In a blog post a week and a half ago, Peter Leithart addressed the issue of Sola Scriptura in relation to Christian Smith's recent book How to Go from Being a Good Evangelical to a Committed Catholic in Ninety-Five Difficult Steps. His defence there of sola Scriptura rightly understood was solid stuff, emphasising the importance of distinguishing between Scripture as sole authority and sole final authority. Tradition may be a very important authority, may even be a guide to the interpretation of Scripture, but when the chips are down, tradition must always be revisable by Scripture, in a way that cannot be vice versa. This line of argument is a reasonably familiar one, and yet it seems to me that there are really two distinct issues that have to be addressed when we are talking about sola Scriptura--the "intensive" question and the "extensive" question.
The first concerns the "strength" of the sola--just how alone is Scripture, and how much is it aided by tradition? What respective roles do the two play in establishing the rule of belief, and how much can each one do taken by itself? The second concerns the scope of the sola--just how broadly does it reach? On just how many issues are we claiming Scripture's authority? Is Scripture the authority over, say, mathematics? This is the sort of idea that gets R2Kers all worked up. Leithart's notion of "final authority" is of course of some help here, for this allows that other authorities can command our respect in this field as much as they want, so long as they do not contradict Scripture, which, given how little Scripture has to say on the subject of mathematics, will be pretty rarely, if ever.
This was of course how the Reformers explained the doctrine, according to their distinction between "things necessary for salvation" and "things indifferent." In things necessary, Scripture is the only authority; in things indifferent, it is the final authority. Which means that, if Scripture is silent on a subject, you can believe whatever you want to, so long as you don't say that it is necessary for anyone to believe thusly. (At least, in theory that was the doctrine; pretty soon Protestants were saying that it was necessary not to believe in or do any number of things about which Scripture was silent.)
This qualification also applied to the Reformation's notion of the "perspicuity of Scripture," a concept that has been much misunderstood and misused today. The perspicuity of Scripture meant that God did not leave us so little guidance in His Word about the path of salvation that we needed other authorities and other information to repent and believe and be saved. All the essentials, the bare necessities, were there in Scripture clear enough for the lowliest peasant to comprehend and act upon. Of course, there were many matters in Scripture not so clear, and open to dispute; but the fact that they were so, according to the doctrine of perspicuity, was conclusive evidence that these were not matters necessary and essential.
This, I take it, is the point on which Protestantism (or the varieties of it with which I am familiar), has veered so dangerously off-track, inciting a reaction away from its fractious dogmatism that often takes the form of a rejection of sola Scriptura altogether. For, if one applies the doctrine of perspicuity too broadly, then potentially any doctrine can become the article of a standing or falling faith, potentially any doctrine can be a legitimate occasion for schism, since "it's a matter of the authority of Scripture." If, for instance, I am convinced of Calvinism, and I am convinced it is demonstrated in Scripture, and I am convinced that Scripture is perspicuous, then if you reject Calvinism, this must be a rejection of the authority of Scripture. It couldn't be a difference of interpretation or application, since Scripture is clear. Therefore, it must be because you refuse to accept Scripture's authority. Therefore, you have abandoned the material principle of the faith, and are on the brink of apostasy. So the argument could run (although I'm not sure that's how it has generally run in the case of church splits over Calvinism, which have usually proceeded on even more dubious theological logic).
It is this theological breakdown that has contributed to the vitriol of recent debates between "liberals" and "conservatives," and that distinguishes such recent debates from their counterparts a century ago. Back when Machen left the PCUSA, it was, ostensibly at least, because the deity, resurrection and exclusivity of Christ were being rejected or at least quietly abandoned. Nowadays, our great church splits and controversies occur over issues like Young Earth (or even Six-Day) Creation, women's ordination, and homosexuality. Now clearly none of these issues concern in themselves the essentials, the Gospel (although if one is Catholic, women's ordination raises extremely serious issues about the apostolic succession, validity of the priesthood, and therefore ability to receive the means of grace--and so, presumably, affects salvation; and on the Creation issue, one can argue that the evolutionary narrative would have domino effects on key Christian doctrines that would ultimately undermine the Gospel). And yet in many quarters, one, two, or all of these are considered make-or-break issues? Why?
The rhetoric is clear enough most of the time--"It's a matter of the authority of Scripture!" Perhaps these "liberals" don't reject the deity or resurrection of Christ, but they're rejecting the Bible, and these other doctrines are thus sure to fall by the wayside soon. Scripture, we are told, is clear on these points, and therefore, there is no way to deviate on these points without openly flaunting Scripture. By this means, each of these issues, and potentially any number of others, can become automatically just cause for a breaking of fellowship.
But of course, we can't be so quick to dismiss this as a failure to distinguish between things necessary and things secondary. Because that distinction does not map straightforwardly on to "things clear in Scripture" vs. "things not clear in Scripture" (as Hooker sometimes seems to imply). Obviously, there are plenty of secondary, indeed, plenty of completely unimportant things that are quite clear in Scripture. For instance, that Paul spent three years in Ephesus. Does it matter? Well, not really. But since Scripture seems clear on the subject, then how do we respond if someone were inclined to deny this fact? Presumably this denial (or pick your own crystal-clear example) would be a matter of great concern.
So then, I suppose, what this distinction forces us to do is ask again whether the matters debated really are so crystal clear that to reject them is to reject Scripture, instead of simply assuming that they are.
Of course, it is also worth noting that some issues currently under debate, particularly the Creation issue, also pertain to what I have called the intensive authority of Scripture, and perhaps raise similar questions to those of the relationship of Scripture and tradition that proved so crucial at the Reformation. For what we are now forced to ask is whether Scripture can stand on its own, or whether we need to listen to the testimony of Scripture and science (or, Scripture and historical studies) together in order to find truth, whether science must function as the interpreter of Scripture on certain points in the way that tradition once claimed to. For many, yielding an inch to science to science seems like a rejection of sola Scriptura. But could we apply Leithart's same logic here--science may exercise authority over our interpretations, so long as Scripture remains the final authority, in light of which, if push comes to shove, science must be revised and not vice versa?
All of these are but musings, thinking aloud, so to speak. How they all fit together, and cash out in practice, I'm not at all sure, and I'd welcome any input.