" Photius even went so far as to propound a new and deeply heretical theory that he had just thought up, according to which man possessed two separate souls, one liable to error, the other infallible. His dazzling reputation as an intellectual ensured that he was taken seriously by many—including, of course, Ignatius, who should have known better; and after his doctrine had its desired effect by making the patriarch look thoroughly silly he had cheerfully withdrawn it. It was perhaps the only completely satisfactory practical joke in the history of theology, and for that alone Photius deserves our gratitude. "

― John Julius Norwich , Absolute Monarchs: A History of the Papacy