They are generally given in answer to consultations, but are sometimes due to the initiative of the popes. These furnish, with the canons of the councils, the chief source of the legislation of the church, and formed the greater part of the Corpus Iuris Canonici before they were formally replaced by the Codex Iuris Canonici of 1917. However, Cardinal Pietro Gasparri led the papal commission for the revision of canon law and later on published a guide to the fonts used in the 1917 code, many canons in this code can easily be retraced in their relationship to and dependency on medieval decretals as well as Roman law.
In themselves the medieval decretals form a very special source which throws light on medieval conflicts and the approaches to their solution. They are sometimes concerned with very important issues touching on many aspects of medieval life, for example marriage and legal procedure.
In a narrower sense it denotes a decision on a matter of discipline.
In the strictest sense of the word, it means a papal rescript (rescriptum), i. e. an answer of the pope when he has been appealed to or his advice has been sought on a matter of discipline.
Papal decretals are therefore not necessarily general laws of the Church, but frequently the pope ordered the recipient of his letter to communicate the papal answer to the ecclesiastical authorities of the district to which he belonged; and it was their duty then to act in conformity with that decree when analogous cases arose. It is generally stated that the most ancient decretal is the letter of Pope Saint Siricius (384-398) to Himerius, Bishop of Tarragona in Spain, dating from 385; but it would seem that the document of the fourth century known as "Canones Romanorum ad Gallos episcopos" is simply an epistola decretalis of his predecessor, Pope Damasus (366-384), addressed to the bishops of Gaul (Babut, La plus ancienne décrétale, Paris, 1904). The decretals ought to be carefully distinguished from the canons of the councils; from the epistol dogmatic, i. e. the pontifical documents touching on Catholic doctrine; from the constitutiones, or pontifical documents given motu proprio, i.e. documents issued by the pope without his being asked to do so or consulted upon a subject.
Finally, under the name decretals are known certain collections, containing especially, but not exclusively, pontifical decretals. These are the canonical collections of a later date than the "Decretum" of Gratian (about 1150). The commentators on these collections are named decretalists, in contradistinction to the decretists, or those who commented upon the "Decretum" of Gratian. Eventually some of these collections received official recognition; they form what is now known as the "Corpus Juris Canonici". An account follows of the collections of decretals, particularly of those of Gregory IX.
Pope Gregory IX commissioned the Dominican Raymund of Peñafort to edit a comprehensive collection of papal decretals. This collection of nearly 2000 decretals appeared in 1234 as the Decretales Gregorii IX, also known as the Liber Extra, which was also immediately send to the universities of Bologna and Paris. In 1298 pope Boniface VIII published the next major collection of decretals. He entrusted three canonists with its redaction. This collection is known as the Liber Sextus. In the fourteenth century a few small collections followed: the Constitutiones Clementinae or Clementines (1317), edited by Anastasius Germonius and published by pope John XXII, and the Extravagantes Johannes XXII (1325-1327).
The second compilation, also called "Decretales mediæ" or "Decretales intermediæ", was the work of a private individual, the Englishman John of Wales (Johannes de Walesio, Walensis or Galensis). About 1216 an unknown writer formed the "Compilatio quarta", the fourth collection, containing the decretals of the pontificate of Innocent III which are of a later date than 7 January, 1210 and the canons of the Fourth Lateran Council held in 1215. Finally, the fifth compilation is, like the third, an official code, compiled by order of Honorius III (1216-1227) and approved by this pope in the Bull "Novæ causarumn" (1226 or 1227). It must also be noted that several of these collections contain decretals anterior to the time of Gratian, but not inserted by him in the "Decretum". Bernard of Pavia divided his collection into five books arranged in titles and chapters. The first book treats of persons possessing jurisdiction (judex), the second of the civil legal processes (judicium), the third of clerics and regulars (clerus), the fourth of marriage (connubium), the fifth of delinquencies and of criminal procedure (crimen). In the four other collections the same logical division of the subject-matter was adopted. (For the text see Friedberg, Quinque compilationes antiquæ, Leipzig, 1882.)
St. Raymond executed the work in about four years, and followed in it the method of the aforesaid "Quinque compilationes antiquæ". He borrowed from them the order of the subject-matter, the division into five books, of the books into titles and of the titles into chapters. Of the 1971 chapters which the Decretals of Gregory IX contain, 1771 are taken from the "Quinque compilationes antiquæ", 191 are due to Gregory IX himself, seven are taken from decretals of Innocent III not inserted in the former collections, and two are of unknown origin. They are arranged, as a general rule, according to the order of the ancient collections, i. e. each title opens with the chapters of the first collection, followed by those of the second, and so on in regular order; then come those of Innocent III and finally those of Gregory IX. Almost all the rubrics, or headings of the titles, have also been borrowed from these collections, but several have been modified as regards detail. This method considerably lightened St. Raymond's task. However, he did more than simply compile the documents of former collections. He left out 383 decisions, modified several others, omitted parts when he considered it prudent to do so, filled up the gaps, and to render his collection complete and concordant, cleared up doubtful points of the ancient ecclesiastical law by adding some new decretals. He indicated by the words et infra the passages excised by him in the former collections. They are called partes decis . The new compilation bore no special title, but was called "Decretales Gregorii IX" or sometimes "Compilatio sexta", i. e. the sixth collection with reference to the "Quinque compilationes antiquæ". It was also called "Collectio seu liber extra", i. e. the collection of the laws not contained (vagantes extra) in the "Decretum" of Gratian. Hence the custom of denoting this collection by the letter X (i.e. extra, here not the Roman numeral for ten).
