I thought it was fascinating that Whitaker did not first treat of the authority of Scripture in his book. Instead, he argues about the canon. There is a very good reason for this particular order. And that is that one cannot really speak about the authority of the canon unless the canon is defined first. Which books have (potentially in the argument) authority and which do not?
Whitaker starts off defining canon this way: “The books of scripture are called canonical, because they contain the standard and rule of our faith and morals. For the scripture is in the church what the law is in a state.” (emphasis original, p. 27). The canon is the rule of faith and practice. He quotes Augustine (I will be seeking to track down patristic quotations and give them in both translation and original whenever possible, though I will not be exhaustive in this: only what I deem the more important quotations will I track down), saying “whatever belongs to faith and moral life may be found in the scriptures” (p. 28). Although it is not mentioned here, the quotation comes from De Doctrina Christiana, which has been translated recently by Edmund Hill in the New City Press version as Teaching Christianity. There, it reads “The fact is, after all, that in the passages that are put plainly in scripture is to be found everything that that touches upon faith, and good morals, that is to say hope and charity, which we dealt with in the previous book.” This is available in the original Latin series Patrologia Latinae on Google books here, and the quotation in Latin is on page 42. Augustine goes on to say (quoting Hill’s version): “instances from the plainer passages are used to cast light on the more obscure utterances, and the testimony of some undoubted judgments is used to remove uncertainties from those that are more doubtful” (ibid.). Here we actually see the sufficiency of Scripture, as well as the perspicuity of Scripture. For Augustine clearly states here that everything that touches upon faith and good morals is found plainly in scripture (of course Augustine does not believe that all passages in scripture are clear: but then, neither do any Protestants of whom I am aware). Further, we see the rule of scripture interpreting scripture here as well, where the more clear scriptures shed light on the less clear. He goes on to note that a good memory is of the greatest value, therefore, in rightly interpreting scripture.
If the fathers are right about the importance of the canon, then the question becomes one of which books are canonical. Here the Romanists and the Protestants differ on the matter of six books in particular: Tobit, Judith, Wisdom, 1 and 2 Maccabees, Sirach (also called Ecclesiasticus). That the Romanists still have this difference with Protestants is clear from the Catechism of the Catholic Church, p. 40 (section IV 120), although there it is clear that Baruch is regarded as canonical as well. According to Whitaker (29), the Jesuits interpreted Trent to include Baruch, the Hymn of the Three Children, Susannah, Bel and the Dragon, and the additions to Esther. However, these are not explicitly mentioned in Trent or the Catechism, except Baruch (see Session IV of the Council of Trent).