Examples:I can swim.
We must hurry.Birds can fly.
WE USE COUL WHEN:
- 1 used as the past tense of ‘can’She said that she couldn't come.I couldn't hear what they were saying.Sorry, I couldn't get any more.
- 2 used to ask if you can do somethingCould I use your phone, please?Could we stop by next week?
- 3 used to politely ask somebody to do something for youCould you babysit for us on Friday?
- 4 used to show that something is or might be possibleI could do it now, if you like.Don't worry—they could have just forgotten to call.You couldn't have left it on the bus, could you?‘Have some more cake.’ ‘Oh, I couldn't, thank you (= I'm too full).
- 5 used to suggest somethingWe could write a letter to the director.You could always try his home number.
- 6 used to show that you are annoyed that somebody did not do somethingThey could have let me know they were going to be late!7 (informal) used to emphasize how strongly you want to express your feelingsI'm so fed up I could scream!
Be able to
- He is able to offer you the best price possible.
- We were able to get in to see the film.
- They haven't been able to find the missing document.
- So, you aren't able to help.
- I will be able to see you after lunch.
- They might not be able to put us up for the night.
