨衣。
She ought to wear a raincoat.
她应该穿件雨衣。
Plants must have oxygen in order to live.
为了存活植物必须有氧气。
A plant must have oxygen in order to live.
为了存活植物必须有氧气。
D.情态动词的时态并不是区分时间的主要标志。在一些场合中，情态动词的现在式和过去式都可以表示现在时间、过去时间或将来时间。
I'm afraid it might rain tonight.
我看今晚可能要下雨。
Could I borrow your thermos
我可以借用你的暖水瓶吗？
It's a nice day today. We could go for a walk.
今天天气不错，我们可以出去散散步。
E.情态动词是互相排斥的，一般不允许两个意义相近的情态动词连用。
【误】Soldiers must have to obey orders.
【正】Soldiers have to obey orders.
军人必须服从命令。
【正】Soldiers must obey orders.
军人必须服从命令。
【误】Can I be able to borrow two books at a time
【正】Can I borrow two books at a time
我能一次借两本书吗？
【正】Will I be able to borrow two books at a time
我能一次借两本书吗？
A. may和might
1．表示请求、许可，常译为“可以”。
在口语中可用can, could代替may，但在正式场合用may。表示允许时，也可用might代替，might不表示过去时，而是表示口气比较婉转。
You may take this seat if you like.
如果你喜欢可以坐这个位置。
MayCan Could Might I have a talk with you
我可以和你谈谈吗？
--- MayMight I come into the room to see my mother
我可以进房间看我母亲吗？
--- No, you mustn't. She needs to have a good rest.
不，你不能进。她需要好好休息。
提示：
May I ...问句常见的肯定回答和否定回答。
肯定回答
Yes, please.
Certainly.
Yes, of course.
Sure.
Go ahead, please.
否定回答
No, you can't.（最常见）
No, you mustn't.（具有强烈禁止的意思）
Please don't. You'd better not.
I don't think you can.
I'm sorry it's not allowed.
2．表示推测，可译为“可能，也许”。
Your math teacher maymight be in his office. 你们的数学老师可能在办公室里。（一般情况下，might表示的可能性很小）
The light isn't on. It maymight be broken.
那盏灯没有亮，它可能坏了。
There may might be some ink left in the bottle.
瓶子里也许还剩点儿墨水。
注意：
用may表示推测一般不用于疑问句，在疑问句中通常用can来代替。
Can he be at home
他可能在家吗？
--- Can it be true
这可能是真的吗？
--- It may be, or may not be.
可能是，也可能不是。
3．用在目的状语从句中，构成谓语。
He wants to take a taxi so that he may get there in time.
他想坐出租车，这样他就能及时到达那里。
I arrived at the airport earlier in order that I might meet him.
我早早地就到了机场为了能接到他。
4．有时可以用于祈使句表示祝愿。
May you succeed.
祝你成功
May you be happy.
祝你快乐。
May that day come soon.
希望这一天早日到来。
B. can和could
1．表示能力，可译为“能，会”。
I can swim.我会游泳。
Emily can dance well and her mother could dance well when she was young.
艾米丽舞跳得很好，她妈妈年轻时舞跳得也很好。
The cinema can seat 1,000 people.
这电影院能容纳1，000人。
I could not read such an easy book when I was 7 years old.
我七岁时连如此简单的书我也看不懂。
2．表示允许、许可，常用在口语中。could比can语气上要客气。
--- Could I use your dictionary
我可以用一下你的字典吗？
---Yes, go ahead.
可以，用吧。（或Yes, you can.但不能说Yes, you could.）
Could Can you tell me how to get to the zoo
劳驾，你能告诉我怎么去动物园吗？
He asked me whether he could take the book out of the reading room.
他问我可不可以把书带出阅览室。
3．表示推测，可用于肯定句（can罕见）、否定句和疑问句，但更常见于疑问句或否定句。在此种用法中can和could没有时态的区别，只是表示可能性的大小，can表示推测的可能性比could大。
Can he be ill at home
他会是生病在家吗？
Can the story be true
这个故事会是真的吗？
He cannot be at home.
