I have recently read Michael Heiser’s interactions with John Hobbins ‘thoughts about canon’ posts here, here and here. I have found this discussion very interesting and helpful. The topic of the canon, especially the canon of the OT has interested me for some time, and I might even say, troubled me for some time. This question is intrinsically linked to the problem of inerrancy, which I have discussed earlier

There are several problems with the concept of canon, as it is narrowly defined. The first is the problem that different churches accept different canons. The famous example being the inclusion of much of the ‘so called’ apocrypha by the Orthodox and Catholic churches, and the rejection of those books by Protestant churches. But the other problem, in my mind, is the Septuagint, which is still recognized as the Old Testament by Orthodox churches today, though both Protestant and Catholic churches have accepted the Hebrew Masoretic Text.  The Septuagint represents a different list of cannon, including such books as Maccabees, 1 Esdras, Judith, Tobit, Wisdom of Solomon, Sirach, Baruch and new parts of Daniel. 

The major difficulty that the Septuagint poses is the fact that it seems that it was the accepted canon of the earliest church. It stayed accepted until Jerome’s Latin Vulgate, which was based on the MT much to Augustine’s chagrin, won the day as the accepted Scripture of the church. So the earliest church accepted the LXX but the later church accepted the MT, we have some discontinuity in our church history. I have no clear solution to this problem, but having just finished Martin Hengel’s excellent book, The Septuagint as Christian Scripture, I’ll just offer this quote as something to think about:

Does the church still need a clearly demarcated, strictly closed Old Testament canon, since the New Testament is, after all, the ‘conclusion’, the goal and the fulfillment of the Old? (M. Hengel, The Septuagint as Christian Scripture [Grand Rapids, BakerAcademic, 2002], 125-26).