Aeterni Patris (Pope Leo XIII)

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Aeterni Patris  (1893) 
by Pope Leo XIII
Given at Rome, at St. Peter's, on the 4th day of August, 1879. This edition is taken from The Summa Theologica of St. Thomas Aquinas, published 1912 by Burns Oates & Washbourne.











To His Venerable Brethren, all the Patriarchs, Primates, Archbishops, and Bishops of the Catholic World, in favour and communion with the Apostolic See,


Venerable Brethren,

Health and Apostolic Benediction.

The Only-begotten Son of the Eternal Father appeared on earth to bring salvation and the light of the wisdom of God to the human race. As He was ascending to Heaven He bestowed on the world a blessing, truly great and wondrous, when, commanding His Apostles to 'go and teach all nations,'[1] He left a Church, founded by Himself, as the universal and supreme mistress of all people. Man, whom the truth had set free, was to be kept safe by the truth. Indeed, the fruits of heavenly doctrine, by which salvation was gained for man, could not have endured for long unless Christ our Lord had set up a perpetual teaching authority (magisterium) for the instruction of souls in the faith. This Church, then, not only built on the promises of its Divine Author, but following in His love, has kept His commands. She has always looked to one end, and desired it with great desire; that is, to teach the true religion and wage ceaseless war with error. For this there have been the watchful labours of Bishops, each in his own place; and for this Councils have made laws and decrees. More than all, for this there has been the daily anxiety of the Roman Pontiffs. They are the successors of Blessed Peter, the Prince of the Apostles, in his Primacy, and therefore it is their right and their duty to teach the brethren, and confirm them in the faith.

Now, the Apostle warns us that the faithful of Christ are often deceived in mind 'by philosophy and vain deceit,'[2] and that thus the sincerity of faith is corrupted in men. For this reason the Supreme Pastors of the Church have always held that it is part of their office to advance, with all their power, knowledge truly so called; but at the same time to watch with the greatest care that all human learning shall be imparted according to the rule of the Catholic faith. Especially is this true of 'philosophy,' on which the right treatment of other sciences depends in great measure. We Ourselves spoke to you shortly of this, among other things, Venerable Brothers, when first We addressed you all by an Encyclical Letter. Now, by the importance of this matter, and by the state of the times, We are forced again to write to you, that you may so organize the course of philosophical studies as to insure their perfect correspondence with the gift of Faith, and also their agreement with the dignity of human knowledge.

If anyone look carefully at the bitterness of our times, and if, further, he consider earnestly the cause of those things that are done in public and in private, he will discover with certainty the fruitful root of the evils which are now overwhelming us, and of the evils which we greatly fear. The cause he will find to consist in this—evil teaching about things, human and divine, has come forth from the schools of philosophers; it has crept into all the orders of the State; and it has been received with the common applause of very many. Now, it has been implanted in man by Nature to follow reason as the guide of his actions, and therefore, if the understanding go wrong in anything, the will easily follows. Hence it comes about that wicked opinions in the understanding, flow into human actions and make them bad. On the other hand, if the mind of man be healthy, and strongly grounded in solid and true principles, it will assuredly be the source of great blessings, both as regards the good of individuals and as regards the common weal.

We do not, indeed, attribute to human philosophy such force and authority as to judge it sufficient for the utter shutting out and uprooting of all errors. When the Christian religion was first established by the wondrous light of Faith shed abroad, 'not in the persuasive words of human wisdom,[3] but in showing of the Spirit and power,' the whole world was restored to its primeval dignity. So also now, chiefly from the almighty power and help of God, we may hope that the darkness of error will be taken away from the minds of men, and that they will repent. But we must not despise or undervalue those natural helps which are given to man by the kindness and wisdom of God, Who strongly and sweetly orders all things; and it stands to reason that a right use of philosophy is the greatest of these helps. For God did not give the light of reason in vain to the soul of man, nor does the superadded light of Faith quench, or even lessen, the strength of the understanding. Its effect is far from this. It perfects the understanding, gives it new strength, and makes it fit for greater works. The very nature of the providence of God Himself, therefore, makes it needful for us to seek a safeguard in human knowledge when we strive to bring back the people to Faith and salvation. The records of antiquity bear witness that this method, both probable and wise, was used habitually by the most illustrious Fathers of the Church. They, in truth, were wont to give to reason offices neither few nor small; and these the great Augustine has summed up very shortly: 'Attributing to this science … that by which the life-giving Faith … is begotten, nourished, guarded, and strengthened.'

