Bishops and Cardinals are infallibly-correct (though not personally infallible)
when teaching IF they are teaching the DEFINED TEACHINGS of the Church,
for those are already settled,
either by an ECUMENICAL COUNCIL gathered in the Holy Spirit, concluded and
solemnly Confirmed by the authority of the Successor of Saint Peter, the Bishop of Rome, the Pope. An Ecumenical Council **confirmed by the pope **has, in it’s doctrinal definititions, the same authority as a solemn Papal Definition made by the Pope alone
((such as of the Assumption of Mary, always taught at first implicitly in the earliest church and then explicitly for 1500 or more years PRIOR to the Pope’s 1950 Definition)).
This is because, when all the Bishops of the Church, the shepherds appointed by the Holy Spirit, assemble IN the Holy Spirit, united to the approval of their definitions by Peter’s Successor, an office also protected by the Holy Spirit, they cannot define as true something that is Erroneous.
WHAT they define will always be TRUE, BUT it may need further explanation at a later date, say centuries later, when later Catholics misunderstand the “point” of what they were trying to say. “No Salvation Outside the Church,” for example, is being taught by modern sedevacantists as meaning that only baptized Roman Catholics have any chance at all of being Saved and that everybody else, no matter who or no matter why they are not officially Catholics, are automatically Damned up, down, sideways and backwards.
Vatican II Correctly clarified what is the correct sense in which this teaching should be understood.
Popes only define a doctrine, unilaterally, when it is absolutely necessary, in his estimation, to do so. Pope Pius XII didn’t wake up one morning in 1950 and
haphazardly decided, on the spur of the moment, “Ya know, I think I’ll declare today infallibly that Mary was assumpted into heaven body and soul upon her passing from this life”.
No, he, and his predecessors, had been being bombarded for decades by millions of petitions from Cardinals, Archbishops, Bishops, Priests, Nuns, and Laity by the scads,
begging the Papacy to solemnly define the Assumption, which had always been the understanding and, for over 1500 or more years, the public teaching of the ENTIRE Catholic Church and of the Eastern Orthodox Churches as well (though they call it
Mary’s Dormition, it means the SAME THING). In response to this incessant flood of pleadings, the Pope took the matter to God in Prayer for years, as well as carefully researching the entire history of this teaching, in the East and in the West, and finally decided to affirm most solemnly, what Catholics (and Eastern Orthodox) had ALWAYS believed.
I had a friend, a Presbyterian who, obviously, did not believe in the assumption and thought it was something that the pope just made up one day on a whim,
snottily retort when I mentioned the doctrine that “Oh yeah, right, yeah, SUUUUUURE, yeah, so in 1950, Mary was SUDDENLY ASSUMPTED.”
We Catholics (and I was anti Catholic for most of my life, so I know this) very often have very little concept of just HOW nonCatholics think that our Catholic Doctrines have been arrived at. They really do think that we just make stuff up as we go.