Documentary exploits the camera's affinity for recording the surface of things, what the realist film theorist Siegfried Kracauer called the "affinity" of film as a photographic medium for capturing "life in the raw." Even before the invention of motion pictures, photographers of the nineteenth century, such as Eadweard Muybridge (1830–1904), with his "animal locomotion" series, demonstrated the extent to which the camera might reveal facts and details of the world to us that we could not perceive with the naked eye.
Documentary images are different from fiction precisely because they possess an indexical bond, a referent, to the historical real. Thus documentaries are unique in engaging what the documentary theorist Bill Nichols calls our epistephilia, a pleasure in knowing about the real world. At the same time, however, no matter how marvelous the special effects in a fiction film, a death scene will never produce the same kind of horror as that generated by, say, the Zapruder footage of President John F. Kennedy being assassinated or the explosion of the space shuttle Challenger as caught by television news cameras. Therefore, documentary film has the power to bring about change in the audience, whether to influence attitudes, increase understanding, or persuade to action, and for this reason documentary film has frequently been used for propaganda purposes, both overtly and subtly.
John Grierson (1898–1972), the filmmaker, producer, and advocate who spearheaded the British documentary movement in the 1920s, coined the term "documentary" in a review of Robert Flaherty's Moana (1926). The film, he wrote, "being a visual account of events in the daily life of a Polynesian youth and his family, has documentary value" because the camera captured and revealed truths about Polynesian culture (Hardy, p. 11). Although later on such assertions would be challenged as First World privilege and presumption, for filmmakers of Grierson's generation the relation of the camera to the profilmic event was for the most part unproblematic.
Because of the wide stylistic diversity of films commonly categorized as nonfiction, documentary has been notoriously difficult to define. In seeking to be inclusive, inevitably most definitions have been vague, clumsy, and prescriptive. As Nichols observes, "Documentary as a concept or practice occupies no fixed territory. It mobilizes no finite inventory of techniques, addresses no set number of issues, and adopts no completely known taxonomy of forms, styles, or modes" (p. 12). Clearly documentary cannot be understood as a genre in any sense equivalent to the genres of commercial fiction cinema; yet whatever the style of individual documentary films, all documentaries make truth claims about the real world. Perhaps the most useful definition, then, is the one offered by Grierson: the "creative treatment of actuality." It not only has the virtue of brevity, but also incorporates both documentary's connection to the real world ("actuality") and the filmmaker's inevitable shaping influence ("creative treatment"). Of course, the perennial problem, for documentary filmmakers as well as critics and audiences, has been to negotiate a proper balance between the two.