The Relevance of Philosophy and the Heritage of Aquinas for the Work of Theologians
Encyclical Aeterni Patris
12. [...] But the writings on the human soul, the divine attributes, and other questions of mighty moment which the great Athanasius and Chrysostom, the prince of orators, have left behind them are, by common consent, so supremely excellent that it seems scarcely anything could be added to their subtlety and fulness. And, not to cover too wide a range, we add to the number of the great men of whom mention has been made the names of Basil the Great and of the two Gregories, who, on going forth from Athens, that home of all learning, thoroughly equipped with all the harness of philosophy, turned the wealth of knowledge which each had gathered up in a course of zealous study to the work of refuting heretics and preparing Christians.
13. But Augustine would seem to have wrested the palm from all. Of a most powerful genius and thoroughly saturated with sacred and profane learning, with the loftiest faith and with equal knowledge, he combated most vigorously all the errors of his age. What topic of philosophy did he not investigate? What region of it did he not diligently explore, either in expounding the loftiest mysteries of the faith to the faithful, or defending them against the full onslaught of adversaries, or again when, in demolishing the fables of the Academicians or the Manichaeans, he laid the safe foundations and sure structure of human science, or followed up the reason, origin, and causes of the evils that afflict man? How subtly he reasoned on the angels, the soul, the human mind, the will and free choice, on religion and the life of the blessed, on time and eternity, and even on the very nature of changeable bodies. Afterwards, in the East, John Damascene, treading in the footsteps of Basil and of Gregory of Nazianzen, and in the West, Boethius and Anselm following the doctrines of Augustine, added largely to the patrimony of philosophy.
14. Later on, the doctors of the middle ages, who are called Scholastics, addressed themselves to a great work-that of diligently collecting, and sifting, and storing up, as it were, in one place, for the use and convenience of posterity the rich and fertile harvests of Christian learning scattered abroad in the voluminous works of the holy Fathers. And with regard, venerable brethren, to the origin, drift, and excellence of this scholastic learning, it may be well here to speak more fully in the words of one of the wisest of Our predecessors, Sixtus V: "By the divine favor of Him who alone gives the spirit of science wisdom, and understanding, and who thou ages, as there may be need, enriches His Church with new blessings and strengthens it with safeguards, there was founded by Our fathers, men of eminent wisdom, the scholastic theology, which two glorious doctors in particular angelic St. Thomas and the seraphic St. Bonaventure, illustrious teachers of this faculty, with surpassing genius, by unwearied diligence, and at the cost of long labors and vigils, set in order and beautified, and when skilfuly arranged and clearly explained in a variety of ways, handed down to posterity.
15. "And, indeed, the knowledge and use of so salutary a science, which flows from the fertilizing founts of the sacred writings, the sovereign Pontiffs, the holy Fathers and the councils, must always be of the greatest assistance to the Church, whether with the view of really and soundly understanding and interpreting the Scriptures, or more safely and to better purpose reading and explaining the Fathers, or for exposing and refuting the various errors and heresies; and in these late days, when those dangerous times described by the Apostle are already upon us, when the blasphemers, the proud, and the seducers go from bad to worse, erring themselves and causing others to err, there is surely a very great need of confirming the dogmas of Catholic faith and confuting heresies."
16. Although these words seem to bear reference solely to Scholastic theology, nevertheless they may plainly be accepted as equally true of philosophy and its praises. For, the noble endowments which make the Scholastic theology so formidable to the enemies of truth-to wit, as the same Pontiff adds, "that ready and close coherence of cause and effect, that order and array as of a disciplined army in battle, those clear definitions and distinctions, that strength of argument and those keen discussions, by which light is distinguished from darkness, the true from the false, expose and strip naked, as it were, the falsehoods of heretics wrapped around by a cloud of subterfuges and fallacies" - those noble and admirable endowments, We say, are only to be found in a right use of that philosophy which the Scholastic teachers have been accustomed carefully and prudently to make use of even in theological disputations. Moreover, since it is the proper and special office of the Scholastic theologians to bind together by the fastest chain human and divine science, surely the theology in which they excelled would not have gained such honor and commendation among men if they had made use of a lame and imperfect or vain philosophy.
17. Among the Scholastic Doctors, the chief and master of all towers Thomas Aquinas, who, as Cajetan observes, because "he most venerated the ancient doctors of the Church, in a certain way seems to have inherited the intellect of all." The doctrines of those illustrious men, like the scattered members of a body, Thomas collected together and cemented, distributed in wonderful order, and so increased with important additions that he is rightly and deservedly esteemed the special bulwark and glory of the Catholic faith. With his spirit at once humble and swift, his memory ready and tenacious, his life spotless throughout, a lover of truth for its own sake, richly endowed with human and divine science, like the sun he heated the world with the warmth of his virtues and filled it with the splendor of his teaching. 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.
18. Moreover, the Angelic Doctor pushed his philosophic inquiry into the reasons and principles of things, which because they are most comprehensive and contain in their bosom, so to say, the seeds of almost infinite truths, were to be unfolded in good time by later masters and with a goodly yield. And as he also used this philosophic method in the refutation of error, he won this title to distinction for himself: that, single-handed, he victoriously combated the errors of former times, and supplied invincible arms to put those to rout which might in after-times spring up. Again, clearly distinguishing, as is fitting, reason from faith, while happily associating the one with the other, he both preserved the rights and had regard for the dignity of each; so much so, indeed, that reason, borne on the wings of Thomas to its human height, can scarcely rise higher, while faith could scarcely expect more or stronger aids from reason than those which she has already obtained through Thomas.