他不可能在家。
You mustn't smoke while you are walking around in the woods. You could start a fire.
在林子里走时一定不要吸烟，那样可能会引起火灾。
4．表示惊异、怀疑、不相信等态度，主要用于否定句和疑问句中。
How can you be so careless
你怎么这么粗心？
Where can could they have gone
他们会去了哪里？
He can'tcouldn't be over sixty.
他不可能超过60岁。
5．Could可以用在虚拟条件句中。
If I could fly, I should be very happy.
如果我能飞，我会很高兴。
If you had followed my advice, you could have finished it.
如果你当时听我的，你早就做完了。
If you had tried harder, you could have passed your exam.
如果你再努力些，你就能通过考试了。
６．can与be able to的区别
①can表示“能力”时，和be able to相当，许多场合都可以互相替换。但当叙述过去经过一番努力才能完成的事情或前面有特殊说明，表示你有能力时，只能用be able to。
【正】Can you speak any foreign languages
你会说外语吗？
【正】Are you able to speak any foreign languages
你会说外语吗？
【误】The fire spread the building quickly but everybody could escape.
【正】The fire spread the building quickly but everybody was able to escape.
大火迅速蔓延到整幢大楼，但大家都逃了出来。
【正】The fire spread the building quickly but everybody managed to escape.
大火迅速蔓延到整幢大楼，但大家都想法逃了出来。
②be able to比can有更多形式。
No one could answer the question.
没人能回答这个问题。（这里could可用was able to代替）
When he grows up, he will be able to support his family.
他长大后就能养家了。
Frank is ill. He hasn't been able to go to school for one week.
弗兰克病了，已经一周没去上学了。
I'm sorry for not being able to help you in time.
对不起，不能及时帮你的忙。
③could经常和动词see, hear, smell, taste, feel, remember, understand等连用。
When we went into the house, we could smell something burning.
当我们走进屋子时，我们闻到什么东西烧焦了。（不用was able to）
She spoke in a very low voice, but I could understand what she said.
虽然她讲话的声音很低，但我还是明白了她说的话。
④在谈论说话时发生的动作，用can，不用be able to。
【误】Look! I'm able to swim.
【正】Look! I can swim.
看，我会游泳了！
C．must和have to
1．must表示有做某一动作的必要或义务，强调主观看法，可译为“必须，应该”。
Everyone must obey the rule.
人人都必须遵守制度。
We must do everything step by step.
我们必须逐步做每件事。
Teachers must be patient enough with their students.
老师必须对学生有足够的耐心。
2．have to表示因客观需要促使主语不得不做某事。
You can't turn right here. You have to turn left.
你不能在这里右拐，你必须左拐。
My eyesight is very poor. I have to wear glasses for reading.
我的视力很差，看书时不得不戴眼镜。
You have to pass a test before you can get a driving licence.
你在取得驾照之前必须先通过考试。
提示：
在口语中，我们可以使用have got to来代替have to.
I've got to work on Sunday.
我不得不星期天工作。
When has Ann got to go
安必须什么时候走？
3．must与have to的比较。
must与have to在表示“必须”这个意思时意义相近，但在用法上有所区别。
①must含有说话者的强烈决意（表示主观的看法），have to则表示外力环境或习惯使然（即表示客观的必要，作“不得不”解）。
I must study hard.
我必须努力学习。（发自内心的决定）
I have to study hard.
我不得不努力学习。（外界因素逼迫）
You must stay for supper.
你必须留下来吃晚饭。（because I want you to）
You have to stay for supper.
你得留下来吃晚饭。（because there is nowhere else to go）
②must只有一种形式，而have to可有多种时态。
They had to put off the sports meet due to the bad weather.
由于坏天气，他们不得不推迟运动会。
These last two days he has had to take a rest at home.
