My point to Lampo is that the canon of scripture was not infallibly defined (for Catholics) until Trent.
That’s not true, JonNC. The charism of infallibility is in place when all the bishops, in union with the pope, make a declaration. This is precisely the case when the councils or Rome, Hippo and Carthage decided the canon of scripture in the late 4th Century.
“The order of the Old Testament begins here: Genesis, one book; Exodus, one book; Leviticus, one book; Numbers, one book; Deuteronomy, one book; Joshua [Son of] Nave, one book; Judges, one book; Ruth, one book; Kings, four books [ie., 1 and 2 Samuel and 1 and 2 Kings]; Paralipomenon [Chronicles], two books; Psalms, one book; Solomon, three books: Proverbs, one book; Ecclesiastes, one book; Canticle of Canticles, one book; likewise Wisdom, one book; Ecclesiasticus [Sirach], one book. Likewise the order of the Prophets. Isaias one book, Jeremias one book,…lamentations, Ezechiel one book, Daniel one book, Osee … Nahum … Habacuc … Sophonias … Aggeus … Zacharias … Malachias … Likewise the order of the historical [books]: Job, one book; Tobit, one book; Esdras, two books [Ezra and Nehemiah]; Esther, one book; Judith, one book; Maccabees, two books.” Council of Rome, Decree of Pope Damasus (A.D. 382).
“That nothing be read in church besides the Canonical Scripture. Item, that besides the Canonical Scriptures nothing be read in church under the name of divine Scripture. But the Canonical Scriptures are as follows: Genesis. Exodus. Leviticus. Numbers. Deuteronomy. Joshua the Son of Nun. The Judges. Ruth. The Kings, four books. The Chronicles, two books. Job. The Psalter. The Five books of Solomon. The Twelve Books of the Prophets. Isaiah. Jeremiah. Ezechiel. Daniel. Tobit. Judith. Esther. Ezra, two books. Macchabees, two books.” Council of Hippo, Canon 36 (A.D. 393).
“[It has been decided] that nothing except the canonical Scriptures should be read in the Church under the name of the divine Scriptures. But the canonical Scriptures are: Genesis, Exodus, Leviticus, Numbers, Deuteronomy, Joshua, Judges, Ruth, four books of Kings, Paralipomenon, two books, Job, the Psalter of David, five books of Solomon [Proverbs, Ecclesiastes, Song of Songs, Wisdom, Sirach], twelve books of the Prophets, Isaiah, Jeremiah, Daniel, Ezekiel, Tobit, Judith, Esther, two books of Esdras, two books of the Maccabees.” Council of Carthage III, Canon 397 (A.D. 397).
Protestants must argue that the canon of Scripture is fallible because they know that the Catholic Church determined the canon of Scripture at councils in A.D. 382, 393 and 397. If they admit that the Catholic Church made an infallible decision concerning the canon (which is true), then they would have to explain why they don’t follow the Catholic Church’s other infallible teachings. To skirt the issue, they must argue that the canon is only a fallible collection of infallible books.
If the canon were only a fallible collection of infallible books, then why should we believe that the books in the canon are themselves infallible? The infallible books do not tell us what the canon should be, and this forces us to look outside the infallible books to understand how the canon was selected. This outside source was the Holy Catholic Church, who made the infallible decision concerning what Scriptures were inspired and canonical, and what Scriptures were not.
Moreover, if the canon is only a fallible collection, then this means other books could be added to the canon, and books currently in the canon could be removed. This means that, if the canon of Scripture is infallible, its determination had to come from an infallible source as well. Arguing for a fallible canon also means that Protestants have no basis to deny the canonicity of other religious writings such as the book of Mormon, etc. They have no authority to do so.