Movie goers enter a theater, most likely they know what they can expect from the film they are about to see.
This is possible because films are put into categories or genres and viewers, knowledgeable of each genre and it's conventions, can deduce certain things about the movie they are about to see.
For instance, a Film Noir will feature a femme fatale, a hero who is not fully on the side of the law, and perhaps even a down ending.
As another example, a western is usually set in the American frontier and contains a hero or heroes who have to help bring order to a lawless town because of corruption.
Horror films are no different.
A view can expect a monster, even a spirit of something supernatural, chase sequences between the monster and victim, a final girl who will confront the monster in the climax, as well as canted angles and low key lighting all to put the viewer on edge.
John Carpenter's Halloween (1978) follows all of these conventions, but also, despite its low budget status, became so iconic that it established many conventions that were subsequently mimicked and even still used today.
Halloween is the story of demented killer Michael Meyers, who after being institutionalized for the killing of his sister, escapes and returns to his hometown to finish his killings.
He is pursued by Dr.
Sam Loomis from the hospital, who on a huntch that Michael is headed home to Haddonfield.
There Michael finds a new crop of victims, teenage babysitters.
Halloween fulfills all of horror's most basic conventions already mentioned above.
The most obvious is the films use of the monster.
Unlike a film like Alien (Ridley Scott 1979), or King Kong ( Merrian Cooper and Ernest Schoedsack, 1933), the monster in Halloween is human, albeit a masked psychopathic murderer.
The monster takes the form of Michael Meyers, a young boy at the beginning of the film, who viciously murders his sister in cold blood.
The scene and film open with a point of view shot, showing Michael's vision as he watches his sister with her boyfriend from outside the house.
The camera continues to stay with Michaels point of view as he enters the house through the back door and takes a butcher knife out of the kitchen drawer.
He proceeds to walk up the stairs, picking up a Halloween mask on the way, enters his sisters bedroom where she is topless.
He walks over to her, and, although it is no surprise to the audience because of the use of dramatic irony, stabs her repeatedly much to her surprise.
Later, when Michael escapes from his mental institution, he acquires another mask, thus, establishing a genre convention of its own, the masked killer, which is mimicked in several subsequent horror films, including the Friday the 13th series.
The chase scene in Halloween is saved for the climax, when Michael finally chooses Lori as his victim.
Lori, who has gone to the house which Annie was babysitting to investigate.
As she discovers the bodies of her murdered friends, Michael, appears behind her, slicing her arm and sending her down the stairs.
The sequence continues as Lori runs into the street, and back to where she left the children she was babysitting.
Michael follows her there, where he is ultimately shot by Dr.
Loomis.
This indicates another convention, the undying, almost supernatural killer.
Again, this convention is repeated in the Friday the 13th series starting with the second installment.