Expressing Ability

ABILITY : CAN, COULD, BE ABLE TO
1.- Present ability
                         Can, can’t: I can swim (I know how to swim)  I can lift it  ( I am able to lift it)
2.- Future ability
                          Can : I can come tomorrow (future reference)
                           Be able to : he will be able to come next week
3.- Past ability
                          Could, couldn’t: When I was ten, I could swim 
                          could vs be able to
He was a good swimmer, and could save people’s lives (we don’t  know)  
He was a good swimmer, and was able to save people’s lives (he actually did it)
                          could have
He was a good swimmer and could have saved people’s lives ( he didn’t use his ability)

Practice: Complete the sentences:
a.- There was a woman with a big hat in front of me. I ____________see a thing.
b.- I’m sorry you are in my light. I __________see what I’m doing.
c.- He had a strange ability: he _______________ move his ears really fast.
d.- She _____________ done it, but she left without trying.  
e.- When he was young he____________ run a marathon once, but he________ now.


Solutions:

a.- wasn't able to
b.- can't
c.- could
d.- could have
e.- was able to/ can't