I recently encountered an exchange between an LDS apologist and a Protestant on twitter. I tend to avoid such debates, due to the character limit (150 characters is not enough to engage in a meaningful discussion of any topic), but the Protestant apologist ("blainebowden") raised two rather weak arguments in favour of sola scriptura:
One simple thing I don't understand is . . . If you believe the bible, why do you need the Book of Mormon? Isn't Gen-Rev enough?
Unless one will argue that the warning in Rev 22:18-19 is “proof” of sola and tota scriptura, was understood by Protestantism (which it is not), this is question-begging to the highest degree. This may be enough for some, but for those who privilege sound exegesis, sola scriptura is clearly found wanting on this score (search "sola scriptura" on this blog to see the main texts exegeted in careful detail--it is a man-made, anti-biblical tradition).
Once Christ ascended and the Word was sent to the Gentiles, it's finished. There's no need for more until the second coming.
If that was the case, all the New Testament would discuss would be events up to and including the ascension of Jesus in Acts 1:11. However, events post-dating the ascension are discussed (Acts 1:12 onwards . . . ) and the Pauline epistles and other texts not only detail issues post-dating the ascension, they were also written after the ascension. So, obviously, Gen-Rev is too much for this one misinformed Protestant apologist. The Protestant canon of 66 books could not be in view in such comments as the "Word" (being defined here as the Scripture given up to the point the Gospel was preached to all nations) was not completed (indeed, the record of the ascension in Acts 1;11 was not record, so perhaps, if one were consistent, the entire New Testament should be thrown out; after all, it was written after the gospel was preached to the Jews and the Gentiles! Of course, I am being flippant, but that is the inane and illogical hermeneutic bred by this false tradition).
Again, the words of Robert Sungenis hold true on the impossibility of proving sola scriptura from the Bible:
Evangelical James White admits: “Protestants do not assert that Sola Scriptura is a valid concept during times of revelation. How could it be, since the rule of faith to which it points was at the very time coming into being?” (“A Review and Rebuttal of Steve Ray's Article Why the Bereans Rejected Sola Scriptura,” 1997, on web site of Alpha and Omega Ministries). By this admission, White has unwittingly proven that Scripture does not teach Sola Scriptura, for if it cannot be a “valid concept during times of revelation,” how can Scripture teach such a doctrine since Scripture was written precisely when divine oral revelation was being produced? Scripture cannot contradict itself. Since both the 1st century Christian and the 21st century Christian cannot extract differing interpretations from the same verse, thus, whatever was true about Scripture then also be true today. If the first Christians did not, and could not extract sola scriptura from Scripture because oral revelation was still existent, then obviously those verses could not, in principle, be teaching Sola Scriptura, and thus we cannot interpret them as teaching it either. (“Does Scripture teach Sola Scriptura?” in Robert A. Sungenis, ed. Not by Scripture Alone: A Catholic Critique of the Protestant Doctrine of Sola Scriptura [San Goleta, Calif.: Queenship Publishing, 1997], pp. 106-67, here, p. 128 n. 24).
