Notwithstanding its value as the earliest extant New Persian treatment of the art of rhetoric, Rādūyānī's Interpreter of Rhetoric (Tarjumān al-Balāgha) has yet to be read from the vantage point of comparative poetics. Composed in the Ferghana region of modern Central Asia between the end of the eleventh century and the beginning of the twelfth century, Rādūyānī's vernacularization of classical Arabic norms inaugurated literary theory in the New Persian language. I argue here that Rādūyānī's vernacularization is most consequential with respect to its transformation of the classical Arabic tropes of metaphor (istiʿāra) and comparison (tashbīh) to suit the new exigencies of a New Persian literary culture. In reversing the relation between metaphor and comparison enshrined in Arabic aesthetics, Rādūyānī concretized the Persian contribution to the global study of literary form.