 John of Salisbury (1115/20–1180) was among the foremost philosophers of the so-called twelfth century Renaissance, contributing to the development of political and moral philosophy as well as to the medieval theory of education and to the dissemination of emerging Aristotelian learning. Having received an extensive education in Paris, he spent most of his life as an active servant of the church. An associate of Archbishop Thomas Becket of Canterbury during his dispute with King Henry II of England, John eventually was raised to the office of Bishop of Chartres. John’s thought has been characterized as “humanistic”, since he valorizes the dignity of humanity and of nature generally: The latter is intelligible and may be understood through the application of natural reason. Yet John admitted that severe impediments exist to the attainment of wisdom. Throughout his writings, he professed to follow the moderate skepticism of Cicero and the New Academy, which rejected dogmatic claims to certainty. The best that rational human inquiry may in most matters achieve, John says, is probable truth, always subject to re-evaluation and revision. The general tenor of his philosophy is reflected in his advocacy of moderation and his emphasis on nature as a normative guide to earthly fulfillment. John composed several treatises of philosophical interest, most notably the Policraticus (PC), but also the Metalogicon (ML) and the Entheticus de dogmate philosophorum (EMM). These works were all completed between 1154 and 1159, during the period of John’s service to Archbishop Theobald, Becket’s predecessor at the see of Canterbury. John’s other writings—two letter collections, two hagiographies, and a history—evince the practical application of his philosophical commitments.