Abstract
Canon law began as sets of norms for the regulation of Christian conduct in the world and the relations of Christians with each other. These were based on principles derived from scripture, the influence of respected teachers such as St. Paul, the decisions of ecclesiastical assemblies called synods or councils, and papal decretals. These norms were called canons, rather than laws. The term canon translates the Greek κανών, meaning a carpenter’s straight-edge and, by extension, a guide or rule. Decretals, or letters, were responses of the pope to questions posed to him regarding Church doctrine. While relevant only to that particular circumstance, papal decretals, over time, came to be regarded as binding for all of Christendom. Church councils sought to standardize doctrine, liturgy, and legal norms by the collective decisions of assembled bishops, but regional ecclesiastical identities endured, particularly in the person of the independent local bishop governing his own church with its own customs, in the increasing distinction between clergy and laity, and in the development of a clerical hierarchy. Regional and local councils, presided over by bishops, could either adapt or repeat canons issued at ecumenical councils depending upon the needs. Collections of canons, always privately compiled—until the Liber Extra Decretalium of Pope Gregory IX (r. 1227–1241) in 1234—and adopted for use by regional churches, were arranged either chronologically according to the assumed dates of their texts or systematically according to topics treated. The Greek Christian church adopted the term nomocanon to designate its canons that were approved by the Byzantine emperor and thereby became νομοι, laws. The Latin Christian church called its laws ius canonicum as a parallel, but not dependent, legal system to the study of Roman law. The shift from collections of texts to a legal science—whereby one went to Bologna or Paris, for example, for the specific purpose of studying law—occurred during the classical period, from shortly before 1140 to 1375, beginning with the almost universal adoption of the work of the canonist Gratian, the Decretum. During this period—frequently referred to as the classical period—the doctrine of papal judicial supremacy emerged, and papal legal decisions became the primary source of canon law. In the law books produced during the classical period, canon law acquired a form and structured that remained in effect in the Roman Catholic Church until 1917–1918. Parts of it were adopted in other Christian confessions from the 16th century.