The verbs may, might and could show possibility now and in the future.
In this case, they almost have the same meaning. Look at this conversation:
A: My mother said that it maysnow tomorrow. B: Really? It mightsnow?! That’s great! I couldmake a snowman or go for a “snow” walk. A: Don’t get too excited. If the temperature is high, it maynot snow. It mayrain. B: Well, I guess I could still go for a walk in the rain.
Be careful with may + “be” and “maybe”. Compare these sentences. Both are correct.
Ann is not here today. She may be sick. ➨ “may be” is a modal.
Ann is not here today. Maybe she is sick. ➨ “Maybe” is an adverb.
You can use must to say that you believe something is certain.
You have been travelling all day. You mustbe tired.
She mustget bored in her job: she does the same thing every day.
You use can't to say that you believe something is not possible.
You've just had lunch. You can'tbe hungry.
They haven't live here very long. They can'tknow many people.