Dear Ryan:

In order for a teaching to be infallible by the extraordinary Magisterium the following must be true:

1) the teaching must be on faith and morals and apply to the whole Church and not just to a part of it (e.g., a teaching that applies only the Latin Rite is not eligible for infallibility status)

2) The Pope, or the Ecumenical Council of Bishops, must specifically propose the teaching as infallible

3) For a ex cathedra proclamation the Pope must declare the teaching, with the two requirements above, as the universal pastor of the Church. (he does not have be physically on the papal throne).

Or, when an Ecumenical Council of Bishops wishes propose a infallible dogma, the Pope must ratify it.

In addition to extraordinary Magisterial declarations of defined dogma discussed above, a teaching can be infallible by the Ordinary Magisterium. These are teachings that have been passed down from the early Church (e.g., the evil of prostitution is an infallible teaching but not because any pope or council formally said so. It is an infallible because that is that has always been taught by the light of divinely revealed truth.)

This "definitive" teaching must be believed by the Catholic. As then Cardinal Ratzinger, in his commentary of the change in Canon Law promulgated by Pope John Paul II in Ad tuendam fidem, entitled, Doctrinal Commentary on the Concluding Formula of the Professio Fidei, said concerning definitive teaching:

The object taught by this formula includes all those teachings belonging to the dogmatic or moral area, which are necessary for faithfully keeping and expounding the deposit of faith, even if they have not been proposed by the Magisterium of the Church as formally revealed.

Every believer, therefore, is required to give firm and definitive assent to these truths, based on faith in the Holy Spirit's assistance to the Church's Magisterium, and on the Catholic doctrine of the infallibility of the Magisterium in these matters. Whoever denies these truths would be in a position of rejecting a truth of Catholic doctrine and would therefore no longer be in full communion with the Catholic Church.

For a discussion is a previous Q&A see, Four Levels of Church Teaching.

God Bless,
Bro. Ignatius Mary