What is genre theory a theory of? This paper argues that genre theory is an inquiry into the formation of fundamental categories of interpretation in history, where even the question of whether literary and rhetorical genres are in themselves fundamental is left open. Efforts to theorize genre are therefore beset by paradox since the categories that matter at any given time may not be literary or rhetorical genres. "Mauvais Genres" explores the paradox of genre through an analysis of the historical transition from a late Neoclassical poetics based upon genre to a modern system of philosophical aesthetics based upon trans-generic categories of the beautiful, the ugly, and the sublime, categories that fulfill the genre-function even as they marginalize genre as a means of classifying and evaluating texts. Principal figures are Locke, Shaftesbury, Hartley, Berkeley, Hume, Reynolds, and Baillie.