2017届高考英语考前冲刺精选情态动词
情态动词无人称和数的变化，但却有一定的意义，表示一种看法。英语中的情态动词有: can, could, may, might, shall, should, will, would, must, ought to, need, dare, used to.
1. can 与could
1) 能力：
I can do it well.
He couldn’t support his family with his few pay.
2) 可能性或允许：
She can be free this afternoon.
She asked me if she could take the books of the library.
3) 表示惊异、怀疑等：
What you told me can’t be true.
How can (could) you be so careless!
4) could 可以委婉提出问题和看法，还可以用于虚拟语气中。
Could you give me some help?
I would help you if I could.
2. can与 be able to
can (could) 表示能力、可能性、允许、迟疑情绪等；be able to 只表示能力，可以有更多的时态形式。
表示能力，二者通用。
I can answer the question. = I am able to answer the question.
No one could answer the question. = No one was able to answer the question.
I’m sorry. I haven’t been able to answer your letter.
表示可能、允许、推测时用can。
You cannot do it well.
You can go now.
Can I do it in this way?
You could have finished the work, but …
3. may 与might(过去式)
1) 表示允许。“可以”
May I come in?
He asked me if he might come in.
---May I come in?
---Yes, please. Certainly.
---No, please don’t. No, you mustn’t.
2) 表示可能性。
He may be at home. = Maybe he is at home.
He may be having lunch. = Maybe he is having lunch.
might 用在虚拟条件句中。
If he were here, you might get some help from him.
4. must
1) must 侧重主观看法，have to 强调客观需要。
We must do our work harder.
We have to hand in our homework before 6.
2) 在回答must 引起的问题时，否定回答用needn’t 或don’t have to .
---Must I get there before 12 o’clock?
---No, you needn’t.
3) mustn’t “一定不要，不可以”表示不许可. can’t (couldn’t)表示不可能，表示对某种情况的推测。
You mustn’t talk like that.
We mustn’t stay here any longer.
---Can I smoke here?
---No, you mustn’t.
I think he can’t be present on time.
We can’t finish so much work in a day.
4) must 可表示一种推测。
A. 对目前情况的推测
Mr. Li must be at home.
B. 对过去情况的判断
He has been away for two hours. He must have got there.
5) 有时有“偏偏，偏要”的意思。
Why must it rain today?
When I was taking a nap, a student must knock at the door.
5. need
1) 作情态动词，后跟动词原形，主要用于否定句及疑问句。
It’s so early. You needn’t hurry.
You needn’t let him know this.
Need I go with you? No, you needn’t.
Need I come? Yes, you must.
2) 作及物动词，有人称、数和时态的变化。
A: sb + need + (to do) sth.
He needed a room to live in.
He needs to do it alone. = He need do it alone.
They didn’t need to do it yourself.
You need to learn more. = You need learn more.
B: sth + need + doing / to be done
My watch doesn’t work. It needs repairing.
The question you raised needs to be discussed.
6. dare
“敢，敢于”。可作情态动词与及物动词（后跟不定式）。
He dare go home alone. = He dares to go home alone.
She dare not say what she thinks. = She doesn’t dare to say what she thinks.
I have never dared to tell him about it.
7. used to
后跟动词原形，表示过去的习惯动作或状态。
否定形式：
主语 + usedn’t to + 原形 = 主语 + didn’t use to + 原形
疑问式：
Used + 主语 + to + 原形 = Did + 主语 + use to + 原形
反意疑问句：
He used to be beaten often, usedn’t he?
= didn’t he?
8. should与ought to
ought to “应该”和should 的意思，用法差不多，只是语气稍重一点。
ought to的肯定式：主语 + ought to + 原形
ought to 的否定式：主语 + ought not to + 原形
疑问句：Ought + 主语 + to + 原形
Oughtn’t + 主语 + to + 原形
9. 情态动词+ have done 和情态动词 + be doing
1) 情态动词和动词的完成式构成谓语，表示“可能已经……”、“想必已经……”、“本来可能……”等意思，是对过去情况的判断。
He can (could) have got on a bus. 他可能已上车了。
He can have understood what you had said.
他可能已经听懂你所说的了。
She know about it. You must have told her.
她知道这事了，你肯定已经告诉她了。
He must have arrived there. 他一定到那了。
You needn’t have told them that.
你本来不必告诉他们的。
You could have done it better. 你本来可以做得更好的。
She may (might) have gone to the doctor. 她或许是去看医生了。
We ought to have given you more help. 我们本应该给你们更多的帮助的。
2) 情态动词 + be doing, 表示“……正在”的意思，是对目前正在做的情况的推测。
can be doing
可能正在做
might be working
也许正在做
must be waiting
一定在等
should be watching
应该正在观看
may be playing
也许正在玩
10. 情态动词用法归类：
1）表示“能力”的情态动词：
can, could (be able to)
2) 表示“可能，也许”、“肯定”等推测判断的情态动词：
can, could “可能”
may, might “可能，也许”
must “肯定”
should “应该”
He must be at home. 可能性相当大
He should (ought to) be at home. 可能性较大
He can (may) be at home.
有可能但不肯定
He could (might) be at home. 不及上句肯定
3）表示“请求”、“允许”、“应该”、“禁止”等情态动词。
A、can,
could, may, might
都表示请求别人允许或答复，意义上差别不大，往往可以互用。但在语气上表示客气、委婉的程度上有些差别: can (最常用) ---could（较客气）
---may（更正式客气）--- might (最客气)
B、should, ought to, must，had better
had better (最好) ---should (应当) ---ought to (应该) --- must (必须)
C、will, would 表示请求对方做某事，shall 表示征求对方意见或者用于第二、三人称后，表示允诺、命令、威胁、决心、规定等意志，“应当”。
Will you open the window?
Shall I open the window?
Tom shall have a toy if he is a good boy.
(允诺)
You shall not leave your post.
(命令)
He shall suffer for this.
(威胁)
That day shall come.
（决心）
Each competitor shall wear a number.
(规定)