This post is one of a series introduced in the first and last paragraphs here. That should explain why it might be kind of weird.
As an evangelical Protestant I have been raised on the belief that what sets us apart from the other wings of the faith is our doctrine of Scripture. I no longer believe this to be true, except as a distinction between evangelical Protestants and liberal Protestants. At least on the basics (and perhaps more), however, we share the same doctrine of Scripture with the Catholics and the Orthodox; we agree completely that the Bible is the authoritative, true, reliable Word of God. What we do not share is a single doctrine of tradition. That's what sola Scriptura really is: not a statement about Scripture but a statement about tradition and its relationship to Scripture.
The evangelical doctrine of tradition is that there is a thick, bold, dark, sharp line between Scripture and everything else (i.e., the tradition of the church). Scripture in its entirety is God-breathed; tradition isn't. Scripture is entirely self-consistent and true; tradition isn't. As a result, evangelicals range from the near extreme of positive interest in tradition as a set of voices of some benefit but which may be easily dismissed if we don't like what they say to the far extreme of suspicion or even hostility toward tradition. (One could even look beyond the far extreme to heresies with evangelical roots such as the Mormons, who reject all orthodox tradition after the apostles, including the Council of Nicea, and replace it with their own tradition, the bulk of which is not framed as tradition but as more Scripture—the Book of Mormon.) There are, however, serious inconsistencies between the evangelical doctrine of tradition (which of course is never labeled as such) and evangelicals' practice. One is a fiercely loyal adherence to the content of the first four ecumenical councils (even if the creedal molds in which it is cast are suspect to some), which of course is tradition, not Scripture. Another is fiercely loyal adherence in some circles to Reformation and post-Reformation tradition—e.g., the Westminster Confession—which is merely a substitution of newer tradition for the older one and which looks in practice exactly like the Orthodox doctrine of tradition (see below) no matter how much its devotees protest that their tradition is subordinate to the Scriptures (technically the Orthodox do the same).
The Roman Catholic doctrine of tradition is that there is a line between Scripture and tradition (albeit not as bold and dark as the evangelicals' line)—the two are distinct. Nevertheless, both sides of the line are directly from God, entirely self-consistent, and entirely true and reliable. Neither has priority over the other. Further, Scripture and tradition are entirely in harmony with each other, so an interpretation of Scripture that violates the tradition is a misinterpretation of Scripture, and a refutation of tradition on Scriptural grounds is also a misinterpretation of Scripture. Consequently, although in theory the two streams (like a separate hot faucet and cold faucet in the same sink) are equal, in practice tradition dominates Scripture because (also in theory) for a tradition to become traditional it must have been rightly derived from the Scriptures in the first place. (Note how similar was the Pharisees' doctrine of tradition, which Jesus refuted—the written law and the oral, both supposedly having been received at Sinai by Moses, but in which the latter practically trumped the former.) What also must be noted about the Catholic doctrine of tradition, of course, is that while tradition is derived from the fathers and doctors of the church, it is defined by the Pope and/or church councils. (Historically—and perhaps today—the relationship between church councils and the Pope is complicated.)
The Orthodox doctrine of tradition is that while there probably is a line between Scripture and tradition, it is thin, faint, and fuzzy. Functionally the fathers are simply the New Testament Continued. Unlike the Catholics, who have a Pope to define what teaching makes it into the tradition and what does not (either because the teaching is wrong or because it is speculative and not certain enough to anthematize those who disagree), the Orthodox operate by a sort of consensus of reverence toward those who by corporate custom fall into the hallowed college of the holy fathers, especially viewed through the lens of the ecumenical councils. The totality (or at least generality) of the output of all of these fathers is regarded essentially as Scripture itself is regarded: as internally consistent, true, pure, and God-breathed, particularly about those matters that the Orthodox consider to be particularly important (e.g., Christology). To the Orthodox, the tradition is the tradition of the fathers’ right interpretation of Scripture, and so the idea that Scripture and genuine tradition would ever conflict is inconceivable. Thus, the Orthodox articulate, defend, and refute doctrine essentially the way evangelicals do, except that the former's "Bible" is much larger than the latter's. If there is one problem with this doctrine of tradition that jumps out to me as an evangelical, it is that if the biblical interpretation and theology of the fathers is that important, then why was it so important to those very fathers to define the biblical canon with precision? Clearly they believed that there was something truly unique about the biblical corpus, a uniqueness that is threatened if not lost altogether in the expansive Orthodox doctrine of tradition.
What is perhaps most interesting about the relationship of Scripture and tradition over the course of the church's life is that tradition became more important as heresy became more sophisticated. Early heretics in one way or another denied Scripture outright (most notably Marcion) or marginalized it in some other way (the Gnostics with their arcane interpretations and presumably the later Montanists with their obsession with charismatic prophecy). But later heretics fully accepted the concept of Scripture's truth—bald, uninterpreted Scripture was insufficient to arbitrate between Arius and Athanasius. So tradition—the words of the fathers, the piety and liturgy of the people, and the apostolic succession of the churches and their bishops—became increasingly important to point out the true biblical interpretations and syntheses from the false ones. Looking back, it is easy to see how the relative importance of Scripture itself declined and how that of the tradition of interpreting, synthesizing, and practicing the Scripture rose. One feature of the Protestant Reformation that was so radical was the Reformers' conviction that the mix of Scripture and tradition had gotten totally out of hand—by analogy, it was as if there was now so much air in the combustion chamber that there was no longer enough fuel there to cause an explosion. The Reformers' response, especially within the Radical Reformation, was to eliminate the "air" of tradition entirely and flood the engine with the "gas" of Scripture to set things right. Naturally, the Catholic Church reacted in an entirely predictable, opposite way. As it had for centuries against increasingly biblically loyal and sophisticated heretics, it relied on tradition to carry the day. What it failed to grasp (at first) was that now the tradition itself was directly under attack, not obliquely as in the past, and that the traditional interpretation and synthesis of Scripture had over centuries become so detached from the Scripture it claimed to interpret and synthesize that it could no longer hold up under critiques from Scriptural premises. By the time the Church regrouped, its knee-jerk reaction had excommunicated a third of Western Europe; the genie was out of the bottle and would not go back in.
