Collins Cobuild

Unit 83
Ability
Main points
You use ‘can’ to talk about ability in the present and in the future.
You use ‘could’ to talk about ability in the past.
You use ‘be able to’ to talk about ability in the present, future, and
past.
1
You use ‘can’ to say that someone has the ability to do something.
You can all read and write.
Anybody can become a qualified teacher.
You use ‘cannot’ or ‘can’t’ to say that they do not have the ability to
do something.
He cannot dance.
I can’t speak German.
2
When you want to talk about someone’s ability in the past as a result
of  a  skill  they  had  or  did  not  have,  you  use  ‘could’,  ‘could  not’,  or
‘couldn’t’.
He could run faster than anyone else.
A lot of them couldn’t read or write.

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3
You also use ‘be able to’, ‘not be able to’, and ‘be unable to’ to talk
about  someone’s  ability  to  do  something,  but  ‘can’  and  ‘could’  are
more common.
She was able to tie her own shoelaces.
They are not able to run very fast.
Many people were unable to read or write.
4
You use ‘was able to’ and ‘were able to’ to say that someone managed
to do something in a particular situation in the past.
After treatment he was able to return to work.
The farmers were able to pay the new wages.
We were able to find time to discuss it.
 WARNING:  You  do  not  normally  use  ‘could’  to  say  that  someone
managed to do something in a particular situation. However, you can
use ‘could not’ or ‘couldn’t’ to say that someone did not manage to do
something in a particular situation.
We couldn’t stop laughing.
I just couldn’t think of anything to say.
5
When you want to say that someone had the ability to do something in
the  past,  but  did  not  do  it,  you  use  ‘could  have’  followed  by  a  past