Voici un extrait d`une lettre du Cardinal Ratzinger concernant "Ordinatio Sacerdotalis" de Jean-Paul II(cet extrait est malheureusement en anglais car je ne l`ai pas trouvé en français sur internet):

"In response to this precise act of the Magisterium of the Roman Pontiff, explicitly addressed to the entire Catholic Church, all members of the faithful are required to give their assent to the teaching stated therein. To this end, the Congregation for the Doctrine of the Faith, with the approval of the Holy Father, has given an official Reply on the nature of this assent; it is a matter of full definitive assent, that is to say, irrevocable, to a doctrine taught infallibly by the Church. In fact, as the Reply explains, the definitive nature of this assent derives from the truth of the doctrine itself, since, founded on the written Word of God, and constantly held and applied in the Tradition of the Church, it has been set forth infallibly by the ordinary universal Magisterium (cf. Lumen Gentium, 25). Thus, the Reply specifies that this doctrine belongs to the deposit of the faith of the Church. It should be emphasized that the definitive and infallible nature of this teaching of the Church did not arise with the publication of the Letter Ordinatio Sacerdotalis. In the Letter, as the Reply of the Congregation for the Doctrine of the Faith also explains, the Roman Pontiff, having taken account of present circumstances, has confirmed the same teaching by a formal declaration, giving expression once again to quod semper, quod ubique et quod ab omnibus tenendum est, utpote ad fidei depositum pertinens. In this case, an act of the ordinary Papal Magisterium, in itself not infallible, witnesses to the infallibility of the teaching of a doctrine already possessed by the Church."

Le Cardinal affirme donc qu`un enseignement du magistère papal ordinaire n`est pas en soi infaillible mais seulement quand il est conforme aux Écritures et à la Tradition.

CQFD