Question

can和be able to的区别

求can和be able to的区别 拜托了，各位！！ 答好的，加分！！

Answer 1

1）can　could 表示能力；可能 (过去时用could),
只用于现在式和过去式(could)。be able to可以用于各种时态。
　They will be able to tell you the news soon. 他很快就能告诉你消息了。

2）只用be able to
　 a. 位于助动词后。
　 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，只能用was/were able to， 不能用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，（注意在回答中不可用could）。
　　 --- Could I have the television on?
　　 --- Yes, you can. / No, you can't.

2）在否定，疑问句中表示推测或怀疑。
　　 He couldn't be a bad man.　　
　　 他不大可能是坏人。

can用于表示“能力”时是指现在的能力，过去或将来的能力通常用was/were able to或will/shall be able to表示。

eg. She was able to go to school yesterday.
Soon she will be able to swim a quarter of a mile.

Can的过去式形式could也可用于表示泛指过去的能力。如：

I could read when I was four.

但不能用于表示特定的某一过去能力，如不能说：
*He could swim halfway before he got tired.
He was able to swim halfway before he got tired.

上述这种用法的区别不存在于否定句中。在否定句中，couldn’t与was/were not able to 可以互换使用。

eg. I couldn’t see him again before he left.
I wasn’t able to see him again before he left.

另外，要说一个阶段延续至今的能力，可用have/has been able to表示。

eg. John has been able to swim for many years.

注意的一点是：can也可以用于表示“许可”。它可以表示现在许可或将来许可，过去许可用could表示，此时一律不能用be able to的某种形式替换。

Answer 2

can 和be able to 都可以表示能力.
can泛指一般的能力,而且只有两种形式,
即:can, could．be able to 则主要指具体做到了某件事的能力，其形式主要是靠be 发生变化，所以形式比can 多．
可以说：I can swim. I am able to swim.
但是不能说：All the people could escape from the big fire in time. 只能说：All the people were able to escape from the fire in time.
can 与be able to
be able to 虽然也可以译作“能”, 但更强调“能力”
e.g., Will you be able to come?
I’m able to do the work all by myself.
两者的用法区别在于
can不能作不定式,而be able to 则能
e.g., He will ______do the work better.
A.can
B.be able to
答案为B
can不用于完成时
e.g., Now he has been able to work alone.
They have been able to use the computer since they came here.
can可用于将来时,但句中须有时间状语
e.g., You can use this machine next week.(can意为”可以”不表能力)
当然,不可以同时使用表示将来的助动词will或shall(be able to 可以)

Answer 3

be able to 可以用于某一次的行为can 不行吧