Once upon a time, RL asked a very pertinent question. Unfortunately, I completely missed it at the time. Therefore, in accordance with my glacial writing speed, here’s the extremely late answer.
Well, ok, perhaps I should post the question first…
“Where are the boundaries outside of which I must not stray, and what are the positive propositions which I must accept? That's the question, put more polemically than I could wish.”
This question comes up often, but is phrased a little differently: “What do I have to believe to be Catholic?” There are two ways to answer this. First is the simple method of giving a couple of sources that explain the specifics of what we Catholics believe. The second goes a bit further – ok, a lot further – and will require some explanation.
The First Part
The Catechism of the Catholic Church (CCC) is the official teaching of the Church in a single volume. It is here that you can get all the details and most of the supporting information. For example, in one section you might get the actual words used by the Magisterium (through the pen of John Paul II). That section may come with footnotes that refer to other Church documents. These other documents could be from Vatican II or Trent, or could be scriptural quotations, or notes to the Code of Canon Law, or the doctors of the Church, or a variety of other places. The Catechism is an impressive work in that it is so complete.
Now, Jimmy Akin recommends that people read it cover-to-cover. I’ve never managed that myself (which explains why Jimmy gets paid for this and I don’t). I use the CCC as a reference book. Either way, the whole story is there. I only point this out to say that, at 900+ pages, the CCC can be used in whatever way works for you.
A second resource in this vein is Fundamentals of Catholic Dogma (FCW), by Dr. Ludwig Ott. Be forewarned, FCW is a bit dated. It was originally printed in 1953. My copy was last updated in 1960. It does not, therefore, come with references to Vatican II or the likes of Humanae Vitae. That’s not such a big stumbling block as you might think, but it is something to keep in mind.
FCW covers everything in a thematic format. It’s almost 550 pages of rather small print (I have to wear my reading glasses for this one). It’s very well indexed and a breeze to use. Ott is also a very plainly honest scholar as well. I’ve actually had this book used against me as a weapon (figuratively…though at 550 pages it could be used literally, I suppose), and Ott’s honesty was part of the issue. For example, Ott says at one point (p 360), “The validity of child-baptism cannot be proved with absolute certainty from Holy Writ, but it can be indicated with a high degree of probability.” Ott then goes through a lengthy discussion of the subject. (And I'll go into an even more lengthy discussion when I get to the sacraments, but that's a bit down the road and baptism won't be the first stop along the way.)
For some things, you simply won’t find a quote in the Bible that says what you want in a point blank manner. Ott doesn’t shy away from these issues. Instead, he takes them on and gives the support for each element as expressed in a variety of ways, from Church documents, to councils, to papal statements, etc.
FCW is dry and can be a slog, but it has just about everything you’ll ever want to know (in print too fine to be comfortable).
Ok, so the CCC and FCW are the easy answers.
The Second Part
This is where things get a bit more complex. It’s not a matter of complexity, but of understanding, so bear with me while I try to figure out how to say this properly.
I’ve said many times here, and will probably say again, that conversion to Catholicism is both an intellectual and emotional process. You have to, at some point, wrap your head around the ideas behind the teachings, but you also have to follow your heart and the guidance of the Spirit. If the balance isn’t struck at some point then the conversion will be valid but perhaps a bit hollow. (At least, that’s my own personal opinion. You might get a different opinion on the subject from everyone you ask.)
The reason I put it in terms like his is very personal. My own conversion was lopsided. I followed the Spirit as He touched my heart. My head followed several years later. So, how did I reconcile the time between these two events?
I ended up in RCIA after a long struggle against the Spirit. I didn’t want to get religion, and Catholicism was the last thing I had in mind. However, over the course of years and years, the Spirit wore me down. After a time I recognized this, and surrendered myself to His will. It sounds more dramatic than it was, but these are the terms that come most comfortably to me today.
I got out of RCIA without knowing more than the absolute minimum. The parish I went to was pretty lousy at catechesis, and the priest in charge was all too willing to look away when someone wanted to hang onto their Protestant beliefs. Basically, I converted because I felt, not because I understood. It was faith that got me through this in a peculiar way.
Now, don’t freak out when I say this. Many Protestant’s I’ve known will dive off the cliff when they read the next sentence. At the time of my conversion, I placed my faith in the Church and I trusted implicitly that it would not lead me astray. Now, I hope that everyone reading these words will understand that this is NOT a faith intended to replace God in any way. But in reality it is faith nonetheless. This is what we mean when we say that we “have faith in the Church”, or that our “faith is in the Church”. Having faith in the Church – faith that the Church teaches the Truth whether I learn all that truth or not - is often a bigger leap of faith than the original leap that brought people to God in the first place.
I read something, once upon a time, that Scott Hahn wrote on this subject (though I can’t for the life of me lay my hands on the title just now). Hahn wrote something to the effect that Catholicism requires the highest level of Christian faith. Not only does it require the usual Christian professions of faith in God and the Cross, but at some level it also requires faith in the Church herself. Again, this faith does not detract from our faith in God.
Does this make sense?

The second part makes a great deal of sense, at least to me. To a Protestant who professes the Nicene Creed, and says he believes in one holy catholic and apostolic church, an implicit faith in the church is pretty much unavoidable. (The lower-case "c" in church in that sentence was deliberate, of course.) For folks in the free church traditions, it may be more of an issue.
