This article examines the published work and correspondence of Martinho de Mendonça, a Portuguese philosopher and royal official known for writing on education and for serving the crown in Brazil. While recent scholarship has examined either Mendonça's contributions to philosophical inquiry in Portugal or his tenure as governor, here I analyze the constructions of authority forged in both his book on noble education and his administrative correspondence. Together, his published work and correspondence reveal the ways in which Mendonça's encounters with contemporary philosophy provided grounding for surmounting what he regarded as the historical obstacles to an ascendant royal authority in Portugal and its American empire.