I find these arguments about the "weakness" of Sola Scriptura to be weak in themselves because they presume that there's a solution by simply adding another infallible authority or authorities to the mix.
Let's take Abraham, as an example. What authority was he to appeal to, outside of what he received from God, to validate that God's Word to Him was the sole rule for faith and life?
The man had an encounter with the living God. It was not an encounter with a set of propositions that he decided to lend credible authotiriy to it and thereby lend it real authority.
The point with the Scriptures is that they are breathed out by God. They are, by their very nature, authoritative because they come from the mouth of God. Nobody lends to them credibility or authority. God needs no man to grant them status as His Word.
These questions arise primarily because people think in this way: How can I, by my autonomous reason, take in the facts of the case and decide what I'm going to lend ultimate authority to?
Or it will proceed along these lines: How can the Church, using its own historic and philosophic investigation, decide what Scriptures it is going to lend infallible authority to?
The persons who start in such a manner have already revealed they don't believe the Scriptures. Why? Because it is the Word of God that creates the Church to begin with. God called Abraham, Isaac, and Jacob and made them a people by His Word. He established the Church in the desert and in the land and governed them by His Word.
People like to assume that the Church creates the Word but it is the other way around.
There is also an underlying problem of "how do I know" that belies unbelief that the Spirit is not active in the Church. People either don't believe the Spirit is at all at work or, if He is, He is only interested in personal salvation and not in establishing people in the Word. He could not possibly play any role in speaking to His Bride! No, the Bride of Christ, by many folks' schema, receives no help from the Spirit in order to recognize the voice of Her Bridegroom.
Let the detractors come. God, alone, breathes out His Word and He has not left the Church without the Spirit in order to help her know what the Word is as well as to be illumined by it. Rome can sputter blasphemies all she wants about being an infallible source but, until she demonstrably proves that God ever revealed to men that He would keep His Church from error, then I remain fixed upon the point that He has preserved from error. It's faith in God and not in men. If that's not intellectually satisfying then I think the problem is not one of truth but one of trust.
