The truths that have to do with God and the relations between God and men, completely surpass the sensible order and demand self-surrender and self-abnegation in order to be put into practice and to influence practical life. Now the human intellect, in gaining the knowledge of such truths is hampered both by the activity of the senses and the imagination, and by evil passions arising from original sin. Hence men easily persuade themselves in such matters that what they do not wish to believe is false or at least doubtful. These new opinions, whether they originate from a reprehensible desire of novelty or from a laudable motive, are not always advanced in the same degree, with equal clarity nor in the same terms, nor always with unanimous agreement of their authors. Theories that today are put forward rather covertly by some, not without cautions and distinctions, tomorrow are openly and without moderation proclaimed by others more audacious, causing scandal to many, especially among the young clergy and to the detriment of ecclesiastical authority. Though they are usually more cautious in their published works, they express themselves more openly in their writings intended for private circulation and in conferences and lectures. Moreover, these opinions are disseminated not only among members of the clergy and in seminaries and religious institutions, but also among the laity, and especially among those who are engaged in teaching youth. (Papal Encyclical, Humani Generis, 12 August 1950).