这两天他必须一直在家休息。
③must的否定式和have to的否定式的意思完全不同。
You must keep it a secret. You mustn't tell anyone.
你必须保密，你不可以告诉任何人。（mustn't表示“禁止”）
You don't have to tell me the secret.你不必告诉我这个秘密。
（don't have to意思是“没有必要”= don't need to）
4．must用于表示推测，它的肯定程度比may, might, could大得多，一般只用于肯定句。
①must do (这里的do通常是状态动词或系动词)，表示对现在状态的推测。
He must be very lazy for his desk is very untidy.
他肯定很懒，因为他的课桌很不整洁。
Carol must get very bored with her job. She does the same thing every day.
卡罗尔肯定对她的工作厌烦了，她每天都做同样的事。
②must be doing表示对现在动作或状态的推测。
Put on more clothes. You must be feeling cold with only a shirt on.
多穿点儿衣服，你只穿一件衬衣，肯定觉得冷。
③must have done表示对过去的动作或状态的推测。
The ground is wet. It must have rained last night.
地面是湿的，昨晚肯定下雨了。
I didn't hear the phone. I must have been asleep.
我没听见电话铃响，我一定是睡着了。
提示：
must表示推测只用于肯定句，否定句和疑问句要用can, could来代替must。
He's just had his lunch. He can't be hungry already.
他刚吃过午饭，不会饿的。
They have just arrived here. They can't know many people.
他们刚到这里，不可能认识很多人。
Leslie walked past me without speaking. He can'tcouldn't have seen me.
莱斯利从我身边走过而没打招呼，他肯定没看见我。
5．must可用来表示根据逻辑推理必然要发生的事，可译为“必然会，总是会”。
We all must die.
我们都会死。
Truth must be out.
真相必然会大白的。
Winter must be followed by spring.
冬天到了，春天还会远吗？
6．must有时可用来表示“偏偏”的意思。
Why must it rain today
为什么偏偏在今天下雨？
When I was taking a nap, a student must knock at the door.
正当我午睡时，偏偏一个学生在这个时候来敲门。
D．will和would
1.will和would可用于第二人称疑问句，表示请求和建议等。would比will委婉客气。
Will you have some tea
你喝点茶，好吗？
Will you share your happiness with us
你可以把你的欢乐与我们共享吗？
Would you pass this book to the student in the last row
请你把这本书传给最后一排的学生好吗？
必背：
WillWould you ...表示请求和建议的答复。
肯定回答
Yes, please.是的，请。
Certainly.当然可以。
Sure.当然了。
All right.好啊！
否定回答
I'm sorry. I can't.对不起，不行。
No, thank you.不，不行。
No, I won't.不，不行。
2．will和would可表示意志、愿望和决心，用于各种人称陈述句。
I will do anything for you.
我愿为你做任何事。
I will never tell you the secret.
我永远不会告诉你这个秘密。
None is so blind as those who won't see.
不愿看的人眼睛最瞎。
They would not let him in because he was poorly dressed.
他们不让他进去因为他衣着破旧。
3．will和would可表示某种倾向或习惯性动作。will表示现在的习惯动作，would表示过去的习惯动作。
He will surf the Internet every night.
他每天晚上都在上网。
The boy will sit there hour after hour looking at the traffic go by.
那男孩常常坐在那儿好几个钟头，看着车辆行人通过。
He would be nervous when he met strangers.
遇见陌生人时他总是很紧张。
In class he would ask some silly questions, and his classmates would laugh at him.
课上，他总是问一些蠢问题，他的同学们总是嘲笑他。
4．will可表示固执坚持，这时will不可使用'll的简略形式。用于非人称主语时，表示物体的固有性质和倾向。
I will take the job, and no one can stop me.
我就要这个工作，没有人可阻止我。
He won't do what he's told.
他就是不愿按所吩咐的去做。
The window won't open.
窗子打不开。
This glass will not crack under heavy pressure.
