In this video (at 3:43) some guy said to me that I can’t use “could” to talk about negative possibilities. (Some people said to “By-word”). Is it true? Why do people say so and why do you think why?

What is your channel here https://www.youtube.com/watch? Which

ones aren’t ready?

He may not be able to help you.

When you put a ‘could’ and’should’ in one sentence, it is too long. He

can’t use ‘should’ too well though.