On a psychological level, one of the most severe effects of modern urban life in Campbell's work is paranoia. We have already seen Campbell's fascination with the complexities of human psychology in the tales of the Demons by Daylight period—tales that featured an intense, almost streamof- consciousness focusing upon a given character's mental state as he or she became insidiously enmeshed in the bizarre. In many cases, we learned, it was not immediately clear—and sometimes remained unclear to the end—whether the supernatural in fact came into play or whether the perceived anomalies were merely the result of an aberrant consciousness.

Campbell's later novels and tales in some senses follow and develop this pattern, but a significant proportion of them display characters whose extreme paranoia is itself the source of horror, with no supernaturalism even suggested. In recent decades many works of this kind have been written by various hands under the guise of horror fiction, but such a classification becomes problematical in many cases because these works so closely tread the borderline between horror and the mystery/suspense field, many times crossing over it. Many critics—H.P. Lovecraft among them—have maintained that the horror story must be supernatural, because only in this way can it convey the metaphysical fear that the universe itself has suddenly become an appallingly mysterious place, something far different from the mundane fear of being murdered or maimed that mystery/suspense fiction generates. If there are vampires; if people can rise from the dead; if there can be such an entity as Cthulhu or Glaaki—then it means that we have somehow misconstrued the true nature of the cosmos, and our place in it has now become tenuous indeed. Can the witnessing of even the most severe psychosis, and the crimes it may engender, achieve this level of metaphysical frisson? Clearly not; and yet, it would seem difficult—from Campbell's work alone, if not that of Ambrose Bierce, Robert Bloch (Psycho), and many others, going back even to some of Poe's tales (‘The Man of the Crowd’)—to exclude all nonsupernatural works of psychological suspense from consideration as horror tales.