本文從理論角度重新探索紀錄片的定義，並透過電影史回溯考察紀錄片與劇情片在美學與系譜學上的關係，進而討論「偽紀錄片」、「紀錄劇」、「反身性紀錄片」、「表白性的紀錄片」、「實驗紀錄片」，以至於21世紀大量出現的混雜了紀實與虛構元素的混血形式。本文的結論是：紀實的紀錄片與虛構的劇情片彼此的分野其實並非涇渭分明，兩者反而有很多共通處與相似的本質。因此，本文建議不要拘泥於討論甚麼是紀錄片、或紀錄片與劇情片的差異，而是用「紀實─虛構」、「論述─敘事」、「具象─抽象」三根軸線來考察個別影片的屬性，讓每部影片在此三根軸線所架構起來的三度空間中，都找得到各自特有的座標位置。

For more than a decade, hybrid forms in the documentary genre that mix documentary and fìction elements in one single fìlm had emerged and were endorsed in many documentary festivals around the world. It is, therefore, necessary to redefìne "what is documentary." This paper fìrst discusses the issue of redefìning documentary. It then traces back through the history of western, especially English, documentary film, to find out the fact that genealogically and aesthetically documentary had had an indisputablly close relationship with fiction film. This paper also discusses what counts as mock documentary, docudrama, reflexive documentary, performative documentary, experimental documentary, or hybrid forms that mix elements of documentary with those of fiction film. This paper concludes that it may be futile trying to distinguish between documentary and fìction fìlm. Instead, the paper proposes a 3-D model to indicate the relative position of each individual work within the space formed by the three axes - "fact-fìction, "exposition-narrative," and "representational-abstract".