This is probably most evident in the modern treatment of vampires. The two most important things to remember about vampires are
- vampires are dead, and
- vampires are demon-possessed.
As another example, take pretty much anything written by H.P. Lovecraft, who seems to appeal chiefly to boys between 12 and 21. His ideas for horror seem to boil down to the following:
- Big is scary.
- Old is scary.
- Tentacles are scary.
- Big words from the thesaurus are scary.
Fortunately, there are good stories out there, too. Some of the best come from M.R. James, who had precisely the knowledge of ancient and medieval religious beliefs, writings, and practices to give his stories a proper depth. So when the villain in "Lost Hearts" writes a reference in his diary about the purported magical practices of Simon Magus as recounted in the so-called Recognitions of Clement, it is a bit creepy to discover that there really is such a book and that it says exactly what is quoted in the story. Also, as is conceded in the story, this book, though of ancient origin, is not a genuine work of Pope St. Clement.
Another excellent writer of ghost stories had his own interesting story to account for the learning evident in his writings. Robert Hugh Benson was the son of an Archbishop of Canterbury; after his father's death, he converted to the Catholic Church and became a priest, then a monsignor. His book The Necromancers is an excellent warning against the Spiritualism of his day and the "ghost hunting" of our own.
Perhaps my favorite work of his pertaining to ghost stories is A Mirror of Shalott, which begins with an instructive philosophical argument between several priests, some of whom were entirely skeptical that ghostly appearances occurred as in popular tales, and others of whom were more accepting. They agreed, however, that each evening one of them would recount some odd event from his own experience. In fact, I suspect that these are indeed fictionalized versions of accounts Msgr. Benson heard firsthand; something like one of them happened separately to a friend and to me.
An important thing to remember is that a proper ghost story is always a morality tale. Usually, the ghost appears to exact punishment on someone for a serious offense, which may be murder, greed, inappropriate curiosity, dabbling in sorcery, or something similar.