19. For these reasons most learned men, in former ages especially, of the highest repute in theology and philosophy, after mastering with infinite pains the immortal works of Thomas, gave themselves up not so much to be instructed in his angelic wisdom as to be nourished upon it. It is known that nearly all the founders and lawgivers of the religious orders commanded their members to study and religiously adhere to the teachings of St. Thomas, fearful least any of them should swerve even in the slightest degree from the footsteps of so great a man. To say nothing of the family of St. Dominic, which rightly claims this great teacher for its own glory, the statutes of the Benedictines, the Carmelites, the Augustinians, the Society of Jesus, and many others all testify that they are bound by this law.
20. And, here, how pleasantly one's thoughts fly back to those celebrated schools and universities which flourished of old in Europe - to Paris, Salamanca, Alcalá, to Douay, Toulouse, and Louvain, to Padua and Bologna, to Naples and Coimbra, and to many another! All know how the fame of these seats of learning grew with their years, and that their judgment, often asked in matters of grave moment, held great weight everywhere. And we know how in those great homes of human wisdom, as in his own kingdom, Thomas reigned supreme; and that the minds of all, of teachers as well as of taught, rested in wonderful harmony under the shield and authority of the Angelic Doctor.
21. But, furthermore, Our predecessors in the Roman pontificate have celebrated the wisdom of Thomas Aquinas by exceptional tributes of praise and the most ample testimonials. Clement VI in the bull In Ordine; Nicholas V in his brief to the friars of the Order of Preachers, 1451; Benedict XIII in the bull Pretiosus, and others bear witness that the universal Church borrows lustre from his admirable teaching; while St. Pius V declares in the bull Mirabilis that heresies, confounded and convicted by the same teaching, were dissipated, and the whole world daily freed from fatal errors; others, such as Clement XII in the bull Verbo Dei, affirm that most fruitful blessings have spread abroad from his writings over the whole Church, and that he is worthy of the honor which is bestowed on the greatest Doctors of the Church, on Gregory and Ambrose, Augustine and Jerome; while others have not hesitated to propose St. Thomas for the exemplar and master of the universities and great centers of learning whom they may follow with unfaltering feet. On which point the words of Blessed Urban V to the University of Toulouse are worthy of recall: "It is our will, which We hereby enjoin upon you, that ye follow the teaching of Blessed Thomas as the true and Catholic doctrine and that ye labor with all your force to profit by the same." Innocent XII, followed the example of Urban in the case of the University of Louvain, in the letter in the form of a brief addressed to that university on February 6, 1694, and Benedict XIV in the letter in the form of a brief addressed on August 26, 1752, to the Dionysian College in Granada; while to these judgments of great Pontiffs on Thomas Aquinas comes the crowning testimony of Innocent VI: "His teaching above that of others, the canonical writings alone excepted, enjoys such a precision of language, an order of matters, a truth of conclusions, that those who hold to it are never found swerving from the path of truth, and he who dare assail it will always be suspected of error."
22. The ecumenical councils, also, where blossoms the flower of all earthly wisdom, have always been careful to hold Thomas Aquinas in singular honor. In the Councils of Lyons, Vienna, Florence, and the Vatican one might almost say that Thomas took part and presided over the deliberations and decrees of the Fathers, contending against the errors of the Greeks, of heretics and rationalists, with invincible force and with the happiest results. But the chief and special glory of Thomas, one which he has shared with none of the Catholic Doctors, is that the Fathers of Trent made it part of the order of conclave to lay upon the altar, together with sacred Scripture and the decrees of the supreme Pontiffs, the Summa of Thomas Aquinas, whence to seek counsel, reason, and inspiration.
23. A last triumph was reserved for this incomparable man-namely, to compel the homage, praise, and admiration of even the very enemies of the Catholic name. For it has come to light that there were not lacking among the leaders of heretical sects some who openly declared that, if the teaching of Thomas Aquinas were only taken away, they could easily battle with all Catholic teachers, gain the victory, and abolish the Church. A vain hope, indeed, but no vain testimony.
24. Therefore, venerable brethren, as often as We contemplate the good, the force, and the singular advantages to be derived from his philosophic discipline which Our Fathers so dearly loved. We think it hazardous that its special honor should not always and everywhere remain, especially when it is established that daily experience, and the judgment of the greatest men, and, to crown all, the voice of the Church, have favored the Scholastic philosophy. Moreover, to the old teaching a novel system of philosophy has succeeded here and there, in which We fail to perceive those desirable and wholesome fruits which the Church and civil society itself would prefer.
 Sixtus V, Bulla Triumphantis (1588).
 Thomas de Vio Cajetan's, Commentary on Summa Theologiae, IIa-IIae, q. 148, 9. a. 4.
 Urban V, Constitutio 5a, given to the University of Toulouse, August 3, 1368.
 Innocent VI, Sermo de S. Thoma.