I've done a quick skim through your comments here. It's obvious that you consider the Scriptures an infallible authority, and you also believe that the Roman Church (or however you want to put it) is an infallible authority.
My question to you is probably too simple compared to all the other interactions you're having at Green Baggins. I'd like to know, other than using the Bible, how do you establish that this other authority is also infallible? Or is it simply the case that you believe the Scriptures, correctly interpreted, establish the other authority? Above you appealed to Matthew 16 and 18 ("..in relatively few circumstances, perpetual infallibility. This comes from Jesus Christ as recorded in Scripture in Matthew 16 and 18"). In other words, when all is said done, is your primary way of establishing this other authority simply an appeal to Scripture alone?
But if this is the case, it appears to me to get a bit circular. The testimony of the Scriptures proves the infallible authority of the Roman church, but then the Roman church says the authority of the Scriptures is proved by the Church (Recall the favorite of all Roman arguments about determining the canon).
Of course you could say infallible sacred tradition establishes the other authority, but well, that's a bit like appealing to Bigfoot, as it can't really be pointed to ostensively. It's this murky thing, that depending on which Roman Catholic one talks to, means different things. Then the question becomes similarly, how do you prove infallible sacred tradition without appealing to the Bible? It goes in the same circular way: sacred tradition proves the infallibility of the church, but the church determines what is sacred tradition.
On the other hand, if you just want to say you begin with a basic presupposition (a faith claim) that both the Bible and the Roman Magisterium (and Sacred Tradition as well I guess) are infallible (like, sort of a VanTillian approach), well, there's really no point for anyone to dialog with you. You say it's multiple infallible authorities, we say it's one. All the interactions at Green Baggins become really... a waste of time.
I assume that perhaps there's maybe an answer you may have that I haven't quickly considered. I've always kind of thought that people who abandon sola scriptura ultimately simply just decide to to take on another infallible authority, sort of like how someone converting to the LDS gets a burning in the bosom.
When all is said a done, any appeals you make to Scripture to establish your other infallible authorities requires a lot to be read in to those verses (as proved above by Tfan). You can continually say that the Biblical evidence provided to you do not establish sola scriptura, but using Scripture in response to say it somehow clearly establishes other infallible rules of faith doesn't fly.
By the way Scott, thank you so much for defending some of the Reformers:
“…no one may knowingly reject any defined Catholic dogma, period. If I were unaware of the fact that the Assumption of the Blessed Virgin Mary were infallibly defined in 1950, and denied it – my denial would be rejected. If then I was made aware of the definition and continued to reject it, then I would be excommunicated.”This certainly covers Luther’s understanding of justification and the canon.