Why is it difficult to define nonfictional prose as one genre?

Defining nonfictional prose as a single, unified genre is considered an immensely challenging task because the category is inordinately vast, variegated, and lacks a singular characterization.12

Several factors contribute to this difficulty:

• Prodigious Variety: Nonfictional prose covers an almost infinite range of themes and assumes many different shapes, including political, religious, philosophical, and biographical writings. It encompasses any literary work based primarily on fact, yet it remains flexible enough to incorporate fictional elements.231
• Lack of Stylistic Uniformity: Unlike fiction, which often demands a specific craft or sense of inevitability, nonfictional prose employs diverse styles—ranging from casual, rambling reflections to highly rhetorical, musical prose—depending on the author's intent and cultural context.43
• Blurring Boundaries: The line between nonfictional prose and fiction is often tenuous. Introspective works, such as diaries, journals, and autobiographies, frequently share structural and thematic commonalities with the novel, making strict categorization difficult.3
• Functional Diversity: The genre serves many purposes, including instructing, persuading, converting, or conveying reality, which prevents it from being reduced to a single, rigid definition.1

Ultimately, any attempt to define it as a unitary genre risks being a limitation that excludes its essential nature.2