这种玻璃在重压下也不会破碎。
5．will表示将来时间时，不可用于条件状语从句，但will表示意愿或决心时，可用于条件状语从句。
If you will read the book, I'll lend it to you.
如果你愿意读这本书，我会把它借给你。
If you will give up smoking, your health will improve.
如果你愿意把烟戒掉的话，你的健康状况就会好转。
6．will和would可表示推论或猜测。
The patient took the sleeping pills an hour ago. He will be asleep now.
病人一小时前吃的安眠药，现在应该睡着了。
It would be about ten when he left home.
他大约在十点钟离开的家。
I thought he would have told you about it.
我认为他已告知你此事。
It would be raining when she went home.
她回家时可能正在下雨。
比较：
Would you like ...表示邀请
Do you like ...表示习惯
——Do you like going go the cinema
你喜欢看电影吗？
——Yes,I go to the cinema a lot.
是的，我经常去看电影。
——Would you like to go to the cinema tonight
今天晚上去看电影好吗？
——Yes,I'd love to.
非常乐意。
E．shall和should
1．shall
①表示征询意见或请求指示，用于一、三人称疑问句。
Shall I carry it for you
我来帮你搬它，好吗？
Shall we sing a song
我们唱一支歌，好吗？
Shall they wait outside
让他们在外面等吗？
Shall the waiter bring meals to your room
要服务员把饭送到你房间去吗？
提示：
Shall I open the window
我打开窗子好吗？
Will you open the window
你打开窗子好吗？
Shall he open the window
他打开窗子好吗？
②表示说话人的意愿，有“命令、允诺、警告、决心”等意思，用于第二、三人称陈述句中。
You shall do as I say.
按我说的做。（命令）
He shall be sorry for it one day, I tell you.
我告诉你，总有一天他会后悔的。（警告）
You shall fall behind in your exam if you keep playing.
如果你一直玩，你就会在考试中落后。
Nothing shall stop us from carrying out the plan.
什么也阻止不了我们执行这项计划。（决心）
He shall have the book when I finish reading.
我看完这本书就给他看。（允诺）
I shall do my homework after reading this story book.
读完这本故事书后我就做作业。
2．should
①表示义务，意为“应该”（某件事宜于做），用于各种人称。
Children should obey their parents.
儿童应该服从他们的父母。
One shouldn't be selfish.
人千万别自私。
Customers who get bad service should complain, shouldn't they
没有得到满意服务的顾客应该抱怨，不是吗？
②常与what, how, why等词连用，表示意外、惊讶等情绪。
How should I know
我怎么会知道呢
Why should I fear
我为什么会害怕？
What should she do but cry for help
除了呼救外，她还能干什么？
I don't know why you should think I did it.
我真不知道你凭什么认为这件事是我干的。
③表示对过去、现在或将来情况的某种推测，可译为“可能、照说应该”。
It should be fine tomorrow.
明天可能天是晴天。
He should be taking a bath now.
他可能在洗澡。
It's nearly seven o'clock. Jack should be here at any moment.
已经快七点了，杰克随时都可能到这儿。
The film should be very good as it is starring first-class actors.
这部新电影是一流演员主演的，估计拍得很好。
④表示对现在或以前的动作的责怪、批评（应做的事却没做）。
The boys shouldn't be playing football. They should be at school.
这些男孩子不应该在踢足球，他们应该在上课。
You shouldn't have entered the teachers' office without permission.
没有允许你们不应该进老师办公室。
F．ought to
1．表示义务，意为“应该”（因责任、义务而该做），口气比should稍重。
We ought to defend our country.
我们应当保卫我们的国家。（每一个公民应尽的义务）
You ought to respect your parents.
你应当尊敬你的父母。
Oughtn't we to do everything possible to stop pollution
难道我们不应当尽可能地制止污染吗？
2．表示推测，暗含很大的可能，可译为“应该是，会是”。
Prices ought to come down soon.
