As described by the film aesthetician Charles Derry, the horror-of-the-demonic film suggested that the world was horrible because evil forces existed that were constantly undermining the quality of existence.
The evil forces could either remain mere spiritual presences, as in Don't Look Now (Nicolas Roeg, 1973), or they could take the guise of witches, demons, or devils.
Indeed, the idea of an evil incarnate has a long American tradition...
The themes of repression and evil forces have long been a staple of American literature, from Nathaniel Hawthorne's The House of Seven Gables and Washington Irving's "The Legend of Sleepy Hollow" to Edgar Allan Poe's 'The Raven' and Henry James' The Turn of the Screw.
Four themes that are common to these films lend a consistency to this genre.