The study of the conventional dimensions of film, whether of characters, narrative device, material objects, locales, or thematic motifs, provides a means of examining the most fundamental cultural assumptions of American movie makers and movie audiences. Because plot conventions are, in themselves, indexes of cultural beliefs about the physical and social world and how they should function, scholarship that focuses on the birth, evolution, or obsolescence of individual plot conventions helps to reveal the interrelationship between the movement of popular film and changes in American society.