We use can to say that something is possible or allowed, or that somebody has the ability to do something. We use can + infinitive
We can see the lake form our hotel.
Can you speak foreign languages?
Be Able To
You can say that somebody is able to do something, but can is more usual.
We are able to see the lake from our hotel.
However, can has only two forms: can (present) and could (past). So sometimes it is necessary to use (be) able to.
I haven’t been able to sleep recently.
Tom might be able to come tomorrow.
Applicants for the job must be able to speak two foreign languages.
Let’s Practice What We’ve Learned
Sometimes could is the past of can. We use could especially with: see, remember, hear, smell, taste, feel, understand
We had a lovely room in the hotel. We could see the lake.
I was sitting at the back of the theater and couldn’t hear very well.
We use could for general ability and with see, hear etc.
My grandfather could speak five languages.
But to say that somebody succeeded in doing something in a specific situation, we normally use was/were able to or managed to (not could)
The fire spread quickly but everybody was able to escape. (not could escape)
I didn’t know where Max was, but I managed to find him in the end. (not could find)
The negative couldn’t (could not) is possible in all situations.
My grandfather couldn’t swim.
Andy played well, but he couldn’t beat Jack.