Wherefore, let the faithful also be on their guard against the overrated independence of private judgment and that false autonomy of human reason. For it is quite foreign to everyone bearing the name of a Christian to trust his own mental powers with such pride as to agree only with those things which he can examine from their inner nature, and to imagine that the Church, sent by God to teach and guide all nations, is not conversant with present affairs and circumstances; or even that they must obey only in those matters which she has decreed by solemn definition as though her other decisions might be presumed to be false or putting forward insufficient motive for truth and honesty. (Papal Encyclical, Casti Connubii, 31 December 1930).
Men more advanced in age encounter a yet graver peril from evil teaching, which is of such a kind as to blind the young by misleading words, instead of filling them with the knowledge of the truth. Many now-a-days seek to learn by the aid of reason alone, laying divine faith entirely aside; and, through the removal of its bright light, they stumble and fail to discern the truth, teaching for instance, that matter alone exists in the world; that men and beasts have the same origin and a like nature; there are some, indeed, who go so far as to doubt the existence of God, the Ruler and Maker of the World, or who err most grievously, like the heathens, as to the nature of God. Hence the very nature and form of virtue, justice, and duty are of necessity destroyed. Thus it is that while they hold up to admiration the high authority of reason, and unduly elevate the subtlety of the human intellect, they fall into the just punishment of pride through ignorance of what is of more importance. (Papal Writings, Exeunte Iam Anno, 25 December 1888).