You may go there: I don’t mind.
You can go there: it is quite near.
You cannot go there: you don’t know the address.
You need not go there: I can ring them up.
You must not go there: they are very bad people.
You need not have gone there yesterday.
You should go there: they are waiting for you.
You should have gone there yesterday.
You should not have gone there yesterday.
She must be at home now.
She must have been at home yesterday.
We may come to see you tomorrow.
They may have come to our place, but we were out.
He must have seen this monument when he was in your town.
He may have seen this monument when he was in your town.
He can’t know this picture.
He can’t have seen this picture.
He might know the problem, so he might know the answer to this question, but I am not very sure (not quite sure).
Where are they living? — They might be living abroad, but I am not so sure of it.
You must be asking for trouble.
You should listen to him and try not to worry about it.