价格可能会很快下跌。
Han Mei ought to know his telephone number.
韩梅该知道他的电话号码。
There's a fine sunset; it ought to be a fine day tomorrow.
今天有晚霞，明天应该是个好天。
3．ought to和should一样，表示对现在或以前应做的事却没做的责怪、批评。
You ought to be washing your clothes. Why are you playing Ping-Pong
你应该在洗衣服（可是你没洗）。为什么你在打乒乓球？
You ought to have handed in the exercise last week.
你上周就应当交练习。（可你没交，含责备的意思。）
He ought to have asked me before he took my bike.
他在用我自行车之前应该和我讲一声。
4．ought to与should的比较。
ought to和should的含义较近，但不完全相同。ought to表示“应该”，是从“义务”或“按理推断”的角度来讲的。should则是从说话人的个人看法这一角度来讲的。
You are her mother. You ought to look after her.
你是她的母亲，你应当照管她。（是道义上的责任，不能和should互换。）
We should encourage him for we are his classmates.
我们应该鼓励他，我们是他的同班同学啊！
提示：
表示“义务”时，我们在口语中可以用had better或be supposed to来代替should和ought to。
If you are not well, you had better ask Alice to go instead.
如果你不舒服，你最好叫艾丽丝代替你去。
I'm supposed to be there at 8 o'clock.
我应该八点到那里。
G．used to
1．used to表示过去的习惯或过去某时期的状况，但现在已不存在。
He used to drink tea but now he drinks coffee.
他过去总是喝茶但现在他喝咖啡了。（强调现在不喝茶了）
I know where there used to be a river here.
我知道这儿以前哪里有条河。（现在没有河了）
When I was a child I didn't use to like tomatoes.
我小时候不喜欢吃西红柿。
He is not what he used to be.
他已不是原来的他了。
Where did you use to live before you came here
来此之前你住在什么地方？
2．would和used to的用法区别。
①used to表示过去与现在或过去某时与后来的情况有不同，强调“现已无此习惯了”，而would只表示过去的情况，与现在无关。
When he was young, he would smoke a lot.
他年轻时总是吸许多烟。（不含有和现在比较，现在他也许还在抽，也许不抽了。）
He used to live in the country, but now he lives in the city.他过去住在乡下，现在住在城里。
②used to可表示过去的习惯动作或状态，而would只表示过去的习惯动作。
Kate used to be very thin.
以前凯特非常瘦。
There used to be a building at the street corner, but it has been pulled down.
街道拐角处过去有座楼房，现在拆了。（不用would）
③used to可泛指过去的习惯动作或状态，而would表示过去的习惯动作时，往往要带有一个特定的时间状语。
【误】We would play hide-and-seek in the fields.
【正】We used to play hide-and-seek in the fields.
我们过去常在田野里玩捉迷藏。
【正】Whenever we were in the country, we would play hide-and-seek in the fields.
每当我们在乡下，我们都在田野里玩捉迷藏。
H．dare
dare既可用作情态动词，也可用作行为动词，指勇气和胆量上的可能，可译为“敢”。
1．情态动词dare
①dare作为情态动词时主要用于疑问句和否定句，一般不用于肯定句中。
I dare not daren't walk through the forest at night.
我不敢在黑夜穿过森林。
--- Dare you walk through the forest at night
你敢在黑夜穿过森林吗？
--- Yes, I dare.
是的，我敢。
--- No, I daren't.
不，我不敢。
He dare not drive too fast on the rainy day.
下雨天他不敢开得太快。
He dared not do it last year.
去年他不敢做这事。（dare的过去时为dared）
②可以用于表示怀疑的名词性从句中。
I wonder how he dare say such things.
我真奇怪他怎么竟敢说出这样的话。
We don't know whether he dare climb the mountain.
我们不知道他是否敢爬那座山。
③可以用于条件状语从句中。
If the enemy dare enter the village, we'll fight against them to the end.
