Whenever the pope teaches about the other sacred thing we keep in our pants–our wallets–one often hears “The Pope was not speaking ex cathedra…. We can thus choose to accept it or not.”  We also often hear that his teaching is some kind of radical departure from the traditional teaching of the Church.  You know:  one of those liberal Vatican II things.
From Lumen Gentium, the Dogmatic Constitution on the Church, chapter 3:
“Among the principal duties of bishops the preaching of the Gospel occupies an eminent place. For bishops are preachers of the faith, who lead new disciples to Christ, and they are authentic teachers, that is, teachers endowed with the authority of Christ, who preach to the people committed to them the faith they must believe and put into practice, and by the light of the Holy Spirit illustrate that faith. They bring forth from the treasury of Revelation new things and old, making it bear fruit and vigilantly warding off any errors that threaten their flock. Bishops, teaching in communion with the Roman Pontiff, are to be respected by all as witnesses to divine and Catholic truth. In matters of faith and morals, the bishops speak in the name of Christ and the faithful are to accept their teaching and adhere to it with a religious assent. This religious submission of mind and will must be shown in a special way to the authentic magisterium of the Roman Pontiff, even when he is not speaking ex cathedra; that is, it must be shown in such a way that his supreme magisterium is acknowledged with reverence, the judgments made by him are sincerely adhered to, according to his manifest mind and will. His mind and will in the matter may be known either from the character of the documents, from

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