Born Compiègne, (Oise), France, 1350 or 1351
Died Avignon, France, 1420
Pierre d’Ailly remained an important authority for cosmographers and astrologers throughout the Renaissance period.
D’Ailly was born in Compiègne to prosperous burghers Colard d’Ailly and his wife Pétronille. D’Ailly studied at the University of Paris, where he received the licentiate in arts in 1367 and became a doctor of theology on 11 April 1381. D’Ailly had a distinguished career in both university and church, serving as rector of the College of Navarre of the University of Paris from 1384, chancellor of the University of Paris from 1389 to 1395, Bishop of Le Puy from 1395 to 1396, Bishop of Noyon from 1396 to 1397, Bishop of Cambrai from 1397, and Cardinal from 1411 until his death in Avignon in 1420. One of the most prominent churchmen during the years of the Great Schism (1378–1414), d’Ailly was also a prolific author in the areas of theology, ecclesiology, and natural philosophy, including astrology.
D’Ailly’s interest in the stars dates back to his days in Paris, although his early writings reveal no great expertise in or love of astrology. Two treatises with basic astronomical material, the Tractatus super libros metheororum de impressionibus aeris(a commentary on Aristotle ’s Meteorology, including sections on comets) and the Questioneson John of Holywood ’s Sphera(a commentary on a basic astronomical textbook), most likely date from his years of lecturing in the faculty of arts (1368–1374). D’Ailly’s early hostility to astrological predictions emerges in other treatises written in Paris before 1395, such as the De falsis prophetis, II(On false prophets, II) and the Tractatus utilis super Boecii de consolatione philosophie(a commentary on Boethius ’s Consolation of Philosophy). Despite these early condemnations, d’Ailly wholeheartedly embraced the “science of the stars” in the years after 1410.
In the final decade of his life, inspired by a reading of the Franciscan Roger Bacon , d’Ailly composed an important series of cosmological and astrological treatises, including Imago mundi(Image of the world, 1410), De legibus et sectis contra superstitiosos astronomos(On the laws and the sects, against the superstitious astrologers, 1410), Vigintiloquium de concordantia astronomie cum theologia(Twenty sayings on the concordance of astrology and theology, 1414), and Concordantia astronomie cum hystorica narratione(Concordance of astrology with the narration of history, 1414). In these treatises, d’Ailly defended astrology’s use in predicting large-scale change, including mutations in religions, and demonstrated particular expertise in the astrological doctrine of the great conjunctions. The latter teaching represented a means of making long-term predictions based largely on the pattern formed by successive mean conjunctions of Saturn and Jupiter. Those conjunctions falling every 240 years (great conjunctions) and 960 years (greatest conjunctions) were said to have particular significance for human affairs. D’Ailly also explored the vexing problem of calendrical reform in treatises such as Exhortatio super Kalendarii correctione(Exhortation to the correction of the calendar, 1411; presented to Pope John XXIII and also read before the Council of Constance) and De vero cyclo lunari(probably from the same time). The culmination of d’Ailly’s astrological studies, revealed in the Concordantia astronomie cum hystorica narrationeand again in the treatise De persecutionibus ecclesie(On the persecutions of the church), completed in 1418, was his prediction of the appearance of the Antichrist in or around the year 1789. Only a century earlier, scholars had denied that such an astrological prediction of the apocalypse was possible or licit. D’Ailly’s prognostication for 1789 rested on the convergence of three astrological signifiers: a greatest conjunction of Saturn and Jupiter, the completion of ten revolutions by the planet Saturn, and an alteration in the position attained by the accessusand recessusof the eighth sphere. (The latter phrase refers to one of the explanations of the precession of the equinoxes offered in the Alfonsine Tables). First proposed on the eve of the Council of Constance that would finally end decades of schism, d’Ailly’s prediction for 1789 offered reassuring hope that the division in the church did not, in fact, signal the imminent end of the world, as many had feared.
A number of d’Ailly’s astrological treatises appear in two important incunable editions (Louvain 1483 and Augsburg 1490) as well as in numerous manuscript copies. His commentary on Sacrobosco’s Spherealso was printed a number of times in the fifteenth and sixteenth centuries. The noted astrologer Johann Müller (Regiomontanus) knew and praised his work on conjunctions. Christopher Columbus owned and annotated d’Ailly’s Imago mundiand other astrological works, and d’Ailly’s astrological predictions helped confirm Columbus’s own sense of apocalyptic mission. D’Ailly’s prognostication for 1789, and in particular his use of the period of accessusand recessusof the eighth sphere, formed a model for such later astrologers as Jean de Bruges in the 1440s and Pierre Turrell in the 1530s. Similarly, Müller praised his work on conjunctions. Through his prestige as scholar and cardinal and through his example of an astrological forecast of the end of the world, d’Ailly may be said to stand at the head of the flood of such astrological apocalyptic prognostications that engulfed Europe in the late fifteenth through seventeenth centuries.
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