John XXI, Pope

GIOVANNI XXI, POPE. — Born in Lisbon, probably between 1210 and 1220, elected on 8 September 1276, died on 20 May 1277. Pietro di Giuliano, a Portuguese, had studied in Paris and taught medicine at Siena between 1247 and 1252; he had then been among the household of Cardinal Ottobono de' Fieschi, the future Adrian V, and subsequently became dean of Lisbon (1261), archbishop of Braga (1273), archiatrist to Gregory X, who promoted him to cardinal bishop of Tusculum (1273).

After a tumultuous Conclave, he was elected at Viterbo as the successor of Adrian V and crowned on 20 September. As soon as he ascended to the pontificate, he punished the authors of the disturbances; but he confirmed a decree of Adrian suspending Gregory X’s constitution concerning the expedition of the papal election, intending to replace it with new regulations (30 September 1276). A man of study rather than of government, dominated by Cardinal Orsini, who later became Nicholas III, G. nevertheless displayed considerable activity during the few months of his pontificate. Following the path already taken by Gregory X, he sought to reconcile Rudolf of Habsburg and Charles of Anjou in order to make possible Rudolf’s coronation and peace in Italy; at the same time, however, he wished to prevent Charles’s excessive power and demanded from Rudolf a promise not to attack the dominion of the Church in Romagna. He sent two friars to reconcile Alfonso X of Castile and Philip III of France, threatening them with excommunication should they go to war.

He wished to unite all the Christian princes for the Crusade and collected tithes for the undertaking; he also considered an alliance with the Tatar rulers, who had sent him an embassy. He worked to make effective the union between the Greek and Roman Churches, decided upon at the Council of Lyons. He ordered Stefano Tempier, bishop of Paris, to investigate the new errors spreading in that University (18 January 1277); and, when the bishop had pronounced the condemnation of Averroism and the theory of the double truth (7 March 1277), he ordered him to proceed with the purification of the masters of both arts and theology (28 April 1277). The collapse of a floor in the Papal Palace at Viterbo brought to an end a pontificate that had promised to be beneficial to the Church and to the peace of the world.

More than for the achievements of his brief pontificate, «Pietro Ispano» became famous for his scientific and philosophical learning, on account of which Fra Salimbene calls him «magnus sophista, loycus et disputator atque theologus», while Dante places him in the second «garland» of theologians in the heaven of the Sun (Par., XII, 134-35). He composed books on medicine, following the Greco-Arabic tradition; among them were a De oculo and a Thesaurus pauperum, seu de medendis humani corporis membris, in which, with a sense of Christian compassion for those without financial means, he indicates how to treat every illness. He wrote a treatise De anima and commented on Aristotle’s De animalibus in the version of Michele Scoto. But, already according to Dante, he «shines» above all for the «twelve little books» of the Summulae logicales, a manual of dialectics, for which he drew upon the Summa of Lamberto di Auxerre and the work of Michele Psello. On the basis of Aristotelian-Boethian logic, he sets out all the forms of dialectical disputation and adds to them the contributions of what came to be called logica modernorum, dealing de proprietatibus

terminorum, that is, with the properties of logical terms and their relations to grammatical terms. The work enjoyed enormous circulation in manuscript from an early date; first printed at Alost in 1474, it had numerous subsequent editions (Prantl records no fewer than 84); it was also translated into Greek.