情态动词的用法
情态动词
（1）情态动词表示说话人对某一动作或状态的态度，或表示主观设想。情态动词有自己的词义，但不能单独作谓语动词，必须和不带to的动词不定式连用，没有人称和数的变化，常用的情态动词有can, may, must, will, shall, should, would, need, dare.
① 情态动词有自己的词义，表示说话人对某一动作或状态的态度，或主观设想。如：
You may go now.
This bus can seat 40 people.
The work must be finished as soon as possible.
② 情态动词不能单独作谓语，必须和不带to的不定式连用，没有人称和数的变化。
③ 情态动词有现在式和过去式两种形式。
（2）情态动词的用法。
① may的用法
- 表示允许或征询对方的许可，有“可以”的意思。May not表示说话人“不许可”，如：
You may go now.
May I use you typewrite?
You may not go=I do not permit you to go.
- 在回答may引导的疑问句时，肯定回答用yes, you may否定用No, you mustn’t. No, you can’t或No, you had better not.
② can的用法
a．表示能力，有“能、会、能够”的意思。
- 表示允许，在口语中代替may，有“可以的意思。
- 表示“可能性”，常用于否定句或疑问句。
The hall can hold at least 200 people.
The librarian said we could take these books.
Today is Sunday, he can’t be at school today.
- can和be able to的用法比较
can用来表达能力时，由于只有现在时和过去时两种形式，其他时态要用be able to来表达。如：
I can play piano.
He has not been able to finish the work in time.
③ must 的用法
- must表示必须，应该。如：
Must I come to the party?
The article must be completed before Friday.
- must的否定形式mustn’t, 表示“不应该、不可以、禁止”。如：
You mustn’t get to school too late.
Must I do it now? Yes, you must. No, you needn’t
She must have gone to Beijing.
You must say sorry to me for that
You mustn’t clean only own room.
④ need的用法
- need作为情态动词主要用于否定句和疑问句，较少用于肯定句。如：
I needn’t wear a coat. = I don’t think I need wear a coat.
I don’t need things like that.
⑤ shall
用于第二、第三人称，表示说话人的意愿。如:
He shall get his money.
You shall do exactly as you wish.
Shall I turn on the light?
Shall I poen the window?
⑥ would的用法
表示愿望、决心、建议或看法，如：
I would like to go there.
I promised that I would do my best.
表示过去的习惯.
He would often come to my house to see me.