A student of Abelard, John was one of the most learned of early medieval writers on moral and political matters. He was secretary to Theobald, archbishop of Canterbury, and to St Thomas à Becket, of whom he wrote a biography. From 1176 to 1180, he was bishop of Chartres. His two main works are the Polycraticus, a treatise on the principles of government, and the Metalogicus, a defence of logic showing considerable acquaintance with Aristotle.