Angelus,

Again, I have no problem with you or me proposing what we think are accurate and true definitions. However, when the hierarchy says, "we're indefectible in our teaching when we agree," or, "we're indefectible," and we are discussing whether that statement is true, providing our definition of "indefectible" doesn't test their credibility and whether what they say corresponds with "what's out there," i.e, passes the truth test - if we are not speaking about the same thing as them when they say, "indefectible."

I am looking for an agreed understanding of the term, an understanding of the term as used by the hierarchy,  and demonstrated by its approval of the definitions advanced for the term in approved Catechisms, approved theological manuals, definitions by the hierarchy itself (even better, as with the Vatican I fathers' definition I've referred to), commonly accepted Catholic Dictionaries . . . an understanding of the term accepted as the Catholic understanding.

DR

DR, if you think that the "indefectibility of the Church" means that any current group of men in the hierarchy can say "we're indefectible in our teaching when we agree," then I don't believe that you understand what "indefectibilty of the Church" means. 

It seems to me that you might be confusing "indefectibility" with "infallibility." Those words deal with different things. 

Indefectibility presupposes there is something to "defect from," in this case, the Catholic Faith (dogma) as it exists prior to any possible "defection." 

Infallibility is the idea that modifications or additions to the pre-existing tenets of the Catholic Faith (dogma) can be trusted as true because of the source (Pope or ecuмenical council) of those modifications and additions.

But infallibility can only occur within the context of indefectiblity. Otherwise, Jesus's teaching could be changed by the last Pope, and the next Pope could reverse him, and on and on.

The statement that you proposed seems to me to make sense if we substitute the word "infallibility" where you had "indefectibility." The new sentence would say, "we're infallible in our teaching when we agree." This agreement can be understood in a two-fold way. 

1. there is agreement of the Bishops and the Pope with each other in the results of a valid Ecuмenical Council.
2. there is the agreement (non-contradiction), of whatever those Bishops and Pope might newly define, with the prior Magisterium of the Church (including the Ordinary and Universal Magisterium).

Either way, there is a pre-existing deposit of Faith and Magisterial teaching that cannot be "defected from" by any new teaching. If those in the current hierarchy tried to propose a contradiction to previous settled Church teaching, they would be "defecting from" the settled Church teaching and, therefore, they would not be speaking as "the Church" because "the Church" is "indefectible." In other words, the true Church cannot contradict itself on matters that have been permanently decided (dogma).