To form the negative of be able to, you either put not or another negative word in front of able, or you. When i was younger i could stay up all night and not get tired. They could come by car.
Kristaps Porzingis breaks down Al Horford reunion with Warriors
You use could when you are expressing strong feelings about something by saying that you feel as if you want to do the thing mentioned, although. The negative form of could is could not or couldn't. It was so noisy that we couldn't hear ourselves speak.
You said we could watch tv.
We use could to show that something is possible, but not certain: The meaning of could is used in auxiliary function in the past, in the past conditional, and as an alternative to can suggesting less force or. (= maybe they will come by car.) they could be at home.
