■兩者均可表示能力，有時(shí)可互換：
He can [is able to] drive. 他會(huì)開車。
He was able to [could] run very fast. 他可以跑得很快。
■但兩者有以下區(qū)別需注意：
(1) 表示過去一般性能力，用 could 和 was (were) able to 均可，但若表示過去特定場(chǎng)合的能力，則通常用 was (were) able to，而不用 could。
(2) be able to 不僅有多種時(shí)態(tài)形式(通常不用于進(jìn)行時(shí)或與 be going to 連用), 而且還可以與某些情態(tài)動(dòng)詞連用(通常不與 can 連用), 甚至還可以有非謂語(yǔ)形式：
He has not been able to go to school for a week. 他已有一周不能上學(xué)了。
You might be able to persuade him. 你也許能夠說服他。
I hope to be able to do the work. 我希望能干得了這項(xiàng)工作。
I regret not being able to help her. 我很遺憾未能幫助她。
以上用法中的 be able to 均不能用 can 替換。
He can [is able to] drive. 他會(huì)開車。
He was able to [could] run very fast. 他可以跑得很快。
■但兩者有以下區(qū)別需注意：
(1) 表示過去一般性能力，用 could 和 was (were) able to 均可，但若表示過去特定場(chǎng)合的能力，則通常用 was (were) able to，而不用 could。
(2) be able to 不僅有多種時(shí)態(tài)形式(通常不用于進(jìn)行時(shí)或與 be going to 連用), 而且還可以與某些情態(tài)動(dòng)詞連用(通常不與 can 連用), 甚至還可以有非謂語(yǔ)形式：
He has not been able to go to school for a week. 他已有一周不能上學(xué)了。
You might be able to persuade him. 你也許能夠說服他。
I hope to be able to do the work. 我希望能干得了這項(xiàng)工作。
I regret not being able to help her. 我很遺憾未能幫助她。
以上用法中的 be able to 均不能用 can 替換。