0 To the Patriarchs, Primates, Archbishops, and Bishops of the Catholic World in Grace and Communion with the Apostolic See. The only-begotten Son of the Eternal Father, who came on earth to bring salvation and the light of divine wisdom to men, conferred a great and wonderful blessing on the world when, about to ascend again into heaven, He commanded the Apostles to go and teach all nations,(1) and left the Church which He had founded to be the common and supreme teacher of the peoples. For men whom the truth had set free were to be preserved by the truth; nor would the fruits of heavenly doctrines by which salvation comes to men have long remained had not the Lord Christ appointed an unfailing teaching authority to train the minds to faith. And the Church built upon the promises of its own divine Author, whose charity it imitated, so faithfully followed out His commands that its constant aim and chief wish was this: to teach religion and contend forever against errors. To this end assuredly have tended the incessant labors of individual bishops; to this end also the published laws and decrees of councils, and especially the constant watchfulness of the Roman Pontiffs, to whom, as successors of the blessed Peter in the primacy of the Apostles, belongs the right and office of teaching and confirming their brethren in the faith. Since, then, according to the warning of the apostle, the minds of Christ's faithful are apt to be deceived and the integrity of the faith to be corrupted among men by philosophy and vain deceit,(2) the supreme pastors of the Church have always thought it their duty to advance, by every means in their power, science truly so called, and at the same time to provide with special care that all studies should accord with the Catholic faith, especially philosophy, on which a right interpretation of the other sciences in great part depends. Indeed, venerable brethren, on this very subject among others, We briefly admonished you in Our first encyclical letter; but now, both by reason of the gravity of the subject and the condition of the time, we are again compelled to speak to you on the mode of taking up the study of philosophy which shall respond most fitly to the excellence of faith, and at the same time be consonant with the dignity of human science.
Source: Aeterni Patris (Vatican.va)