Yes I'd agree that it is impossible to prove something to someone you don't share common ground with. I'll never be able to prove ghosts don't exist to someone

Yes I'd agree that it is impossible to prove something to someone you don't share common ground with. I'll never be able to prove ghosts don't exist to someone who believes they do. I might however be able to prove the absence of any evidence for the existence of ghosts, provided that the person I'm speaking to has the same perception of what constitutes evidence.