Expository films rely on the narration to drive the story or carry the plot, and use images as supportive elements. Generally these films are written out in script form first, like one would do with a fiction film, and then the voice over is recorded, while accompanying images are sought to either illustrate or counterpoint the narrator. This is called evidentiary editing, the seeking imagery that reinforces the claims of the narrator. The expository film draws on the long history of rhetoric and the art of persuasion, allowing the narrator to make claims, and then presenting evidence to back up those claims, appealing to the common sense of the audience. The narration, delivered in a detached and above-the-fray kind of way, presupposes its own authority, and at the time, audiences had enough faith in the government and the establishment to believe it.
– from the upcoming book “How to Film the Truth: The Story of Documentary Film As a Spiritual Journey” to be released in the Summer of 2018 by Wipf & Stock