One especially interesting concept.
When someone dies they are gone. Period.
But the people around them have trouble responding to that as rapidly. The person is alive in their minds.
My sister died 8 years ago. Every once in a while I catch myself thinking when I finish this or that I'll head over to her place. Or I'll hear something and think I'd like to share that with her.
And that being the origin of ghosts. I think once one accepts that "semi-ghost", sort of the concept that maybe they can still talk to dear old dead Dad it's easy to extrapolate ghosts into less personal situations.
Interesting guy.
Arf