The first part is more puzzling to me. I've not read Ott, so I'll pose the problem that I see in terms of the Catechism, which I've read pieces of, but not the whole. It seems that the Catechism is both more and less than a statement of the boundaries outside which a Catholic must not stray, or of the positive propositions he must accept, for his soul's health. There is much in the Catechism that is stated vastly differently than the same point of doctrine once was -- think, for example, of the famous section 2267 on the permissibility of capital punishment in the modern world, drawing on Evangelium Vitae. I doubt it could have been said that that was the Church's teaching half a century ago, and it is in any event framed as a prudential judgment that may well not apply if circumstances are today, or someday become, otherwise than Pope John Paul II perceived them. Does one who professes to believe everything the Catholic Church teaches necessarily profess agreement with that paragraph of the Catechism the way it's written?
The answer to that rhetorical question must be no, at least as I understand it. The Catechism both says more than the Church teaches -- for one may permissibly agree in only a qualified way with the statement as written in the Catechism -- and less -- for the next edition of the Catechism (whether published next decade or next millennium) may state the matter differently, and indeed so differently as to be nearly unrecognizable, or may omit the matter entirely for editorial reasons. And doubtless there are doctrines that are articles of faith, taught by the Church today to be divinely revealed, that were only theological opinions a century or two ago.
And of course examples could be multiplied. Think of the twists and turns that have surrounded the status of the Filioque in the Creed, or the meaning of extra ecclesiam nulla salus, or the appropriate term to describe the mystery of the Real Presence in the Eucharist. What the Church says today in its Catechism isn't necessarily congruent with what it said in its official teaching yesterday, and may not be congruent with what it says tomorrow. The Faith is simultaneously once delivered unto the saints and subject to development or unfolding, often in surprising ways that bear little resemblance to what went before. It's comforting to hear that what's said today isn't inconsistent with what was said a millennium ago, and won't be inconsistent with what's said a millennium hence, but the content of the Church's teaching still seems awfully protean. I think Fr. Neuhaus referred to this as the "blank check on your soul" problem.
There's some question of hierarchy of norms here, I suppose, and it may come down to a need to understand better what then-Cardinal Ratzinger was getting at in the CDF commentary on the Professio Fidei from 1998. It may well be misguided to ask for a list of propositions that form the boundaries. Certainly I couldn't give such a list of the boundaries defining my Protestant version of the Faith.
Hi RL,
Thanks for the lengthy comment. It helps me understand where you're coming from a bit better. I think I see where we're missing each other.
First off, I don't think I can answer your specific points in a combox exchange. I could never do them justice. However, there are answers to the specifics. I'll just defer to a later post where things can be expanded upon more.
However, I'd like to take a shot at a general answer and see where that takes us.
A distinction has to be made between doctrine and dogma. The two words are not synonyms. A doctrine is simply a teaching, a dogma is something that must be taken on faith by all Catholics. The distinction is often overlooked, but you can't make sense of Catholic history without it. (And make no mistake, I don't assume that this is going to be a comprehensive answer that will lay all doubt to rest. We're in generalities-land right now.)
Doctrine is discern-able. Because of this, a doctrine can develop over time and will develop based upon the guidance of the Holy Sprit. The move from burning heretics to the point of making it very difficult to justify state sponsored execution, is an example of doctrinal development that hasn't reached the state of doctrine...and may never reach that level. A dogmatic proclamation can be looked at as the end of the line in doctrinal discernment. The Spirit continues to guide the Church as she continues to search for the truth. The faith in the Spirit's guidance is also fundamental to Catholicism.
Lots of different subjects are generated by theologians contemplating God's revelation. Some examples might be limbo or women's ordination. Limbo has been contemplated since St. Augustine's time (maybe earlier). It became popular in the middle of the 20th century. After consideration, the “doctrine of limbo� was eventually dispensed with. Now, limbo was considered a doctrine by many people (hence the quotation marks). The problem is, it was never considered a doctrine by the Church herself, and it was certainly never raised to the level of dogmatic certainty. Ditto women's ordination. It was considered by theologians since the 1930's (I think it was the '30s). John Paul II set it aside so firmly that you might look at it as a dogmatic definition in the negative.
This gets to what might be a far trickier issue. How can you tell what's dogmatically defined and what's not? This is a far more difficult question, and one that I can't get at in a combox. (Sorry 'bout that, but I try to make sure that what I put on yon blog is accurate and has enough room to breath.)
I once got into a long and weird discussion with an Episcopal priest with regards to the Church's position on torture during the Inquisition. His contention was that the Church had once ordered torture against it's opponents, those orders had come from several popes, and the orders had come over the period of 150 years or so. His history was a bit foggy at times, but we'll look past that for the moment. His point was that the dogma is assumed by a long period of time and the idea that a pope had ordered torture. It just simply doesn't work that way.
Of course, torture as a form of legitimate judicial inquiry was never raised to the level of doctrine, much less dogma. This exemplifies, in an admittedly hyperbolic (and borderline bizarre) difficulty in getting at what is and isn't doctrine.
I think this gets to your question albeit indirectly. Unfortunately, my wife and kids are all looking at me with dangerous expressions. I gotta go or the daggers are gonna start flyin'. Ask some questions and I'll try to add more later.