Here is a theory that I have come up with:
There are 4 major parts of man: soul, spirit, astral body, and physical body.
When the man dies this is what happens to the parts in my POV:
Soul: goes to either heaven or hell
Spirit: Wanders the earth, these are the ghosts that are seen
Astral body: Reincarnates into another person
Physical Body: Lays in the ground until it is resurrected for the Final Judgement
Soul and Physical Body may be controversial, but without going into Christianity, give me your thoughts :)!