Horror, like action-thrillers, comedy and the tear-jerker, is one of those genres that takes its name from the emotional state is designed to arouse. Consequently, the key to understanding the genre of horror is to grasp the nature of the emotion that it is intended to engender.  This is how Aristotle proceeded in his analysis of tragedy, whose function he contended was to elicit pity and fear.  But to consider the philosophy of horror, we should begin by asking: what is the emotion that works of horror are supposed to provoke?

Perhaps the most straightforward approach to answering this question is to attempt to identify the object of the emotion of horror.  That is, what is horror directed at — what horrifies us in our response to works of horror?  An obvious answer is the monster: a creature of supernatural or scientific provenance, whether that's a demon, an alien, dinosaur, or even a haunted house or a malevolent car.

As a first approximation, we might define “a monster” as a being whose existence is denied by contemporary science.  This is a good start; it distinguishes the kind of characters in which we are interested from various other sorts of villains, like the Scorpio Killer in Dirty Harry. But, it is too broad, since it includes Superman and Peter Pan in the same category as Dracula and Pennywise the Clown.  And even if we are willing to label such benign creatures as monsters, they are not the sort of monsters that inhabit the genre of horror.