Leo XIII, 1810–1903, pope (1878–1903), an Italian (b. Carpineto, E of Rome) named Gioacchino Pecci; successor of Pius IX. Ordained in 1837, he earned an excellent reputation as archbishop of Perugia (1846–77), and was created cardinal in 1853. Leo's election brought a turn in the course of the papacy; he was abreast of the times and tried, especially by preaching to the whole church, in encyclical letters, to form Roman Catholic attitudes appropriate to living in the modern world. His influence was increased by the length of his reign; thus he was able to furnish the college of cardinals with an unusual number of excellent men (including John Henry Newman in 1879 and James Gibbons in 1886). By a combination of vigor and tact he ended the Kulturkampf (1887). He tried repeatedly to bring French Roman Catholics to support the republic. In 1885 his encyclical Immortale Dei charted the course of Catholics as responsible citizens in modern secular, democratic states; he thus refuted both the French royalists' claim that they were especially good Catholics and the contention of French anti-Catholics that the church was committed to political reaction. The letter was a great vindication of Catholic democrats. With the anti-Catholic government of Italy there was no conciliation. Leo's program for society appeared in Rerum novarum (1891), an arraignment of capitalism that also showed the insufficiencies of Marxian socialism; it set up Catholic aims and ideals. (It was supplemented in Quadragesimo Anno  of Pius XI and in Mater et Magistra  of John XXIII.) Leo met the intellectual attack on Christianity by advancing Thomism, with its insistence that there can be no conflict between science and faith; to this end he wrote Aeterni Patris (1879), declaring the philosophy of St. Thomas Aquinas official and requiring its study; he also founded the institute of Thomistic philosophy at the Univ. of Louvain. He was profoundly interested in the advancement of learning. He opened the Vatican secret archives to all scholars, and he reminded Catholic historians that nothing but the whole truth must be found in their work. He encouraged Bible study and set up (1902) the permanent Biblical Commission. He sponsored a number of faculties and universities, including the Catholic Univ. at Washington, D.C. For sheer productivity Leo surpassed all his predecessors in modern times. He was succeeded by Pius X.
See biography by K. K. Burton (1962); studies by L. P. Wallace (1966) and J. Watzlawik (1966); E. Gilson, ed., The Church Speaks to the Modern World (tr. 1954; con aining nine encyclicals of Pope Leo XIII); E. T. Gargan, ed., Leo XIII and the Modern World (1961).
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