Modal Verbs

Can, could
We use can:
to say that something is possible or allowed
something has the ability to do smth.
can + infinitive (can do)
example: I can come and see you tomorrow if you like.
the negative is can’t (can not)
example: I’m afraid i can’t come to the party on Friday.
Present – can
Past – could
Future --------
We use could:
especially with words:
see hear smell taste feel
remember understand
example: As soon as I walked into the room, I could smell gas.
to say that somebody had the general ability or permission to do smth.
example: My grandfather could speak 5 languages.
the negative is couldn’t (could not)
example: Pate played well, but he couldn’t beat Mike.
Sometimes we need to use (be) able to
but can has only 2 forms:
Can (present) and could (past), so sometimes it’s necessary to use (be able to).
example:
Tom can come tomorrow.
Tom might be able to come tomorrow.
usage of can is more usual than able to.
we use could for general ability; but if you want to say that smb. did smth. in a specific situation, use was/were able to or manage to (not could)
example: we didn’t know were Anna was, but we manage to find/were able to find her in the end. (not could find)
the negative couldn’t is possible in all situations.…