"The Church has no philosophy of her own nor does she canonize any one particular philosophy in preference to others. (Cf. Pius XII, Encyclical Letter Humani generis (12 August 1950): AAS 42 (1950), 566.) The underlying reason for this reluctance is that, even when it engages theology, philosophy must remain faithful to its own principles and methods. Otherwise there would be no guarantee that it would remain oriented to truth and that it was moving towards truth by way of a process governed by reason. A philosophy which did not proceed in the light of reason according to its own principles and methods would serve little purpose. At the deepest level, the autonomy which philosophy enjoys is rooted in the fact that reason is by its nature oriented to truth and is equipped moreover with the means necessary to arrive at truth. A philosophy conscious of this as its “constitutive status” cannot but respect the demands and the data of revealed truth." (Pope John Paul II, Fides et ratio, § 54).
Thomas should be called not only the Angelic, but also the Common or Universal Doctor of the Church; for the Church has adopted his philosophy for her own, as innumerable documents of every kind attest. (Pope Pius XI, Studiorum Ducem, § 11).
"14. In theology some want to reduce to a minimum the meaning of dogmas; and to free dogma itself from terminology long established in the Church and from philosophical concepts held by Catholic teachers, to bring about a return in the explanation of Catholic doctrine to the way of speaking used in Holy Scripture and by the Fathers of the Church. They cherish the hope that when dogma is stripped of the elements which they hold to be extrinsic to divine revelation, it will compare advantageously with the dogmatic opinions of those who are separated from the unity of the Church and that in this way they will gradually arrive at a mutual assimilation of Catholic dogma with the tenets of the dissidents.
15. Moreover, they assert that when Catholic doctrine has been reduced to this condition, a way will be found to satisfy modern needs, that will permit of dogma being expressed also by the concepts of modern philosophy, whether of immanentism or idealism or existentialism or any other system. Some more audacious affirm that his can and must be done, because they hold that the mysteries of faith are never expressed by truly adequate concepts but only by approximate and ever changeable notions, in which the truth is to some extent expressed, but is necessarily distorted. Wherefore they do not consider it absurd, but altogether necessary, that theology should substitute new concepts in place of the old ones in keeping with the various philosophies which in the course of time it uses as its instruments, so that it should give human expression to divine truths in various ways which are even somewhat opposed, but still equivalent, as they say. They add that the history of dogmas consists in the reporting of the various forms in which revealed truth has been clothed, forms that have succeeded one another in accordance with the different teachings and opinions that have arisen over the course of the centuries.
16. It is evident from what We have already said, that such tentatives not only lead to what they call dogmatic relativism, but that they actually contain it. The contempt of doctrine commonly taught and of the terms in which it is expressed strongly favor it. Everyone is aware that the terminology employed in the schools and even that used by the Teaching Authority of the Church itself is capable of being perfected and polished; and we know also that the Church itself has not always used the same terms in the same way. It is also manifest that the Church cannot be bound to every system of philosophy that has existed for a short space of time. Nevertheless, the things that have been composed through common effort by Catholic teachers over the course of the centuries to bring about some understanding of dogma are certainly not based on any such weak foundation. These things are based on principles and notions deduced from a true knowledge of created things. In the process of deducing, this knowledge, like a star, gave enlightenment to the human mind through the Church. Hence it is not astonishing that some of these notions have not only been used by the Oecumenical Councils, but even sanctioned by them, so that it is wrong to depart from them....
30. Of course this philosophy deals with much that neither directly nor indirectly touches faith or morals, and which consequently the Church leaves to the free discussion of experts. But this does not hold for many other things, especially those principles and fundamental tenets to which We have just referred. However, even in these fundamental questions, we may clothe our philosophy in a more convenient and richer dress, make it more vigorous with a more effective terminology, divest it of certain scholastic aids found less useful, prudently enrich it with the fruits of progress of the human mind. But never may we overthrow it, or contaminate it with false principles, or regard it as a great, but obsolete, relic. For truth and its philosophic expression cannot change from day to day, least of all where there is question of self-evident principles of the human mind or of those propositions which are supported by the wisdom of the ages and by divine revelation. Whatever new truth the sincere human mind is able to find, certainly cannot be opposed to truth already acquired, since God, the highest Truth, has created and guides the human intellect, not that it may daily oppose new truths to rightly established ones, but rather that, having eliminated errors which may have crept in, it may build truth upon truth in the same order and structure that exist in reality, the source of truth. Let no Christian therefore, whether philosopher or theologian, embrace eagerly and lightly whatever novelty happens to be thought up from day to day, but rather let him weigh it with painstaking care and a balanced judgment, lest he lose or corrupt the truth he already has, with grave danger and damage to his faith.
31. If one considers all this well, he will easily see why the Church demands that future priests be instructed in philosophy "according to the method, doctrine, and principles of the Angelic Doctor," since, as we well know from the experience of centuries, the method of Aquinas is singularly preeminent both for teaching students and for bringing truth to light; his doctrine is in harmony with divine revelation, and is most effective both for safeguarding the foundation of the faith, and for reaping, safely and usefully, the fruits of sound progress.....
32. How deplorable it is then that this philosophy, received and honored by the Church, is scorned by some, who shamelessly call it outmoded in form and rationalistic, as they say, in its method of thought. They say that this philosophy upholds the erroneous notion that there can be a metaphysic that is absolutely true; whereas in fact, they say, reality, especially transcendent reality, cannot better be expressed than by disparate teachings, which mutually complete each other, although they are in a way mutually opposed. Our traditional philosophy, then, with its clear exposition and solution of questions, its accurate definition of terms, its clear-cut distinctions, can be, they concede, useful as a preparation for scholastic theology, a preparation quite in accord with medieval mentality; but this philosophy hardly offers a method of philosophizing suited to the needs of our modern culture. They allege, finally, that our perennial philosophy is only a philosophy of immutable essences, while the contemporary mind must look to the existence of things and to life, which is ever in flux. While scorning our philosophy, they extol other philosophies of all kinds, ancient and modern, oriental and occidental, by which they seem to imply that any kind of philosophy or theory, with a few additions and corrections if need be, can be reconciled with Catholic dogma. No Catholic can doubt how false this is, especially where there is question of those fictitious theories they call immanentism, or idealism, or materialism, whether historic or dialectic, or even existentialism, whether atheistic or simply the type that denies the validity of the reason in the field of metaphysics.