In The Dialogic Imagination, Bakhtin argues that the novel is a polyphonic form with a multitude of competing voices and competing opinions. It is fundamentally different from the epic, which is univocal and offers one unified perspective on the world. The epic is an elite, aristocratic form while the novel is a democratic form that levels hierarchy by giving characters from all classes a voice.
Parody is inherently dialogic or multi-vocal because it imitates an author or a style of writing for comic or mocking effect. It involves at least two different voices: the voice of the original model and the parodying voice, which enters into an implicit dialogue with the original voice. Parody is a type of genre that Bakhtin called "double voiced."
Parody also arises in situations of heteroglossia (many voices), where a society is vibrantly full of many competing voices and discourses. Parody, for example, could not thrive (except underground) in a totalitarian regime in which no mockery of the official language of policy would be tolerated.
Parody does not need all the sophisticated apparatus of the novel form but the novel, according to Bakhtin, arises from the same soil as parody: both are anti-authoritarian forms of discourse meant to provide alternative points of view that challenge or question ruling class ideology.