Book excerpt: A study of John Trevisa's rhetorical arguments for the value, necessity, and authority of translation in his English 'Polychronicon'. John Trevisa was one of the most prodigious translators living in England in the fourteenth century. His numerous translations of works from Latin into English helped to ensure the creation and perpetuation of late-medieval vernacular history, literature, and culture in Britain. His translation of the 'Polychronicon', a universal history of the world originally compiled byRanulf Higden, is both his magnum opus and his opportunity to present rhetorical arguments for the value, necessity, and authority of translation. Through his paratextual 'Dialogue between a Lord and a Clerk on Translation' and prefatory letter to Lord Thomas Berkeley as well as his intertextual explanatory notes to the 'Polychronicon', John Trevisa explores the tasks of the translator.