- We use the modal verb can or can't to express ability (= capacity) or inability to do something in the present.
Example: I can do it. / He can't drive. / Can you swim?
- However, to talk about general ability or inability to do something in the past, we use the modal verb 'could' or 'couldn't'.
Example: I could swim when I was four. / My grandmother couldn't speak French.
- Nevertheless, for questions in the past, we prefer to use 'was/were able to' + infinitive.
Example: Were you able to lift the cupboard? / Was he able to reach the top?
Important! The reason why we don't use 'could' in questions to talk about ability is because it can also be used in the present with a more polite meaning to ask for permission:
Example: Can I take this chair? - more informal
Could I take this chair? - more polite
- 'Can' has no future form: we use the future form 'will be able to' to talk about ability in the future.
Example: I will soon be able to play again. / He'll be able to swim after a few lessons.
- 'Can' y 'could' también se usan para hablar de permiso (=tener permiso/libertad para hacer algo o pedir permiso). 'Can' es informal y 'could' es formal.