Thesis 1: The composition of the canon of scripture (what books belong in the Bible) cannot be determined by recourse to scripture both because of the circular nature of the argument and (even ignoring the circularity) because none of the proposed canons address the issue of canonicity in sufficient detail.
Thesis 2: The composition of the canon cannot reliably be determined by recourse to an “inner witness” because of its radical subjectivity. (Even the LDS church claims an “inner witness” for its canon, as do many Protestants for their canon, etc.)
Thesis 3: The question of the canon can therefore only be answered by recourse to the authority of the Church as expressed in magisterial rulings and patristic sources.
Thesis 4: The Protestant canon was not supported by any Church council or ecclesiastical ruling prior to the Reformation. (I’m 99% sure of this, but if I’m mistaken, please correct me.)
Thesis 5: The Protestant canon can only claim one Church Father (Jerome) as support, but even that isn’t unambiguous, as his Latin translation of the Bible does include the deuterocanonicals.