EGrammar Unit 25 Can, Could, and be able to

We use "can" to say that something is possible or that somebody has the ability to do something
何かが可能なことを言う時、誰かが何かを出来るときとかに[can]を使います。

"be able to" is possible instead of "can", but "can" is more usual.
But "can" has two forms, can and could. So sometimes it is necessary to use "be able to"
be able to"を"can"の代わりに使うことが出来ます。でも、"can"を使った方がより自然です。また、canはcan/couldの二つの形しかないので場合によってはbe able toを使う必要があります。

We can see the ocean from our hotel window.
Can you speak any foreign languages?
The word "dream" can be a noun or a verb.
I'm afraid I can't come to your party on Friday.
Are you able to speak any foreign languages?
I can't sleep.
I haven't been able to sleep recently.
Tom can come tomorrow.
Tom might be able to come tomorrow.

"Could" and "was able to"

Sometimes "could" is the past of "can". We use "could" especially with:

see hear smell feel remember understand

We also use "could" to say that somebody had the general ability or permission to do something.

We use "could" for general ability. But if we are talking about what happened in a particular situation, we use "was/were able to" or "managed to".

The fire spread through the building quickly, but everybody was able to escape. (or ...everybody managed to escape.)
Thy did not want to come with us at first, but we managed to persuade them.

jack was an excellent tennis player. He could beat anybody.

• he had the general ability to beat anybody

Jack and Ted played tennis yesterday. Ted played very well, but in the end jack managed to beat him. (he managed to beat him this time)

The negative "couldn't"is possible in all situations: