As a card-carrying evangelical, one would think that sola scriptura would be right up my alley. Other Christian groups might want to bring in other sources of Christian understanding, but not us. A man and his Bible, it's a beautiful thing, eh? We need nothing else, so we say. I am humbler about that now. I liked that emphasis of Luther's when I was a Lutheran, but even he stepped slightly aside from it, as far back as the Diet or Worms. "Show me through Scripture or right reason..." he said. Well, the fundies would say that he'd given away the game right there. Given what has happened with the Lutherans in the 20th C, and now in the 21st, maybe sola scriptura is not so reliable. We'll come back to that.
The Episcopalians have the three-legged stool of Scripture, Tradition, and Reason. As"reason" now includes not just logic, but intuitive reason and experience, fair-sized trucks not only can be driven through this, but have been driven through this. Roman Catholics, much to the dismay of Protestants, value tradition so highly that it may exceed the authority of the Scriptures, in practice if not in theory. The eastern Orthodox are big on Councils to go with Patriarchs. Also very nice, though it has led to cooperating with every tyrannical regime that comes along. Worrisome. The Methodists have their Quadrilateral, adding in Christian experience to the Anglican three.The Presbyterians have not only Scripture, but Calvin's Institutes on their menu.
My own denomination, the Evangelical Covenant Church, has a tradition of two anchors "Where is it written?" and "How goes your walk?" I have found both to be excellent - for the first I can easily imagine old Swedes shouting it from the back of an annual meeting. For the second, it is not only a declaration that how one's relationship with Christ is proceeding is of equal importance to understanding the Scriptures, but also an invitation for each of us to share what is happening in our spiritual growth. Yet even this has been fraying recently, as both poles have been bent slightly.
Again why do I not then insist on Bible alone? Isn't that the only way home at this point? Aren't all these additional authorities the problem, rather than the solution? No, the Bible-only attempt turns out to be more dangerous in the end. If we say that we are going only by the Bible, we deceive ourselves, and the truth is not in us. We sit atop an iceberg and declare there is nothing beneath the surface. We swallow some part of the culture around us whole, not knowing.