第六章 情态动词
一.概念:
情态动词是表示能力,义务,必须,猜测等说话人的语气或情态的动词.
二.相关知识点精讲:
1.can
1)表能力
can表能力时意味着凭体力或脑力或技术等可以无甚阻力地去做某事

I can climb this pole. 我能爬这根杆子.
He is only four , but he can read. 他只有4岁,但已认得字了.
Fire can't destroy gold. 火烧不毁金子.
因为can不能和其他助动词连用,所以表示将来式时用will be able to
You will be able to skate after you have practiced it two or three times.
你练习两三次后就会溜冰了.
2)表可能性
多用于否定与疑问结构中,但也可用在肯定句中.
Can the news be true 这消息可能是真的吗
It can't be true. 它不可能是真的.
What can he possibly mean 他可能是什么意思
can 用在肯定句中表示理论上的可能性(一时的可能).
A horse in the center of London can cost a lot of money.
Attending the ball can be very exciting.
The road can be blocked. 这条路可能会不通的.
may 在肯定句中表示现实的可能性.
The road may be blocked. 这条路可能不通了.
3)表示允许(和may意思相近)常见于口语.
Can (May) I come in 我能进来吗
Can I smoke here 我可以在这里抽烟吗
2.could的用法
1)表过去的可能和许可,(多用于间接引语中)
At that time we thought the story could not be true.
那时我们认为所说的事不可能是真的.
Father said I could swim in the river.
爸爸说我可以在河里游泳.
2)表过去的能力
I could swim when I was only six.
我刚六岁就能游泳.
Could在肯定句中表示过去的能力时,常表抽象的一般的能力.
He could be very naughty when he was a child.
他小时候会是很顽皮的.
3)表"允许".可表示委婉客气的提出问题或陈述看法
Could I use your bike
Yes, you can.
他会记得那时吗
I'm afraid I couldn't give you an answer today.
恐怕我今天不能回答你.
The teacher said you could go to the store for sweets.
老师说你可以去商店买糖.
3)Could/can+have done 结构表示对过去发生的事情的"怀疑"或"不肯定". could 加完成式还用于肯定句时一般表过去可能完成而却未完成的动作.
Can they have won the basketball match
他们赢了那场篮球赛吗
What you referred to just now can have made her very sad.
你刚刚所谈到的可能令他很伤心.
You could have completed the task a little earlier.
你本来能早点完成任务的.(但事实上并没有提前完成任务)
I could have passed my examination easily but I made too many stupid mistakes.
我本可以轻易通过考试,但我犯了太多不该犯的错误.
如表具体做某一件事的能力时,则须用 be able to .
He was able to translate the article without a dictionary.
他可以不用词典翻译那篇文章.
Can表示一贯的能力 ,be able to表示客观能力和通过努力可以达到的能力
I can't swim. But I am sure I will be able to swim through more practicing.
The fire spread through the hotel, but everyone was able to get out
When the boat sank he was able to swim to the bank
3.may 的用法
1)表示请求,可以,允许.
You may drive the tractor. 你可以开那台拖拉机.
2)当回答由may 引起的问题时,否定答语要用must not,表示"不许可","不应该","不行".
May I come in
Yes, you may.
No,you can't
No, you may not .
No ,you mustn't
No ,you'd better not.
3) may /might 推测性用法 可能
He may be right.
He may not come today (可能不)
He may /might come tomorrow.
, 注意: 1只用于肯定和否定句中,不用于疑问句中.
2 might 比may可能性更小
He might get a job.
He may get a job.
3 may no 可能不 can not不可能
He may not come
He can't come
3)表建议(可和as well 连用)
You may(might)as well stay where you are.
你还是原地待着好.(may as well 有"还是……的好"的含义)
4)表祝愿
May you be happy!
might
1)表过去的"可能"和"允许"多用于间接引语.
She said that he might take her dictionary.
她说他可以拿她的词典去用.
除在间接引语中外,might一般不表示过去的"可能"与"许可".表过去的"可能"可用could,表过去的"许可"可用were (was) allowed to.
2)表现在的"可能",其可能性要比may小.
Electric irons could be dangerous; they might give you a severe shock.
电熨斗会有危险,它可能电着人.
3)may (might) + have +done 表示对过去发生行为的推测,含有"想必","也许是"的意思.
It may have been true. 这事也许是真的.
He might not have settled the question. 他可能尚未解决那个问题.
4.must 的主要用法.
1)表示必须,必要
We must do everything step by step .我们必须按部就班地做一切事情.
Why must you always bother me 为什么你偏要打扰我呢.
2)must be + 表语的结构,通常表示猜测,含有"一定"之意.(只用在肯定句中)
He must be an honest boy. 他一定是个诚实的男孩.
This must be your room. 这一定是你的房间.
3)must 的否定式有两个:当回答由must引起的问题时,否定答复要用needn't或don't have to 表示"不必","无须","用不着","不一定"的意义.当表示"不应该","不许可","禁止"时,就用must not.
Must I go tomorrow 明天我必须去吗
Yes, please.是的,请吧!
No , you needn't. 不,你不必去.
4)must +have +过去分词的结构,常用在肯定句中,表示对过去发生行为的推测,含有"一定","准是"的意思.否定和疑问句用can.
She must have studied English before.她以前一定学过英语.
5.have to的含义与must是很接近的,只是have to 比较强调客观需要,must着重说明主观看法.
I must clean the room.(主观想法)
I have to clean the room.(客观需要)
另外,have to 能用于更多时态:
We had to be there at ten .我们得在十点钟到那里.
We will have to reconsider the whole thing.
这一切我们将不得不重新加以考虑.
have to 的否定式:don't have to do 表示"不必做……"之意.

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