Cinematic Believability

This is an argument that I’ve made several times, and I was surprised, as I went through my blog history, that I haven’t posted it before. Essentially, there are two ways to make fiction believable: realism and plausibility. Many people confuse these, but they are quite different: realism means that the story generally conforms to the nature of the “real world”–that is, no elements of fantasy. Plausibility means that, whether the story requires an initial suspension of disbelief or not, it progresses in a believable manner from it’s own viewpoint.
The movies that I generally use to contrast these elements are Pumpkinhead and I Know What You Did Last Summer. Both movies are about revenge taken on a bunch of teenagers after they cause drunken motor accidents–Pumpinhead then focuses on plausibility without realism, while I Know focuses on realism… without much plausibility.
In Pumpkinhead, a group of teens passing through a small rural town kill a small boy while racing their dirt bikes while drunk. The story then progresses unrealistically, as the father of the boy makes a pact with a local witch to send a “demon of vengeance” after the offenders. If one can suspend disbelief and accept that this happens within the world of the movie, the story then progresses both plausibly and interestingly.
I Know What You Did Last Summer begins similarly: a group of teens drinking and driving hit a Maine fisherman and then leave him for dead, attempting to hide the body by tying underwater. While this is a much more realistic scenario, for the story to progress we must then believe that the fisherman managed to hold his breath underwater–not only long enough to untie himself, but while unconscious. Said fisherman then waits a year, finally going on a rampage both sociopathic in nature and requiring superhuman strength.
While this approach may appeal to some viewers–and both of the above movies have their own “cult” followers–it is worth noting that the three biggest American horror franchises (Friday the 13th, Halloween, and Nightmare on Elm Street) all opted to forego realism.