In A Companion to the Horror Film, a book compiled of essays, Harry M. Benshoff looks deeply at this question. Benshoff references Noel Carroll, who argues that a work of horror must include a monster. A monster in this case means a fearsome creature whose existence is not acknowledged by current science (in the realm of the story).
"Horror films not only include monsters, they are designed to arouse fear and disgust directed at a monster. The fearsomeness of the monster arouses fear," (Benshoff 5).
This combination of fear and disgust distinguishes horror from other genres.
This definition, however, seems to exclude too many central cases; there are more kinds of monsters than just the supernatural type. slashers being just one example. From this view, horroris a genre with two main subtypes: supernatural horror and realist horror.
The likelihood of creating a set definition for the genre rides on our ability to define what it is to be a monster, and because of this we are left without a true, set definition.
Fear and disgust are negative emotions, yet people go to see horror movies knowing that they will experience these negative emotions. If people avoid pain, why do they want to experience art that is painful (Benshoff)? How can audiences experience pleasure while reacting to fictional tragedy?
There are 5 theories that discuss this: control, compensation, conversion, and hedonic compensatory solution theory.
Control theorists believe the painfulness of art is mitigated by our ability to stop experiencing them at will.
Compensation theorists argue that painful reactions must be compensated by other pleasures - either in the craft of the narrative or in the awareness that we can sympathize with the suffering of others.
Conversion theorists believe that the overall experience is not painful, but instead pleasurable. The pain is converted into a larger, pleasurable experience.
Power theorists argue that we enjoy the feeling of power that arises from the realization of the endurance of humanity, or that we can overcome our fear.
The most popular theory, however, is the hedonic compensatory solution theory. This theory suggests that the bad feelings are overshadowed by the good, and that pleasure compensates for the pain.
In other words, fear and pain are the price we're willing to pay (Carroll) for the pleasure we experience while watching horror movies.
This view assumes that horror viewers are looking for pleasure, and that is the motivation.
However, the overall appeal of horror is still unexplained.
Do audiences feel genuine fear in response to horror films? The answer is yes.
Horror horrifies because we are capable of responding emotionally to imagined scenarios.
The thought theory suggests that emotions only require that we entertain or imagine that the events are taking place; We do not need to believe that anyone is in danger, we only need to imagine that that is the case.