'need not be the case' vs. 'not necessarily the case': Is there any difference? If so, what is it? Do they have the same meaning? Or do they differ in meaning? That's the main question actually. Should I conjugate certain -ly suffixes with just one of them (sentences) or for both? I'm inclined to say: "this theoretically need not(..)" and for the other "in theory this is not necessarily(..)". Which one would you use?