be able to and can??

Can or be able to are used to say that something is possible or that somebody has the opportunity to do something:

We use "be able to" to form the future and perfect tenses and the infinitive:

For example:

You'll be able to get a taxi outside the station.
I haven't been able to get much work done today.
She'd love to be able to play the piano.

But we can't use "can " to form the futrue and perfect tenses and the infinitive; these are the differences.

除了在 將來式(future tense) 等tense 格式中只能用 "be able" 的分別外; 在一般情況下, 如現在式(present tense) 或 過去式 (past tense) 時, 在語氣上, 用"be able to" 會較 "can/could" 為婉轉. 因此"can/could" 在語氣上較主觀直接及肯定, 而"be able to"形式則較客觀婉轉及較適用於傳述他人話語.