In Humanae vitae, his 1968 encyclical on the regulation of birth, St. Paul VI wrote that “any action which either before, at the moment of, or after sexual intercourse, is specifically intended to prevent procreation — whether as an end or as a means” is “excluded,” as an unlawful means of birth control.
Father Thomas Petri, O.P., president of the Dominican House of Studies in Washington, D.C. and a moral theologian, told CNA this month that “even if it's the case that any particular encyclical” such as Humanae vitae “is not infallible, the teaching that it presents is in fact irreformable, because it's part of the ordinary and universal magisterium of the Church.”
“In Veritatis splendor John Paul II does say that contraception is an intrinsically evil act, so there can be no reason or purpose for contraception. Benedict XVI gave several speeches in which he spoke about contraception, and it can't be changed. What was true yesterday is true today,” Petri noted.
“There can't be any sort of rollback of the teaching, because it's what’s always been taught, and that's how Catholic theology, and Catholic doctrine, works.”
Petri added that “It's not helpful to simply focus on infallibility and what is named infallible in an extraordinary way. The First Vatican Council, when it spoke about papal infallibility, was very clear that it was supposed to be an extraordinary act.”
Petri compared an infallible statement to an ecumenical council. He described it as “a very extraordinary act, and which usually only happens when the matter at issue, whether it's a doctrinal matter or a moral matter, has become so entirely embroiled in conflict … that it requires such an extraordinary act as a pope or a council declaring something infallibly.”
“That's not normally how Church teaching works — that's why the ordinary magisterium is important.”