The "real" reason why sola Scriptura is untenable

According to Michael Liccione:

The distinction I’m invoking is important when dealing with sola scripturists, especially those of the Reformed persuasion. They typically hold that, at some point, we come to understand the semantic meaning of scriptural and confessional statements as well as they can be understood, which is supposed to be all that’s necessary for understanding the Christian faith. It is true that we often can and do reach such a point with scriptural and confessional statements themselves; when we do, that suffices for telling us what the statements mean as expressions of human thought. But of course it does not follow that that suffices for telling us what we ought to believe now. That question can only be answered by locating, identifying, and submitting to the authority by which such statements are propounded. Hence, when dealing with those who uphold the “perspicuity” of Scripture, we can readily grant that, in many instances, Scripture is perspicuous enough to tell us what its human authors meant. The same goes a fortiori for creedal and other confessions. But without some further account of authority, that does not suffice to tell us all that we ought to hold as de fide, or even why what they meant even is de fide.

http://www.calledtocommunion.com/2010/11/sola-scriptura-a-dialogue-between-michael-horton-and-bryan-cross/#comment-12734

i) This objection drives a wedge between divine and human intent. Yet the human intent of the Bible writer is divinely inspired. God inspired the authorial intent of the Bible writer. It is therefore fallacious to oppose divine and human intent when human intent amounts to inspired intent. For God expresses his intentions through the intentions of the writers and speakers he inspired to write and speak in his name.

ii) It sounds as though Liccione is operating with a theory of partial inspiration, whereby it’s necessary to winnow the Scriptural statements we’re supposed to believe from the chaffy statements we are free to disregard.

iii) In the meantime, notice his fatal concession. He admits that we can arrive at a correct understanding of the text without the services of the magisterium.  

This is why there’s no getting round the question by what authority Scripture is to be accepted as a record of divine revelation, and by what authority it is to be interpreted as containing what we ought to believe. The authority questions remain even we reach an upper limit of linguistic explication. That’s the real reason why sola scriptura is untenable.

i) Well, if you wish to cast the question in authoritarian terms, then we accept the revelatory status of Scripture on the authority of the very God who revealed it.

ii) But why cast the question in authoritarian terms? Why not recast the question by simply asking how we know the Bible is the word of God? We can know many things without recourse to some “authority” or another. Why make “authority” the default condition for knowing what is true or false?

iii) If the Bible is plenarily inspired, then it’s incumbent on you and me to believe the whole thing. We don’t need an extrabiblical authority to isolate and identify which statements contained in Scripture oblige our belief–in contrast to other Biblical statements which don’t. Liccione is creating a false dichotomy.