英语语法要点大全：情态动词
教书育人楷模，更好地指导我们的学习，让自己不断成长。让大家一块到学习啦一块学习吧!以下是学习啦我们为大伙编辑的英语基础语法文章，欢迎大伙阅读！
21.1 情态动词的语法特点
1) 情态动词不可以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，后面只能接不带to 的不定式。
3) 情态动词无人称，数的变化，即情态动词第三人称单数不加-s。
4) 情态动词没非谓语形式，即没不定式，分词，等形式。
21.1 情态动词的语法特点
1) 情态动词不可以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，后面只能接不带to 的不定式。
3) 情态动词无人称，数的变化，即情态动词第三人称单数不加-s。
4) 情态动词没非谓语形式，即没不定式，分词，等形式。
21.2 比较can 和be able to
1)can could 表示能力;可能 ,
只用于目前式和过去式。be able to可以用于各种时态。
They will be able to tell you the news soon. 他非常快就能对你说消息了。
2)只用be able to
a. 坐落于助动词后。
b. 情态动词后。
c. 表示过去某时刻动作时。
d. 用于句首表示条件。
e. 表示成功地做了某事时，只可以用was/were able to， 不可以用could。
He was able to flee Europe before the war broke out.
= He managed to flee Europe before the war broke out.
注意：could不表示时态
1)提出委婉的请求，。
--- Could I have the television on?
--- Yes, you can. / No, you cant.
2)在否定，疑问句中表示推断或怀疑。
He couldnt be a bad man.
他不大可能是坏人。
21.3 比较may和might
1) 表示允许或请求;表示没把握的推断;may 放在句首，表示祝愿。
May God bless you!
He might be at home.
注意： might 表示推断时，不表示时态。只不过可能性比may 小。
2) 成语： may/might as well，后面接不带to 的不定式，意为可以。
If that is the case, we may as well try.
典型例题
Peter ___come with us tonight, but he isnt very sure yet.
A. must B. may C. can D. will
答案B. 表可能性只可以用may. 此句意可从后半句推出。
21.4 比较have to和must
1) 两词都是需要的意思，have to 表示客观的需要， must 表示说话人主观上的怎么看，既主观上的必要。
My brother was very ill, so I had to call the doctor in the middle of the night. 我弟弟病得非常厉害，我只得半夜里把大夫请来。
He said that they must work hard. 他说他们需要努力工作。
2) have to有人称、数、时态的变化，而must只有一种形式。但must 可用于间接引语中表示过去的必要或义务。
He had to look after his sister yesterday.
3) 在否定结构中： dont have to 表示不必
mustnt 表示禁止，
You dont have to tell him about it. 你不必须要把此事告诉他。
You mustnt tell him about it. 你绝对不要把这件事告诉他。
21.5 must表示推断
1) must用在一定句中表示较有把握的推断，意为肯定。
2) must表对目前的状况或目前正发生的事情的推断时， must 后面一般接系动词be 的原形或行为动词的进行式。
You have worked hard all day.You must be tired. 你辛苦干一整天，肯定累了。
He must be working in his office. 他肯定在办公室工作呢。
比较：
He must be staying there.
他目前一定呆在那里。
He must stay there.
他需要呆在那。
3) must 表示对已发生的事情的推断时，must 要接完成式。
I didnt hear the phone. I must have been asleep. 我刚刚没听到电话，我想来是睡着了。
4) must表示对过去某时正发生的事情的推断，must 后面要接不定式的完成进行式。
---Why didnt you answer my phone call?
---Well, I must have been sleeping, so I didnt hear it.
5) 否定推断用cant。
If Tom didnt leave here until five oclock, he cant be home yet. 假如汤姆五点才离开这儿，他此时肯定还未到家。
21.6 表示推断的使用方法
can, could, may, might, must 皆可表示推断，其使用方法如下：
1)情态动词+动词原形。
表示对目前或以后的状况的推断，此时动词一般为系动词。
I dont know where she is, she may be in Wuhan.
2)情态动词+动词目前进行时。
表示对目前或以后正在进行的状况进行推断。
At this moment, our teacher must be correcting our exam papers.
这个时候，大家老师想来在批改试题。
3)情态动词+动词完成时。
表示对过去状况的推断。
We would have finished this work by the end of next December.
明年12月底前大家非常可能已完成这项工作了。
The road is wet. It must have rained last night.
地是湿的，昨天晚上肯定下雨了。
4)情态动词+动词的目前完成进行时。
表示对过去正在发生事情的推断。
Your mother must have been looking for you.
你母亲肯定一直在找你。
5)推断的否定形式，疑问形式用cant, couldnt表示。
Mike cant have found his car, for he came to work by bus this morning.