如果敌人敢进入村里，我们就和他们战斗到底。
If you dare cheat in your exam, I will give you some punishment.
如果你们敢在考试中作弊，我就惩罚你们。
2．行为动词dare
①dare可以作为行为动词，多用于肯定句中，但也可用在疑问句和否定句中
He will dare any danger.
他敢面对任何危险。
He dared me to jump over the stream.
他激我跳过小溪。
Did anyone dare to admit it
有人敢于承认吗？
I have never dared (to) go back to take a look.
我再也不敢返回去看一眼了。（否定句中to可省略）
②和其他行为动词一样，dare在句子中要随着主语的人称和数发生变化。
He doesn't dare to walk at night.
他不敢走夜路。（作行为动词）
He daren't walk at night.
他不敢走夜路。（作情态动词）
Does he dare to walk at night
他敢走夜路吗？（作行为动词）
Dare he walk at night
他敢走夜路吗？（作情态动词）
He didn't dare to walk at night fifteen years ago.
15年前他不敢走夜路。（作行为动词）
He daren't walk (=dared not walk) at night fifteen years ago.
15年前他不敢走夜路。（作情态动词）
Will you dare to do the same experiment tomorrow
明天你敢做同样的实验吗？（作行为动词）
Dare you do the same experiment tomorrow？
明天你敢做同样的实验吗？（作情态动词）
必背：
英语口语中dare的几个常用结构：
●I dare say...
我想,大概,可能,或许……
I dare say things will improve.
我想情况会好转的。
●How dare you ...
你怎么敢……？
How dare you ask me such a question
你怎么敢问我这样的问题？
●I dare you ...
我谅你也不敢……
I dare you to tell your parents!
我谅你也不敢告诉你父母！
I．need
1．情态动词need
need和dare一样，作为情态动词时，主要用于否定句和疑问句，一般不用于肯定句中（在肯定句中常被must, have to, ought to, should等情态动词取代）。作为情态动词，它的词形只有need一种形式。
You needn't return the book now. You can keep it till next week if you like. 你现在不必还书， 如果愿意，你可以下周还。（needn't = don't have to）
Need I hand in my homework now
我现在就要交家庭作业吗？
--- Need he finish the article next week
他要下个星期完成这篇文章吗？
--- Yes, he must.
是的，他必须完成。
--- No, he needn't.
不，他不需要。（= he doesn't have to）
2．行为动词need
need和dare一样，也可以作行为动词，可用于肯定句、否定句和疑问句中。行为动词need有人称和数的变化。
Plant needs water.
植物需要水。
My shirt needs a button.
我的衬衫需要一枚钮扣。
My car needs repairing.
我的车该修理了。
He has grown up. We don't need to worry about him.
他已经长大了，我们不必为他担心。
You don't need to buy so many things for the picnic.
你不必为这次野餐买这么多东西。
Patience is needed for that job.
干那工作，需要耐心。
提示：
Need作为情态动态时，不要用于肯定句中。
【误】She need do her homework by herself. (need作为情态动词时，不用于肯定句中)
【正】She needs to do her homework by herself.
