This chapter attempts to define ‘films of presumptive assertion’. This is the proposed label for the field of film studies that has been typically labeled as documentary and non-fiction. The chapter further labels the analysis of films of presumptive assertion in stages by drawing a distinction between fiction and non-fiction. Then it exploits what has been said about it. The chapter goes further by proposing an analysis of films of presumptive assertion as a subcategory of the non-fiction film. Finally, the chapter contemplates a series of problems and questions that the proposed theory is likely to raise. The chapter claims that this concept, presumptive assertion, captures what people mean to talk about when they speak informally of documentaries and non-fiction films.