A central feature of the narrative authority El Inca Garcilaso de la Vega constructs for himself in the Comentarios reales is his linguistic knowledge. As a native speaker of Quechua, Garcilaso is able to act as an interpreter—that is, a lengua—between the Andean and Spanish traditions to which he is heir. This article analyzes the forging of this authority in the first two works published by Garcilaso: his translation of the Dialoghi d'amore by Leone Ebreo (1590) and his history of the expedition led by Hernando de Soto to La Florida (1605). Although they pertain to very distinct genres, both of these works consider the nature and capacities of lenguas (the tongue, the interpreter), especially in relation to the eye. While in both philosophical and historiographical terms, the eye is the privileged organ, Garcilaso subtly refines this corporeal hierarchy and begins to shape the authoritative tongue that will become crucial in his later works.