AETERNI PATRIS (UNIGENITUS) — an encyclical letter proclaimed by Pope Leo XIII, July 4, 1879 (Acta Leonis Papae R, 1882, I 225-284). The subtitle of the encyclical, On the Restoration of Christian Philosophy in Catholic Schools in the Spirit (ad mentem) of the Angelic Doctor, St. Thomas Aquinas, indicated the need for a renewal of Christian philosophy and the direction the renewal should take.
The encyclical was divided into three parts and 34 paragraphs.
In the first part, it notes the benefits that true philosophy brings. True philosophy forms the reason and thereby the reason more easily accepts Revelation as the source for answers to the questions of the reason. It also proves many truths that overlap the domain of religion (Clement of Alexandria called it a stepping stone to the Christian Faith and a Gospel teacher, while St. Augustine attributes to philosophy that by which the faith is begotten, nourished, defended and made strong). It was due to philosophy in large measure that theology acquired the character of a systematic science.
The second part of the encyclical indicates the need to be aware of the limits of philosophical knowledge. This is particularly important with regard to the object of faith (revealed truths), which always remains a mystery to the human reason. The submission of the reason to Revelation benefits philosophy, since it allows philosophy to avoid many errors to which even the minds of geniuses succumbed when they acted only by their own powers. The encyclical mentions the names of those who "to the study of philosophy unite obedience to the Christian faith". They include St. Justin Martyr, Quadratus, Clement of Alexandria, Origen, Tertullian, Arnobius, Lactantius, Athanasius, Chrysostom, Basil, John Damascene, Boethius and Anselm. The names are drawn over the ages from the beginning of Christianity to late scholasticism. Among all the scholastics, St. Thomas Aquinas receives the highest praise. Several pages of the encyclical present his triumphal procession through the history of Christian culture. The oldest and most respected schools and universities of Europe followed the thought of Aquinas: Paris, Salamanca, Alcala, Toulouse, Louvain, Padua, Bologna, Naples, Coimbra and many others. Pope Leo XIII recalls his predecessors who gave exceptional praise to Aquinas: Clement VI, Innocent VI, Urban V, Nicholas V, Pius V, Clement XII, Innocent XII, Benedict XIII, and Benedict XIV. He mentions religions orders that took the philosophy of Aquinas as their own: the Dominicans, Benedictines, Carmelites, Jesuits and many others. Many ecumenical councils held the doctrine of St. Thomas in special honor (the Councils of Lyons, Florence, Trent, Vienna and the Vatican), and his doctrine was often cited in their decrees.
In the third and final part of the encyclical, Leo XIII expresses his sorrow that scholastic philosophy, which has borne so many precious fruits, lost importance in modern times and has passed into oblivion and has even been despised. This was detrimental not only for philosophy itself, but also for religion, science and the social order. All the more Leo XIII gives recognition to all who have not submitted to the general tendency but dedicated themselves to the rebirth of scholasticism. He also calls upon bishops and all Catholic philosophers to follow in the footsteps of the pioneers of the renewed scholastic philosophy. He gives directions as to how this rebirth should proceed if it is to be a progress rather than a regress. In addition to encouraging the study of traditional philosophy, he also exhorts scholars to be familiar with the findings of the sciences, since in view of the rapid progress of the sciences, "nothing was of greater use to the philosopher than diligently to search into the mysteries of nature and to be earnest and constant in the study of physical things" (Aeterni Patris, par. 30). For this reason, the truest and most fitting way for philosophy, which everyone should hold, is to connect the ancient wisdom harmoniously with progress and with the newest certain and well-proven discoveries.
The pope was convinced, as he often said in other pronouncements, that "without an acquaintance with of the findings of the most recent sciences, learning cannot be complete. In such quick progress of the mind, in this universal desire for science and the noble and praiseworthy pursuit of science, Catholics should lead the way and not lag behind others. Thus they have an obligation to acquire education in all areas and to exercise their minds to reach the truth" (I. Radziszewski, Encyklika o studyach filozoficznych [Encyclical on philosophical studies], Wwa 1902, 216).
The encyclical had two results: it confirmed the efforts of Catholic philosophers to renew scholastic philosophy and thereby contributed to rebuilding the bridge that had been destroyed between reason and faith, and it gave an impulse to the founding of many new philosophical centers: in 1902 there were active centers of neoscholastic studies in 14 countries (Belgium, France, Switzerland, Spain, Portugal, Italy, Germany, England, Ireland, the United States of America, Austria, Czechoslovakia, Hungary and Poland). In this period around 206 new periodicals dedicated to the questions of the renewed neoscholastic philosophy appeared, and each year about a thousand works were published.
The reason for practicing the renewed Christian philosophy "in the spirit (ad mentem) of St. Thomas Aquinas", the pope wrote, is that philosophy "has no part which he did not touch finely at once and thoroughly; on the laws of reasoning, on God and incorporeal substances, on man and other sensible things, on human actions and their principles, he reasoned in such a manner that in him there is wanting neither a full array of questions, nor an apt disposal of the various parts, nor the best method of proceeding, nor soundness of principles or strength of argument, nor clearness and elegance of style, nor a facility for explaining what is abstruse" (Aeterni Patris, par. 24).
I. Radziszewski, Encyklika o studyach filozoficznych (z 4 VIII 1879 r) "Aeterni Patris" [Encyclical on philosophical studies (Aug. 4, 1879) "Aeterni Patris], in: Leo XIII. Zywot i prace [Leo XIII, Life and works], Wwa 1902, 165-222; F. Ehrle, Zur Enzyklika "Aeterni Patris", R 1954; J.P. Gélinas, La restauration du thomisme sous Léon XIII et les philosophies nouvelles, Wa 1959; É. Gilson, Le philosophie et la théologie, P 1960 (Filozofia i teologia, Wwa 1968); M. Gogacz, Filozofia chrześcijańska w Polsce odrodzonej (1918-1968), SPCh 5 (1969), 2, 49-79.