The Corpus Juris Canonici, or Corpus of…

The Corpus Juris Canonici, or Corpus of Canon Law, a set of six compilations of law in the Roman Catholic Church that provides the chief source of ecclesiastical legislation from the Middle Ages, includes four official collections: the Decretum Gratiani (“Decree of Gratian”), written between 1141 and 1150; the Decretals of Pope Gregory IX (1234); the Liber Sextus (“Book Six”) of Pope Boniface VIII (1298); and the Clementinae of Pope Clement V (1317); and two private collections: the Extravagantes of Pope John XXII (1325) and the Extravagantes communes (“Decretals Commonly Circulating”)—the decretals, or replies of the pope to particular questions of church discipline, from Pope Boniface VIII to Pope Sixtus IV—both of which had been compiled at the beginning of the sixteenth century by Jean Chappuis, a canonist at the University of Paris.

The title Corpus Juris Canonici had first been applied to the six collections by Pope Gregory XIII in the document Cum pro munere (1580), which approved an edition of the works as textually authentic.

These collections do not form a closed body of ecclesiastical law, prohibiting any new laws from being added, but, in fact, no new official collections of church law had been promulgated between the Clementinae and the Council of Trent (1545–63).

The bishops at the Council of Trent had requested new critical editions of Sacred Scripture, of liturgical books, and of the Corpus Juris Canonici.

In response to this request, a commission of cardinals and canonists have prepared a scientific critical edition of the Corpus between 1560 and 1582.

In 1582, Gregory XIII issues the revised text of the Corpus and ordered its use in schools of canon law and in church courts.

The Alexandrian astronomer Sosigenes, in creating the Julian calendar as a reform of the Roman republican calendar, had overestimated the length of the year by eleven minutes fourteen seconds, and by the mid-1500s, the cumulative effect of this error had shifted the dates of the seasons by about 10 days from Caesar's time.

Pope Gregory's reform, proclaimed in 1582, restores the calendar to the seasonal dates of CE 325, an adjustment of ten days.

Gregory bases his reform on restoration of the vernal equinox, now falling on March 11, to the date (March 21) it had in CE 325, the time of the Council of Nicaea, and not on the date of the equinox at the time of the birth of Christ, when it fell on March 25.

The change is effected by advancing the calendar ten days after October 4, 1582, the day following being reckoned as October 15.

The Gregorian calendar does not, however, include a year 0 in the transition from BC (years before Christ) to AD (those since his birth): the Gregorian calendar differs from the Julian only in that no century year is a leap year unless it is exactly divisible by 400 (e.g., 1600, 2000).

From this time forward, the Julian calendar will gradually be abandoned in favor of the Gregorian.