Although sola Scriptura may be played at varying levels of sophistication, it IS a straw man. Even the cleverest exponent of the doctrine must eventually rely upon either Tradition or his own interpretation – always claimed to be the personal guidance of the Holy Spirit.
As one who believes
sola scriptura is a good doctrine, allow me to try express it properly. In order for
sola scriptura to be applied properly, one must understand severalthings. Primarily, it is that Scripture (both Old and New Testaments) were written to people of ‘high-context cultures’, which meant that things that would have been understood by men of common backgrounds (say Luke and the person he is writing his Gospel and Acts to, or Paul and the churches he writes letters to, etc.) are left unsaid. Modern American ‘low-context culture’ spoon feeds everything, even if it is mere repetition to the intended audience. Things that would be mentioned by a writer in a ‘low-context culture’ are left unwritten in a ‘high-context culture’ because it is assumed that said audience, with a common background, would already know said things.
The problem for the modern reader (or any reader existing in the Post-Apostolic period) is filling in those ‘contextual blanks’. Filling in those ‘blanks’ is a necessary part of
sola scriptura. To deny so, in my opinion, renders good exegetical interpretation of Scripture virtually imposible (barring Diving Revelation or blind ‘luck’ in the interpretive process).
What many people call
sola scriptura might better be described as Sola Scriptura Extremis, which J. P. Holding of Tekton Apologetics Ministries discusses
here.
Attempting to fill in these contextual blanks is usually accomplished through analysis of the following:
- Linguistic analysis (Hebrew, Greek and Aramaic do not translate perfectly into English or any other language and, for Hebrew and Greek, Biblical Hebrew and Greek are somewhat different from their contemporary variants)
- Contextual analysis (incl. textual, historical, social and cultural)
- Examination of previous interpretations (ECF, Reformers, Jewish [esp. for OT writings], etc.) and timely external commentary (Philo, Pliny, etc.) (timely external commentary to see what people witnessed Early Christians doing, etc.)
Obviously, this does not guarantee accuracy. After all, the Patristic and Pre-NT Jewish writings would have written within the framework of a ‘high-context culture’. This more nuanced method of sola scriptura seems also to require more patience (and also perhaps humility) than the ‘anything goes shot-in-the-dark’ method used by some well-known Protestants. In some ways, it would be nearly impossible for one person to do all this. After all, one maybe an expert in the Patristics, or Ancient Hebrew, or Roman history and culture, or a myriad of other things, but I have yet to meet someone who is truly all-knowing. The truly great modern apologists (and I would count J. P. Holding and people at Christian Think-Tank among them) have people who specialize in areas of knowledge (or at least have access to the writings of those with specialized knowledge) and they do not attempt to ‘go-it-alone’.
Perhaps Peter’s warning about prophecy being not of private interpretation should perhaps be applied a bit more to Scripture. The profit of sola scriptura is that it can promote each individual seeking a better understanding of Scripture and the faith, but the danger is that it can lead to laziness (people feel they need nothing else but their KJV bible), pride (people begin to think their interpretations of Scripture are the correct/best ones) and confusion (since so many people do put forth their private interpretations as factual, it makes it confusing to know who to believe).
Thus, it seems one is stuck between a rock and a hard place. The Roman Catholics don’t believe in it and many Protestants may believe it, but they sure don’t apply it properly.
Since Jesus and the Apostles used the Septuagint, which contained the deuteros, that is the source of all their quotes. 
