Fantasy and sf can dramatize speculative answers to philosophical questions like:
Are ghosts real?
If so, what are they like?
What would it be like to be one?
Are reported apparitions really visible departed souls?
Surely spirits, if they exist, are invisible?
Surely disembodied consciousness is not embodied?
Are apparitions mere after-images or mirages?
Alan Moore's Jerusalem answers the second and third questions. Michael not only theorizes that ghosts hang around at night because they can see well in the dark but also begins to experience this with his own ghostly vision.