As a distinct genre, the film musical refers to movies that include singing and/or dancing as an important element and also involves the performance of song and/or dance by the main characters. Movies that include an occasional musical interlude, such as Dooley Wilson's famous rendition of "As Time Goes By" in Casablanca (1942), generally are not considered film musicals. By this definition neither would American Graffiti (1973), which, while featuring a continuous soundtrack of rock oldies coming from car radios in the nostalgic world of the story, has no performances by its ensemble cast.
The movie musical exploits more fully than any other genre the two basic elements of the film medium—movement and sound. In melodrama, although the characters' intense emotions are expressed through stylistic means ( mise-en-scène , lighting, music), their feelings are often repressed; by contrast, in film musicals characters are uninhibited and outwardly express emotion through song and dance. Gene Kelly's (1912–1996) famous refrain in Singin' in the Rain (1952), "Gotta dance," refers not only to his own inclination in that specific film but to the genre as a whole. Classical musicals depict a utopian integration of mental and physical life, of mind and body, where intangible feeling is given form as concrete yet gracious physical action. Whether the characters in musicals are feeling up or down, whether they are alone or in public, they are always able to fulfill their desire or to feel better by dancing or singing. In his influential discussion of entertainment, Richard Dyer cites the film musical specifically for its utopian sensibility, which he defines as its ability to present complex and unpleasant feelings in simple, direct, and vivid ways (Altman, 1981).
With the exception of some comedies, the musical is the only genre that violates the otherwise rigid tenets of classic narrative cinema. Just as Groucho Marx addresses some of his wisecracks directly to the camera, so characters sing and dance to the camera, for the benefit of the film viewer, rather than any ostensible audience within the film's story. As well, often the music accompanying singing stars conventionally comes from "no where"—outside the world of the film—another violation of the rules of realism that govern almost all other genres. The scene in Singin' in the Rain where Kelly adjusts the lighting and switches on a romantic wind machine on an empty soundstage to set the mood before proclaiming his love for Debbie Reynolds in the song "You Were Meant for Me," acknowledges the conventions of artificiality that characterize performance in musical films.