Every documentary depends on its viewers believing its premise. The illusion of believability is most often either confirmed or destroyed by the credits. Frequently the audience first learns the people on the screen were actors, and that they have fallen prey to the thick veil of believability that documentary films are so able to portray.
To capture the audiences trust directors of documentary films apply many of the tactics and conventions documentaries serve to leave the audience questioning the reality and believability of what they view in the theatre and at home. Documentaries inspire an awareness of being that one has not previously experienced.
The film urges the spectator to reevaluate not only one's breadth of knowledge but also puts forward the message that the documentary is actually made to talk about and the real truth from a person who is not involved with the message. Documentary film is a broad category of visual expression that is based on the attempt, in one fashion or another, to "document" reality.
Although "documentary film" originally referred to movies shot on film stock, it has subsequently expanded to include video and digital productions that can be either direct-to-video or made for a television series. Documentary, as it applies here, works to identify a "filmmaking practice, a cinematic tradition, and mode of audience reception" that is continually evolving and is without clear boundaries.
The nature of documentary films has changed in the past 20 years from the cinema verity tradition. Landmark films such as The Thin Blue Line by Errol Morris