Question

can和be able to的区别

Answer 1

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 2

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.

Answer 3

(1) be able to 强调通过努力而获得的能力，而can则强调自身已具有的能力。如：
She can sing the song in English. 她能用英语唱这首歌。
He will be able to sing this song in English in a few minutes, too. 几小时之后，他也能用英语唱这首歌。
(2) be able to 强调一种结果，而can只强调一种可能。如：
Luckily, he was able to escape from the big fire in the end. 幸运的是，他终于逃出了大火。
If he got here a few hours earlier, I could save him. 要是他早几小时来，我还能救他。
(3) be able to 可以有各种时态；而can只有一般现在和一般过去两种时态。如：
I could help you last night, but you didn’t come. 昨天晚上我能帮你，而你又没来。
Can you see it there? 你能看见它在那儿吗？
He is / was / will be able to help you. 他能帮你的忙(from www.yygrammar.com)。
(4) can可用于表示可能性，推测，允许等情况，而be able to通常不这样用。