Canon-law collections
John's lasting contribution was his reorganization of the Church's canons. Departing from the chronological arrangement of earlier collections, he grouped the canons according to their subject matter on a philosophical principle, reducing the number of organizational categories from sixty to fifty. The result, his Synagoge or collection in fifty titles, became a foundational text of Byzantine canon law.
His compilation gathered the canons of seven councils — Nicaea, Ancyra, Neocaesarea, Gangra, Antioch, Ephesus, and Constantinople — together with the Apostolic Canons, the canons of Sardica, and the canonical letter of Basil the Great. After his arrival in Constantinople he produced a further work, an abridgment of his collection to which he added a comparison of the imperial rescripts and civil laws bearing on the Church, an early form of the nomocanon that combined ecclesiastical canons with civil legislation.
These collections exercised a long influence: the later and more famous Nomocanon associated with Photius the Great drew upon John's work.