Quotations from this collection are made by indicating the number of the chapter, the name the work goes by (X), the number of the book, and that of the title. Usually the heading of the title and sometimes the first words of the chapter are quoted; for instance, "c. 3, X, III, 23", or "c. Odoardus, X, De solutionibus, HI, 23", refers to the third chapter, commencing with the word Odoardus, in the Decretals of Gregory IX, book III, title 23, which is entitled "De solutionibus". If the number of the chapter or of the title is not indicated it will easily be learned on consulting the alphabetical indexes of the rubrics and of the introductory words of the chapters, which are to be found in all editions of the "Corpus Juris Canonici". Gregory IX sent this new collection to the Universities of Bologna and Paris, and declared, by the Bull "Rex pacificus" of 5 September, 1234, that this compilation was the official code of the canon law. All its decisions have the force of canon law whether they be authentic or not, whatever the juridical value of the texts considered in themselves, and whatsoever the original text. It is a unique collection; all its decisions were simultaneously promulgated, and are equally obligatory, even if they appear to contain, or if in fact they do contain, antinomies, i. e. contradictions. In this peculiar case it is not possible to overcome the difficulty by recourse to the principle that a law of later date abrogates that of an earlier period. Finally, it is an exclusive collection, i.e. it abrogates all the collections, even the official ones, of a later date than the "Decretum" of Gratian. Some authors (Schulte, Launin) maintain that Gregory IX abrogated even those laws prior to Gratian's time which the latter had not included in his "Decretum", but this opinion is contested by several others (von Scherer, Schneider, Franz Xavier Wernz, etc.). The controversy is no longer of practical interest.
The Decretals of Gregory IX differ widely from modern codes. Instead of containing in one concise statement a legislative decision, they generally start with an account of a controversy, the allegations of the parties in dispute, and a demand or the solution of the question; this species facti or the pars historica has no juridical value whatever. The enacting part of the chapter (pars dispositiva) alone has the force of law; it contains the solution of the case or the statement of the rule of conduct. The rubrics of the titles have the force of law when their sense is complete, as for instance, Ne sede vacante aliquid innovetur (Let there be no innovation while the see is vacant), because the headings form an integral part of the official code of the laws. However, they ought always to be interpreted according to the decisions contained in the chapters. The historical indications concerning each chapter are often far from being exact, even since they were corrected in the Roman edition of 1582. It may be regretted that St. Raymond did not have recourse to the original documents themselves, of which a large number must have been at his disposal. The summaries (summaria) which precede the chapters are the work of the canonists and may assist in the elucidation of the text. The partes decis are sometimes of like use, but never when these parts were designedly omitted from a desire to extinguish their legal force or because they contain decisions irreconcilable with the actual text of the law.
Like the former canonical collections, the Decretals of Gregory IX were soon glossed. It was customary to add to the manuscript copies textual explanations written between the lines (glossa interlinearis) and on the margin of the page (glossa marginalis). Explanations of the subject-matter were also added. The most ancient glossarist of the Decretals of Gregory IX is Vincent of Spain; then follow Godefridus de Trano (died 1245), Bonaguida Aretinus (thirteenth century) and Bernard of Botone or Parmensis (died 1263), the author of the "Glossa ordinaria", i. e. of that gloss to which authoritative credence was generally given. At a later date some extracts were added to the "Glossa ordinaria" from the "Novella sive commentarius in decretales epistolas Gregorii IX" by Giovanni d'Andrea (Johannes Andreæ). After the invention of printing, the Decretals of Gregory IX were first published at Strasburg from the press of Heinrich Eggesteyn. Among the numerous editions which followed special mention must be made of that published in 1582, in dibus populi romani, by order of Gregory XIII. The text of this edition, revised by the Correctores Romani, a pontifical commission established for the revision of the text of the "Corpus Juris", has the force of canon law, even when it differs from that of St. Raymond. It is forbidden to introduce any change into that text (Papal Brief "Cum pro munere", 1 July, 1580). Among the other editions, mention may be made of that by Le Conte (Antwerp, 1570), of prior date to the Roman edition and containing the partes decis ; that of the brothers Pithou (Paris, 1687); that of Böhmer (Halle, 1747), which did not reproduce the text of the Roman edition and was in its textual criticism more audacious than happy; the edition of Richter (Leipzig, 1839) and that of Friedberg (Leipzig, 1879-1881). All these authors added critical notes and the partes decis.
To indicate the principal commentators on the Decretals would mean writing a history of canon law in the Middle Ages. Important canonist include Innocent IV (died 1254), Enrico de Segusio or Hostiensis (died 1271), the "Abbas antiquus" (thirteenth century), Johannes Andreæ, Baldus de Ubaldis (died 1400), Petrus de Ancharano (died 1416), Franciscus de Zabarellis (died 1417), Dominicus a Sancto Geminiano (fifteenth century), Joannes de Imola (died 1436) and Nicolò Tudesco also called the "Abbas Siculus", or "Modernus", or "Panormitanus" (died 1453). Among the modern commentators, Manuel Gonzalez Tellez and Fagnanus may be consulted advantageously for the interpretation of the text of the Decretals. The Decretals of Gregory IX remain the basis of canon law so far as it has not been modified by subsequent collections and by the general laws of the Church (see Corpus Juris Canonici).