This article investigates the stylistic and linguistic features of Gustave Flaubert’s prose, with a particular focus on lexical contradiction and idiomatic tension. Through a close analysis of key works such as Madame Bovary, L’Éducation sentimentale, and Bouvard et Pécuchet, the study highlights how Flaubert’s writing systematically juxtaposes opposing semantic registers—romantic idealism and mundane realism, poetic elevation and trivial detail. These lexical contradictions not only enrich narrative depth but also underscore the disillusionment and irony characteristic of Flaubert’s modern vision.The article further explores how Flaubert manipulates idiomatic expressions, either by subtly distorting them or by integrating them ironically into character discourse. This tension between conventional language and authorial critique reveals Flaubert’s ambivalent relationship with linguistic norms and his pursuit of lemot juste. Drawing on French and Francophone critical literature, the study situates Flaubert’s stylistic innovation within broader debates about the literary function of cliché, the evolution of free indirect discourse, and the modern fragmentation of narrative voice.By analyzing the paradoxes at the heart of Flaubert’s style, the article demonstrates how lexical contradiction and idiomatic tension function not only as aesthetic devices but also as means of epistemological inquiry—interrogating language,meaning, and the act of writing itself.