她该独立完成家庭作业。
“情态动词+have done”是情态动词的一个十分重要的结构，这种结构有两个主要的用法。
表示对过去发生的动作或状态的推测或估计
may might have done
表示“大概已经”
通常用于肯定句和否定句。
might有时可用于疑问句。
can could have done
表示“可能已经”
通常用于疑问句和否定句。
could有时可用于肯定句。
must have done
表示“一定已经”
只用于肯定句，具有较大的可能性
should have done表示“该”,可能性较小
表示对过去发生的动作的遗憾或责备
might have done
表示“本可以
通常用于肯定句
could have done
表示“本可以
通常用于肯定句。
should have done
表示“应该
可用于肯定句、否定句和疑问句。
ought to have done
表示“应该”
同should have done。
needn't have done
表示“本没有必要”
只用于否定句。
A．may /might /have done
1．表示对过去事实不大肯定的推测，常译为“可能已经”。
They might have taken a later train.也许他们乘坐的是晚一点儿的火车。
He seems to know the city quite well. He may have been there before.他似乎对那个城市很熟悉，他以前可能去过那儿。
2．表示“本来应该或可以做但没有做某事”，含有轻微的责备口吻或遗憾。
You might have given him more help, though you were busy.你本来应该给他更多的帮助，虽然你很忙。
The proposal might have been refused.这个建议本该拒绝的。
B．cancould have done
1．表示对过去事实的推测，常用于否定句和疑问句。
He can't couldn't have watched TV yesterday for he knew they would have an exam.昨天他不可能看电视，因为他知道快要考试了。
I don't know why she didn't call me yesterday. Can (Could) she have forgotten my telephone number我不知道昨天她为什么没给我打电话，难道她会把我的电话号码忘了吗？
He didn't come to school yesterday. Can he have been ill他昨天没来学校，难道他生病了？
2．could可表示对过去能做而未做的事感到惋惜、遗憾，可译成“本来是可以……的”。
Why didn't Sophie apply for the job She could have got it.为什么索菲不申请这项工作？她本来是能得到的。
Why did you stay at a hotel when you went to New York You could have stayed with Barbara. 你到纽约时为什么住宾馆？你完全可以和芭芭拉住在一起的。
Given more time, we could have done the work better.如果给我们更多的时间，我们完全可以把这项工作干得更好。
C．must have done
1．表示对过去事实有把握的推测，具有较大的可能性。只用于肯定句中，否定句和疑问句用cancould have done。
His watch must have stopped.他的表肯定停了。
--- I rang your flat yesterday. A man answered but I didn't recognize the voice.昨天我给你家打电话，一位男士接了电话，但我没听出来是谁的声音。
--- Oh, it must have been my brother Peter. 哦，那一定是我哥哥彼得。
2．用于虚拟语气中时，表示与过去事实相反。
You must have caught the bus if you had got up earlier. 如果你早一点儿起床的话，你准能赶上那一班公共汽车了。（事实上没有赶上公共汽车）
He must have won the game if he had been careful enough.如果他足够细心的话，他准能赢得比赛。.
D．needn't have done
用于对过去的责备，表示“没有必要做某事，可是做了”。
The airport is close to us. You needn't have hurried there early.机场离这儿很近，你没必要早早地赶到那里。（可是你早早地到那儿了）
He is still young. You needn't have sent him such an expensive present.他还小，你没必要送他这么昂贵的礼物。
注意：
如表示“过去不必做也没有做”之意，需用didn't need to do。
It is not cold today. I didn't need to take the thick sweaters out.今天天气不冷，我没有必要把厚毛衣拿出来。（实际上也没拿）
E．shouldought to have done
1．表示对过去动作的责备或批评。
You should have gone over your lessons. (In fact you didn't go over your lessons.)你们应把功课复习好的。（可事实上你们没有。）
You shouldn't have watched TV last night. (In fact you watched TV last night.)你们昨天晚上本不该看电视。（可你们看了。）
You oughtn't to have entered the teachers' office without permission.没有经过允许，你们本不该进老师的办公室。
You oughtn't to have gone to the deserted place alone. 你不该独自去那荒凉之地。
2．表示期待或推测。
If the flight was on time, you should ought to have arrived in Shanghai early this morning.如果航班准点的话，你今早就能到上海了。
The building should ought to have been completed by the end of the week.这幢建筑物本周末前应该能完工。
F．would have done
表示与过去事实相反的假设或结果。
I would have been happy to see him, but I didn't have time.我会很高兴和他见面的，但我没时间见他。
If your father had still been alive, he would have felt very proud of you.你父亲如果还健在的话，他会为你骄傲的。
动词不定式
此处待更新
综合自：
https://m.yixuela.com/article/94
https://m.yixuela.com/article/93
https://m.yixuela.com/article/92