1.
Can, Could, Be able to
modals

2.
You use CAN to You can also use BE
describe an ability in ABLE TO to describe an
the present. ability in the present.
 Annie can swim, but  He's able to park a car,
she can't ride a bike. but he's not able to
 I can play the guitar drive in traffic yet.
and sing.  He’s crazy. He thinks
he is able to stop time
with his mind.

3.
You use CAN to You can also use BE
describe an ability in ABLE TO to describe an
the present. ability in the present.
 Annie can swim, but  He's able to park a car,
she can't ride a bike. but he's not able to
 I can play the guitar drive in traffic yet.
and sing.  He’s crazy. He thinks
he is able to stop time
with his mind.
In the PRESENT, the only difference between CAN and
BE ABLE TO, is that CAN is more common and BE
ABLE TO is more formal.

4.
use WAS/ WERE ABLE TO
if you are talking about
use COULD to describe a what happened in a
general ability in the past. particular situation.
 My father could speak  Jack and John played a
five languages. tennis match yesterday
 He was a very good and John was able to
tennis player. He could beat Jack.
beat anybody.  There was a fire, but we
were able to scape.

5.
But in the negatiave, you can use COULDN’T in both
cases:
 My father couldn’t  There was a big fire
swim. and some people
 I couldn’t read when coulnd’t escape.
I was 5.  Yesterday Jack
couldn’t beat John.

6.
For forms and tenses other than present or past, you
have to use BE ABLE TO.
 We haven't been able to play tennis for a long
time. (Present Perfect)
 I won’t be able to be there tomorrow.
(Future)
 I’ve always wanted to be able to dance. (To-
infinitive)
 etc.