如梦令赏析:The difference of "be able to " and "can "

比较can 和be able to

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。

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 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.

没有太大区别，但是be able to更有 有能力做……
i am able to study well.
我有能力把学习搞好
can用的要更加广泛
can you help me?你能帮我吗？
这时一般不用be able to

can表示"能够"
I can play football.我会踢球.
be able to表示"有能力"
I was able to help her with her homework,but I didn't.我可以帮她完成作业,但我没那么做.