(1) Sola Scriptura is Epistemically Useless in Determining the Canon of Scripture
Protestants define sola scriptura in various ways. Some say that Scripture is the only infallible rule of faith, while admitting non-infallible authorities such as tradition and the Magisterium. Still others focus more on the practical dimension of always checking ecclesiological doctrine with Scripture. Regardless of how one defines it, scripture itself never gives us a list of books that constitute “scripture”. So we have to appeal to some external authority to determine the canon of scripture, which necessarily excludes nuda scriptura (i.e., scripture as the sole source of authority). In determining the canon of Scripture, Lutherans historically appealed to tradition and the Magisterium, while Calvinists typically appealed to the interior witness of the Holy Spirit. I find it difficult to believe that the Holy Spirit would personally reveal to every Christian member the inspiration of each and every book of the protestant canon. Undoubtedly, the Holy Spirit plays an essential role in the corporate recognition of the inspiration of the canonical texts, but we neither find it implied in scripture or the tradition of the church, that the Holy Spirit will personally reveal to each and every member of the Christian body the particular canon of scripture.
(2) Sola Scriptura Inverts into Nuda (or Solus) Scriptura
Although most Protestants admit external, albeit non-infallible, authorities outside of the bible (such as tradition and the Magisterium), the underlying doctrine of sola scriptura, namely, the right of private judgment, inevitably ends up inverting sola scriptura into nuda scriptura. The doctrine of private judgment holds that a Christian may freely appeal to his/her own private interpretation of scripture to check and even overthrow the doctrinal pronouncements of the Magisterium. It should be noted that this argument isn’t primarily an epistemic question regarding the meaning of scripture, but rather the normativity of private judgments in relation to ecclesial authority. The question is who has ultimate interpretive authority? Scripture clearly indicates that Christ gave this authority to the Church, and not individuals. This is implied by the Church’s power of binding and loosing, which includes the power of excommunication.
https://energeticprocession.wordpress.com/2017/09/20/the-wizard-of-straw/
(3) Scripture Isn’t the Only Infallible Rule of Faith.
Although most Protestants admit that Scripture is not the only “rule of faith,” they claim that it is the only infallible one. However, if one accepts the infallibility of the apostolic college, we would have to posit another infallible rule of faith beside Scripture. Not only would a fallible apostolic college diminish the veracity of Scripture, it would also call into question the Christian faith itself. If the apostles couldn’t determine what authentic Christian doctrine was, I don’t know who else could. If one concedes the infallibility the Apostles’ oral teaching, then how do we know that their infallibility was restricted to them personally or that everything they taught orally was also written down? This seems to set up the possibility of the infallibility of both the Magisterium and Tradition. As long as there is a living and infallible teaching authority any definition of sola scriptura is necessarily false. The only route Protestants can take is by claiming that scripture became the only infallible rule of faith after the death of the last apostle. However, this is nowhere stated or implied in Scripture; especially when it would undermine the apostles’ own infallibility.
(4) Private Judgment Wasn’t Operative in the First Century
If the Apostles were infallible in their oral teaching then private judgment couldn’t have been operative in the first century. If the Apostles could bind the consciences of men in Christian doctrine absolutely, of which there is no dispute, then early Christians couldn’t freely reject apostolic teaching without sin. Since the Church was given the power of binding of loosing, Christians today cannot appeal to their private judgments to overturn dogmatic pronouncements.
(5) Perspicuity is Refuted by Scripture
Underlying the doctrine of sola scriptura is the perspicuity (or clarity) of Scripture. The perspicuity of scripture holds that the central Christian doctrines pertaining to salvation are so explicitly taught in Scripture that even the unlearned can ascertain them. Although not a strict refutation of perspicuity, we can undermine this doctrine on a practical level by highlighting the divisions among protestant sects on even the most basic Christian doctrines such as justification (Calvinism vs. Arminianism) and the sacraments (e.g., baptismal regeneration and the Eucharist). A misinformed understanding of the sacraments will undoubtedly influence ecclesial practice concerning the administration of the sacraments (e.g., infant baptism).This practical division highlights the need for an external authority to clarify the meaning of Scripture. This is clearly indicated in the story of Phillip and the Ethiopian Eunuch. “So Philip ran to him and heard him reading Isaiah the prophet and asked, “Do you understand what you are reading?” And he said, “How can I, unless someone guides me?” And he invited Philip to come up and sit with him” (Acts 8:30-31).
St. Peter also implicitly undermines the doctrine of perspicuity in his second letter. He writes, "So also our beloved brother Paul wrote to you according to the wisdom given him, speaking of this as he does in all his letters. There are some things in them hard to understand, which the ignorant and unstable twist to their own destruction, as they do the other scriptures" (2 Peter 3:15-16). St. Peter doesn’t clarify which teachings of St. Paul are difficult to understand, but there is no reason to assume that they don’t pertain to doctrines pertaining to salvation.
