Can, Could, Be Able to

"Can," "could," and "be able to" are all expressions that convey the ability to do something. However, there are some subtle differences between them.

"Can" is used to express present ability or capability. It indicates that someone is presently able to do something. For example, "I can swim" means that I have the ability to swim right now.

"Could" is the past tense of "can" and is used to express past ability or capability. It indicates that someone was able to do something in the past. For instance, "When I was younger, I could run faster" suggests that in the past, I had the ability to run faster.

On the other hand, "be able to" is a phrase used to express both present and future ability. It can be used interchangeably with "can" and "could" in many cases. However, "be able to" offers more flexibility in terms of tense and is often used when the sentence structure requires it. For example, "He will be able to join us tomorrow" implies that in the future, he will have the ability to join us.

In summary, "can" is for present ability, "could" for past ability, and "be able to" covers both present and future ability.