Eloquence is a central concern in rhetorical studies, with letter and word discordance (tanāfur) considered a defect that undermines eloquence. An examination of major Persian and Arabic rhetorical texts (3rd–14th century AH) reveals no clear criterion for identifying such discordance. This research aims to identify, classify, analyze, and critique the criteria for tanāfur in classical and contemporary rhetorical works and to propose a theoretical framework for organizing them. Using a descriptive-analytical method with a historical-critical approach, the study finds that dominant perspectives on tanāfur fall into four categories: (1) early views lacking definition or criterion; (2) emphasis on the “place of articulation”; (3) emphasis on the “correct linguistic intuition of native speakers”; and (4) use of “occurrence in the Qur’an” as a criterion. The first category is impressionistic; the fourth is theological and less effective in non-Muslim discourse. The second addresses the “creative aspect,” and the third addresses the “heuristic aspect” of discordance. Ultimately, the sound intuition and linguistic sense of authentic language users both generate and identify tanāfur. This intuition—shaped by historical, geographical, cultural, and biological factors (including oral and jaw structures)—remains the ultimate criterion. To render it more scientific, the objective features of “sound intuition” must be determined through formal and linguistic studies—an area overlooked by past and present scholars and therefore requiring further research.