What is a ghost? It is a memory without a body, a memory made of nothing. In our universe, living matter forms a memory. Dead matter doesn't do anything. A rock, for example, only moves when the wind moves it, rolls when water pressures it. But something that lives purposely maintains its form and features through time. Life is the moving image of eternity. When I see a person for the first time after many years, all the matter that made up their body when I last saw them has been replaced. On the level of stuff, they are a different person, but at the level of appearance, they are the same person. Life is matter remembering the past.
A ghost is supernatural because in our universe, memories are only natural. What is ghostly is what appears to be disembodied. This is why ghosts love to appear in windows; they understandably relate with the reflections of the living: the image without the body, soul without substance, memory without meat. Indeed, the most terrifying moment in Henry James's The Turn of the Screw, which was published two years before the close of the last haunted century of humankind, the 19th century (ghosts became extinct at the dawn of the 20th century), is when the governess of two orphaned children, Miles and Flora, finally confronts one of the two ghosts that she has seen on the grounds of her employer's country estate. It appears in the window: "The next thing I saw was that, from outside, he had reached the window, and then I knew that, close to the glass and glaring in through it, he offered once more to the room his white face of damnation."
The ghost stares at her and the boy, who is in her arms and has his back turned to it. "I kept my eyes on the thing at the window and saw it move and shift its posture," she says. The ghost badly wants the boy, but she protects him by keeping his eyes away from the window.
It was like fighting with a demon for a human soul, and when I had fairly so appraised it I saw how the human soul—held out, in the tremor of my hands, at arm's length—had a perfect dew of sweat on a lovely childish forehead. The face that was close to mine was as white as the face against the glass, and out of it presently came a sound, not low nor weak, but as if from much further away, that I drank like a waft of fragrance.
Eventually, the very physical boy gives up the ghost. He expires in her arms, and matter stops remembering him.
We also find this connection between reflections and ghosts in some of the ancient Japanese stories collected in Kwaidan: Stories and Studies of Strange Things, a book by one of the most curious literary figures of the 19th century, Lafcadio Hearn. For example, in "Of a Mirror and a Bell," a young farmer's wife donates a little mirror to a local temple. This is apparently the thing to do. All of the women in her village are donating mirrors to the temple, which is raising money for a bell. But soon after the farmer's wife hands the mirror to a priest, she remembers that it has a deep history in her family. Its surface has reflected the face of her mother, her grandmother, her great-grandmother. The farmer's wife starts longing for the return of the mirror; she thinks about it night and day. She considers buying it back from the temple but doesn't have enough money. She thinks about stealing it but hasn't got the guts. Writes Hearn:
She became very unhappy—felt as if she had foolishly given away a part of her life. She thought about the old saying that a mirror is the Soul of a Woman—(a saying mystically expressed by the Chinese character for Soul, upon the backs of many bronze mirrors)—and she feared that it was true in weirder ways than she had before imagined.
Eventually, a priest discovers her deep love for the mirror and chastises her for desiring something that she has given as a religious gift. She kills herself, after promising to return as a ghost.
But many of the stories in Kwaidan, and other collections by Hearn, are not about mirrors or reflections but the beauty of ghosts. Whenever a young man encounters an extraordinarily beautiful woman in a story, that woman is certainly a ghost. The samurai in "The Story of Aoyagi":
Tomotada... deemed himself lucky to be waited upon by so comely a maiden. He could not turn his eyes away from her—though he saw that his admiring gaze made her blush;—and he left the wine and food untasted before him.
The maiden turns out to be not only a ghost but also the spirit of a tree. What is this correlation between beauty and apparitions telling us? It links the transience of beauty with the transience of our existence. Because life is so brief, and because it is itself an image composed of lifeless matter (matter that enters, shapes the image, and departs), it is ghostly.