In order for the three great wings of the faith—and perhaps the un-Orthodox churches of the East as well—to become visibly one, it is absolutely crucial to confess jointly one doctrine of tradition. In fact, it is so crucial that it may actually dwarf all other issues by comparison, which is no small thing given that the other issues include the Filioque, the papacy, and justification by faith alone among others. But an ecumenical doctrine of tradition may be the only door through which these other issues may be satisfactorily addressed. All communions need one, because each of our doctrines of tradition are flawed, perhaps more than I know. But by far the largest obstacles to an ecumenical doctrine of tradition are our traditions—that is, the traditions whose mutual incompatibility fractures the Great Tradition. To give a concrete example, it is highly unlikely that I can adopt a doctrine of tradition other than the evangelical one and keep my Baptist tradition intact, because any doctrine of tradition that makes tradition even a little bit more normative than it is for evangelicals will allow that tradition to nullify most of the features of my Baptist tradition (e.g., the insistence on believer's baptism). In effect, my tradition and thus my identity within the tradition cease to exist. The ecumenical doctrine of tradition, whatever it is, will entail painful sacrifice for everyone who embraces it—frankly, more sacrifice than I think any of us can bear.
But if we are to arrive at a new doctrine of tradition—at least one that I could find palatable at any rate—a few concepts that seem evident to me right now must influence the dogma. One is the acknowledgment that tradition doesn't always come into being the way we would like it to. (Of course, this implies that tradition "comes into being" at all as opposed to eternally existing, which may pose a serious problem for the Orthodox.) I always believed that in the annals of church history, people acted (worshiped, prayed, organized themselves, etc.) according to what they were being taught, what they confessed. And sometimes things do happen this way; for example, the radical liturgical (even architectural) changes of the Protestant Reformation followed directly from Reformation theological principles. But in the annals of church history just like in my humdrum experience today, it often goes the other way around: people act in particular ways and then a theological justification from Scripture for those actions arises ex post facto. (I find pneumatological responses to the experiences and worship of the Pentecostal and charismatic movements to be a telling modern example.) Sometimes this ex post facto theologizing works great, because the actions of the people are Spirit-led and on-target even if the people can't clearly articulate why—for example, how the ubiquity of prayers to Christ helped defeat Arianism. In situations like this, the actions of the church shine light on previously overlooked truths of Scripture. But other times ex post facto theologizing is a big mistake—that's how the doctrine of purgatory came into being, for instance, not to mention adoration of icons. In these situations, the actions of the church run counter to Scripture and carry the dogma of the church along with it. A proper doctrine of tradition must acknowledge the occasional fallibility of received tradition by insisting that true tradition always allows truth in Scripture to shine forth; it never obscures the truth of Scripture by merely pointing to other tradition. This is the evangelical contribution.
Secondly, a proper doctrine of tradition must take into account the role of heresy in clarifying the dogma of the church. The Scriptures contain all necessary truth for our salvation explicitly or implicitly. True tradition makes what is implicit in Scripture explicit (another way of saying "allowing truth in Scripture to shine forth" above). Heresy is usually what drives the church to do this. It usually takes a long time. By the early fifth century, the only doctrines that were really nailed down with precision were the Trinity, the two natures in Christ (and in the East this wasn't even finished), and the corpus of the New Testament. Other doctrines were taught of course, often accurately, beautifully, and powerfully. But they didn't require the corporate clarification that the former did, so mutually incompatible diversity on some doctrines and unquestioned assumptions in others (such as baptism?) continued to float around. A proper doctrine of tradition says that this is okay. It states that we have been given everything we need to know in the Bible, but it takes us a really long time to figure out just what we've been given. Thus, the faith is indeed "once for all delivered to the saints," but it takes a long time and many hands to unwrap the package. It also means that elements of the tradition in the "unquestioned assumption" category don't have to be considered part of the true tradition. If the fathers (for example) never had reason to question their agreement on how to view Doctrine X, then their agreement is not normative. It is not until after a question has been opened, usually by heretics but sometimes by the saints (such as Augustine's theory of double predestination?), and vigorously thrashed out that a normative agreement can be reached.
Finally, perhaps the stickiest methodological issue pertaining to a doctrine of tradition is, what are the authoritative sources of such dogma? Obviously the only authoritative source is the Triune God. But is the medium of the Holy Spirit's revelation the Church of Christ—i.e., the tradition held by the Orthodox and/or the Catholics? If so, is dogma derived this way fatally self-referential? It is even worse for evangelicals counting on the Spirit's revelation through the Word of Christ, the Bible, for does the Bible have the necessary material to construct a doctrine of what followed its completion? Perhaps it does, but this is a new investigation for me, so I really don't know.