Grammar about Can , could, be able to

I can ride a bike.

We use can / could to talk about abilities.

“Can” for present ability, “Could” for past ability.

She can sing a song

He could swim when he was a child.

We could walk on our hands.

I’m sad.

You could go to the park.

We use can / could to talk about possibilities suggestions.

In this case van and could both refer to present time.

She has a headache.

She can take this painkiller.

I am really tired.

You could go to bed.

We don’t have enough money.

You can work harder.

Can I go out of class?

We use can / could to request or get a permission.

In this case again can and could are used for present time. Can is less formal than could.

Could I borrow your book?

Can I use your laptop?

Could you lend me your car tonight?

I must be able to finish my project.

We will be able to travel to moon.

I prefer to be able to drive a car to ride a bike.

Being able to swim is vital.

I have never been able to talk to her in person.

In the past people weren’t able to read and write