She [Madame Bovary] had that indefinable beauty that comes from happiness, enthusiasm, success—a beauty that is nothing more or less than a harmony of temperament and circumstances.

In this description of Emma Bovary, Flaubert suggests that what observers call “beauty” can be a social and psychological effect rather than a fixed physical trait. The “indefinable” quality arises when inner disposition (temperament) aligns with outward conditions (circumstances): happiness, excitement, and the sense of being favored by life create an aura that reads as attractiveness. The line also hints at the fragility of such beauty—if it depends on success and enthusiasm, it can fade as quickly as fortunes or feelings change. In the novel’s larger critique of romantic illusion and bourgeois aspiration, the remark underscores how Emma’s self-presentation and perceived charm are bound up with her shifting fantasies and satisfactions.