Cinematic dialogue is oral speech between fictional characters. This distinguishes dialogue from other types of cinematic language such as voice-over narration, internal monologue, or documentary interviews, which have different characteristics.
Since the birth of the cinema, it has been said that "film is a visual medium." Supposedly, films must tell their stories visually—editing, deep focus, lighting, camera movement, and nifty special effects are what really count. Dialogue, on the other hand, is just something we have to put up with. Even the term "film viewing" does not take into account the role of dialogue. We are accustomed to the analogy of the filmgoer as voyeur, surreptitiously spying on the actions of the on-screen characters. Yet what is overlooked is that viewers are also auditors. In fact, they are eavesdroppers, listening in on conversations purportedly addressed to others, but conversations that—in reality—are designed to communicate vital information to the listeners in the dark.
Dialogue, by its very nature, is deceptive. The characters on the screen speak not from their hearts but from a script; they whisper secrets to a vast public; they speak to inform the audience, not each other. Watching a film, on one level we are conscious of this duplicity, but on another we willingly suspend disbelief. Dialogue that betrays its true address to the moviegoer or sounds implausible is often condemned as clumsy because it fractures this fictional compact. But sometimes screenwriters intentionally use dialogue to wink at the audience, as in Scream (1996), when one of the characters says: "Oh, please don't kill me, Mr. Ghostface, I wanna be in the sequel!" Moreover, who is to say what is "out of character" for a fictional character? In Hollywood Shuffle (1987) Robert Townsend asks us to reconsider our expectations about what is "true to life" when he presents an African American actor speaking in a stereotypical black dialect and then reveals the actor's actual speaking voice to be British and very cultured. Thus, all of the rules about dialogue usage offered by screenwriting handbooks should be viewed skeptically, as any rule may be violated for calculated effect.