There is a very common objection, from Roman Catholics and Orthodox, to the doctrine of sola Scriptura: it makes each individual believer the official -- and potentially infallible -- interpreter of Scripture. For some Protestants, of course, this is true. It was true in my case, at any rate. I remember a student, who is now a relatively well-known Lutheran apologist, talking to me once about my views on justification. He asked how I could hold a certain position, since it didn't seem to jibe with the Westminster Confession. My response, which was the same I gave my pastor at the time, was that I didn't particularly care if my interpretation lined up with the WCF, as that was a human produced document of only relative authority. Rather, all I cared was whether or not my understanding agreed with Scripture. What I didn't realize at the time was that I had made my own reason, and investigative powers, the benchmark of interpretation. I was not necessarily any closer to what Scripture actually meant, but I was very close to what I meant. This is not to say that my baseline critique wasn't valid, it just didn't go far enough.
Let me explain.
There is no reason to believe that my researches in history, philosophy, textual transmission, or even theology would lead me to a particularly proper interpretation of Scripture. Using the historical-grammatical interpretive method (and this could be applied to most other "critical" methods) actually leads us into a quagmire: if we cannot understand the Scriptures without detailed analysis of the history and language behind them, then we will never truly understand the Scriptures. Both fields, linguistics and archaeology, are fraught with human interpretive foibles. Not to mention that those communities who, historically speaking, have not had access to decent scholarship are therefore put in an unenviable position: they may believe, but they cannot fully or truly believe. They are relegated to an impoverished state in the Church. (This is also a problem with holding that inspiration stops with the autographa, or original documents from the Apostles and Prophets -- they don't exist anymore, so any copy of the Scriptures is potentially riddled with errors; how can we confidently know what to believe, especially with scholars like Bart Ehrman telling us that the communities in charge of the manuscripts have emended them to suit their particular ideological needs?) Not only this, but the sort of biblical interpretation as rational, scholastic endeavor means that those unable to engage on that level (children, the mentally handicapped, the uneducated) cannot fully benefit from the teaching of the Word of God.
To get around some of these individualist difficulties, there is the option to be a confessionalist: that is, the baseline interpretation of Scripture, at least theologically, is found in the WCF or the Three Forms of Unity, etc. (There still is the option for grammatical-historical work here, of course; but at least it has boundaries around what is and isn't possible to ascertain from the texts themselves). This does lead right into debates about how to interpret these documents and the various positions of "strict" v. "moderate" subscriptionism. Supra- or infra-? Paedo- or credo-? And so on. However, this isn't the problem that I had/have with the confessions. That lies in the actual authority of them. The reason my denomination holds the Confession in high regard is due to the belief that they are an accurate interpretation and application of Scripture. But, who gets to decide that? The authority of any confession becomes, quickly, circular. "We believe the Confession to be adequately interpreting of Scripture; why do we believe this? Because Scripture rightly interpreted produces the Confession." This is, of course, a gross over-simplification of the issue; but the point remains. As I've argued before, there is no "plain, clear, obvious" reading of Scripture. Each reading arises out of a certain theology, out of a regula fidei that is necessarily foreign to the Scriptures themselves (in other words, there is no such thing as solo Scriptura). The authority of the Confession, then, is a presupposition that cannot be adequately verified: it is an authority because it is an authority. It reminds me, rather, of the Anarcho-Syndicalism scene in Monty Python's The Quest for the Holy Grail.
Both ways of engaging in sola Scriptura, the individual, academic route and the confessionalist route, both fail to provide an adequate authoritative base. Both, in the end, must succumb to a form of fideism: we believe this to be the interpretation of the Scriptures because this is what we believe. Maybe, in the end, this is where, epistemologically speaking, we must end up. I hope not.
Again, the question becomes: where is the Spirit? If there is any theme that runs through my thinking, it is this. If we want to properly interpret the Scriptures, that is, if we want to read them towards the goal of salvation, then we must read them with and in the Spirit. This assumes, though, that the Spirit is an actual reality (Gr: hypostasis) and not just a cipher for an emotional state. We cannot say that we have the Spirit, and so are interpreting Scripture rightly, based on how we feel or on the presence of ostensible charismata, as both of those things can be engineered or manipulated (not just by preachers, but by our non-corporeal enemies). How do we know who has the Spirit, then?