PMLA 126:1 (January 2011): 233-242 contains manifestos by Juan Boscán and Garcilaso de la Vega, introduced and translated by Anne Cruz and Elias Rivers.
Spain was the first European nation-state to appropriate Italian versification and prose style but also to dsiplace Italy from the political and literary spheres of power. The political and cultural significance of B and G’s revisionary poetics makes their prefaces (and these are prefaces) the first literary manifestos of early modern Spain.
The literary modernization of the Golden Age attended Spain’s formation as a modern state. It was the Venetian ambassador who suggested that B try Italian versification, which was fundamentally different from medieval Spanish abstract wordplay and rhymes. G followed, transforming Virgilian pastoral and Petrarchan lyrics into the endecasílabo in Castilian, that conveyed profound psychological insight.
From Italy G sent B a copy of Castiglione’s Courtier, urging him to translate it. It became a bestseller, with pirate editions too. And they wrote these prefaces to it, and to their own poetry; all of this is neglected by the world but note that it predates Ronsard by several decades. And these prefaces are the manifestos, and B and G knew they had launched a cultural revolution.