In the first place, then, if philosophy be rightly and wisely used, it is able in a certain measure to pave and to guard the road to the true Faith; and is able, also, to prepare the minds of its followers in a fitting way for the receiving of revelation. Hence it has not untruly been called by the ancients 'an education leading to the Christian Faith,' 'a prelude and help of Christianity,' 'a schoolmaster for the Gospel.'

In truth, the loving-kindness of God, with regard to the things concerning Himself, has not only made known by the light of Faith many truths beyond the reach of the human understanding, but has also revealed some which are not altogether beyond the power of reason to find out. Such truths, when the authority of God is thus added, become known to all both at once and without any mixture of error. This being so, certain truths, either divinely revealed to us for our belief, or bound up closely with the doctrine of the Faith, were known to wise men among the Gentiles, who were guided only by the light of natural reason. By fitting arguments they vindicated and demonstrated these truths. St. Paul says: 'The invisible things of Him, from the creation of the world, are clearly seen, being understood by the things that are made; His eternal power also and divinity.' Again: 'The Gentiles, who have not the law,' nevertheless 'show the work of the law written in their hearts.'

It is opportune, therefore, in a high degree to use, for the good and the advantage of revealed truth, these other truths that were known even to wise heathens; for thus human wisdom, and the very testimony of the adversaries, give their witness to the Catholic Faith. Further, it is plain that this way of treating the question is not a thing newly devised, but an ancient way very much used by the holy Fathers of the Church. Moreover, these venerable witnesses and guardians of holy traditions see a kind of form of this, and almost a type of it, in one action of the Hebrews; who, as they were going out of Egypt, were commanded to take with them vessels of silver and of gold, with precious garments of the Egyptians. This was done that, by a use suddenly changed, the riches which had ministered to superstition and to rites of ignominy might be dedicated to the service of the true God. Gregory of Neocæsaræa praises Origen for this very reason, that, skilfully gathering together Page:Summa Theologica (2nd rev. ed.) - Volume 1.djvu/19 Page:Summa Theologica (2nd rev. ed.) - Volume 1.djvu/20 Page:Summa Theologica (2nd rev. ed.) - Volume 1.djvu/21 Page:Summa Theologica (2nd rev. ed.) - Volume 1.djvu/22 Page:Summa Theologica (2nd rev. ed.) - Volume 1.djvu/23 Page:Summa Theologica (2nd rev. ed.) - Volume 1.djvu/24 Page:Summa Theologica (2nd rev. ed.) - Volume 1.djvu/25 Page:Summa Theologica (2nd rev. ed.) - Volume 1.djvu/26 Page:Summa Theologica (2nd rev. ed.) - Volume 1.djvu/27 Page:Summa Theologica (2nd rev. ed.) - Volume 1.djvu/28 Page:Summa Theologica (2nd rev. ed.) - Volume 1.djvu/29 Page:Summa Theologica (2nd rev. ed.) - Volume 1.djvu/30 Page:Summa Theologica (2nd rev. ed.) - Volume 1.djvu/31 Page:Summa Theologica (2nd rev. ed.) - Volume 1.djvu/32 Page:Summa Theologica (2nd rev. ed.) - Volume 1.djvu/33 Page:Summa Theologica (2nd rev. ed.) - Volume 1.djvu/34 Page:Summa Theologica (2nd rev. ed.) - Volume 1.djvu/35 Page:Summa Theologica (2nd rev. ed.) - Volume 1.djvu/36 Page:Summa Theologica (2nd rev. ed.) - Volume 1.djvu/37 Page:Summa Theologica (2nd rev. ed.) - Volume 1.djvu/38 each, we give, with great love in the Lord, our Apostolical blessing, the earnest of heavenly gifts, and the witness of our special goodwill.

Given at Rome, at St. Peter's, this 4th day of August, 1879, in the second year of our Pontificate.


  1. Matt, xxviii. 19.
  2. Col. ii. 8.
  3. I Cor. ii. 4.