迈克肯定还没找回他的车，由于早上他是坐公共汽车来上班的。
注意：could, might表示推断时不表示时态，其推断的程度不如can, may。
21.7 情态动词+ have +过去分词
1) may have + done sth, can have + done sth 表示过去，推断过去时间里可能发生的事情。
Philip may have been hurt seriously in the car accident.
Philip can have been hurt seriously in the car accident.
2) must have +done sth，对过去时间里可能发生的事情的推断，语气较强，具备一定，谅必的意思。
---Linda has gone to work, but her bicycle is still here.
---She must have gone by bus.
3) ought to have done sth, should have done sth
本应该做某事，而事实上并没做。否定句表示不该做某事而做了。
You ought to have been more careful in this experiment.
He ought not to have thrown the old clothes away.
ought to 在语气上比should 要强。
4) neednt have done sth 本不必做某事
I dressed very warmly for the trip, but I neednt have done so. The weather was hot.
5) would like to have done sth 本计划做某事
I would like to have read the article, but I was very busy then.
21.8 should 和ought to
should 和ought to 都为应该的意思，可用于各种人称。
---Ought he to go?
---Yes. I think he ought to.
表示需要，命令时，语气由 should、had better最好)、must渐强。
21.9 had better表示最好
had better 等于一个助动词，它只有一种形式，它后面要跟动词原形。
had better do sth
had better not do sth
It is pretty cold. Youd better put on my coat.
Shed better not play with the dog.
had better have done sth表示与事实相反的结果，意为本来最好。
You had better have come earlier.
21.10 would rather表示宁可
would rather do
would rather not do
would rather than 宁可而不愿。
还有would sooner, had rather, had sooner都表示宁可、宁愿的意思。
If I have a choice, I had sooner not continue my studies at this school.
I would rather stay here than go home. = I would stay here rather than go home.
典型例题
----Shall we go skating or stay at home?
----Which ___ do?
A. do you rather B. would you rather C. will you rather D. should you rather
答案B。本题考查情态动词rather的使用方法，would rather +do sth 意为宁可，本题为疑问句，would 提前，所以选B。
21.11 will和would
注意：
1)would like; Would like to do = want to 想要，为固定搭配。
Would you like to go with me?
2)Will you? Would you like? 表示一定含义的请求劝说时，疑问句中通常用some, 而不是any。
Would you like some cake?
3)否定结构中用will，通常不需要would, wont you是一种委婉语气。
Wont you sit down?
21.12 情态动词的回答方法
问句 一定回答 否定回答
Need you? Yes, I must. No,I neednt
Must you? /dont have to.
典型例题
1)---Could I borrow your dictionary?
---Yes, of course, you____.
A. might B. will C. can D. should
答案C.could表示委婉的语气，并不为时态。答语中of course，表示一定的语气，允许某人做某事时，用can和 may来表达，不可以用could或might。复习： will 与you连用，用来提出需要或下命令。should与you 连用，用来提出劝告。
2)---Shall I tell John about it?
---No, you ___. Ive told him already.
A. neednt B. wouldnt C. mustnt D. shouldnt
答案A。neednt 不必，不需要。 wouldnt 将不, 不会的。 mustnt 禁止、不可以。 shouldnt 不应该。本题为无需，不必的意思，应用neednt。
3)---Dont forget to come to my birthday party tomorrow.
---______.
A. I dont B. I wont C. I cant D. I havent
答案B. will既可当作情态动词，表请求、建议、也可作为实义动词表意愿、意志、决心，本题表示决心，选B。
21.13 带to 的情态动词
带to 的情态动词有四个：ought to, have to, used to, be to, 如加上have got to ,, be able to，为六个。它们的疑问，否定形式应予以注意：
Do they have to pay their bill before the end of the month?
She didnt use to play tennis before she was fourteen.
You ought not to have told her all about it.
Ought he to see a heart specialist at once.?
ought to 本身作为情态动词用。其他的词作为实义动词用，变疑问，否定时，须有do 等助动词帮助。
典型例题
Tom ought not to ___ me your secret, but he meant no harm.
A.have told B.tell C.be telling D. having told
答案A。因为后句为过去时，告诉秘密的动作又发生在其前因，此地应用过去完成时，但它在情态动词 ought to 后，所以用have。
21.14 比较need和dare
这两词既可做实义动词用，又可做情态动词用。作为情态动词，两者都只可以用于疑问句，否定句和条件句。 need 作实义动词时后面的不定式需要带to，而dare作实义动词用时, 后面的to 时常可以被省略。
1) 实义动词： need
need + n. / to do sth
2) 情态动词： need，只用原形need后加do，否定形式为need not。
Need you go yet?
Yes, I must. / No, I neednt.
3) need 的被动含义：need, want, require, worth后面接doing也可以表示被动：
need doing = need to be done
