Humani Generis §29

²⁹ It is well known how highly the Church regards human reason, for it falls to reason to demonstrate with certainty the existence of God, personal and one; to prove beyond doubt from divine signs the very foundations of the Christian faith; to express properly the law which the Creator has imprinted in the hearts of men; and finally to attain to some notion, indeed a very fruitful notion, of mysteries. But reason can perform these functions safely and well only when properly trained, that is, when imbued with that sound philosophy which has long been, as it were, a patrimony handed down by earlier Christian ages, and which moreover possesses an authority of an even higher order, since the Teaching Authority of the Church, in the light of divine revelation itself, has weighed its fundamental tenets, which have been elaborated and defined little by little by men of great genius. For this philosophy, acknowledged and accepted by the Church, safeguards the genuine validity of human knowledge, the unshakable metaphysical principles of sufficient reason, causality, and finality, and finally the mind's ability to attain certain and unchangeable truth.