This debate that was supposed to be a debate about indulgences turned into a debate about Church Authority and Protestant canon. Peter lives in the modern time where epistemology is done without any regard for metaphysics, but that hasn’t been the narrative throughout history. Williams only challenges to White in this debate was about his way of coming to a knowledge of the canon. James White gave a near externalist account of it where canon causes a positive doxastic attitude towards a proposition. The debate almost reminds you of the problem of the criterion. Do you start with particular examples of knowledge? Or do you start with a method to distinguish knowledge from belief? The debate shows the real debate over the centuries has always been Church Authority.

http://spirited-tech.com/COG/2017/06/07/the-issue-of-canon-and-sola-scriptura/