The internal evidence for Mosaic authorship of Deuteronomy is in fact, strong, so if you ask my real opinion, the main issue at hand in regards to the question of Mosaic authorship has more to do with faith than evidence or logic. Since the Scriptures are the infallible Word of God, the narrative histories as presented therein are genuine, priceless, and true, as are the various assertions. The original name in Hebrew for this book meant "These are the words..." taken from the first verse of it which says "These are the words which Moses spoke to all Israel across the Jordan in the wilderness..." And that preface sentence introduces the whole book? I don't know how unbelievers and liberal theologians find their way around that except for the fact that their foolish hearts are darkened and the scholars have engaged in a strange level of skepticism, rationalism, and prideful conjecture that undermines what should be the primary aims of their field. Nonetheless the documentary hypothesis, one of the main fallback notions for those who reject Mosaic authorship, can be easily disproven and disregarded for the fact that it rests on and finds its impetus from a series of false premises.
Generally, the documentary hypothesis was a theory to explain authorship of the pentateuch (the first five books of the Bible). This approach to Scripture dates back to the Age of Reason. These "scholars" argued in favor of at least four different sources for the pentateuch. In this hypothesis, Deuteronomy itself is conjectured as a different "source" from the four other Mosaic books and they thought it was from hundreds of years after the death of Moses. They simply think it was written at the time of the reform of king Josiah in 2 Kings 22. I beg to differ. While the text of 2 Kings indicates that Josiah's staff found the lost and forgotten book of the Law (the Old Testament up to that point), there is no indication that Josiah or his people wrote, rewrote, or revised any of the Scriptures. While I am arguing for Mosaic authorship of Deuteronomy in particular, I seek to dismantle this entire documentary hypothesis approach which deals with all five books of the pentateuch. If the hypothesis as a whole is undermined, the the approach to Deuteronomy that it provides is undermined as well, due to the fact that it depends on several essential premises and presuppositions to make it seem right. According to Oswald T. Allis, there were four main areas considered by these critics when supporting the documentary hypothesis: 1) the variations in the divine names in Genesis 2) the secondary variations in diction and style 3) the parallel or duplicate accounts 4) the continuity of the various sources (from Allis, Oswald T. The Five Books of Moses. Phillipsburg, New Jersey: Presbyterian and Reformed Publishing Co., 1949. p. 22.) My readers might also want to check out several respectable sources on the documentary hypothesis, such as:
http://carm.org/documentary-hypothesis#footnote1_ce4nxrn and http://www.theopedia.com/jedp-theory
Let me begin to discuss here several of the main problems with the documentary hypothesis.
1) HEBREW WRITING AT THE TIME OF MOSES
Those in favor of the documentary hypothesis support it in part from the premise that they think there was no writing at the time of Moses (or let's face it- they're so lacking in faith that they may think Moses never lived even). There's abundant evidence from archaeology that written alphabets existed before the time of Moses indeed. Some examples are:
1- The Code of Hammurabi- from the period of 2000-1700 B.C.
2- a Ras Shamra tablet showing Ugartic alphabet is the same as modern Hebrew
3-water pitcher from city of Lachish from about 1600 B.C.
For the scholarship and references on these three artifacts, see this article on the same subject- https://apologeticspress.org/apcontent.aspx?category=13&article=36
2) VARYING NAMES OF GOD DOESN'T MEAN DIFFERENT WRITERS
The use of different names for God in the Pentateuch does not lead to, of logical necessity, the conclusion that there must have been a group of different writers or sources. The proponents of the documentary hypothesis use the different names of God present in the writing as the main premise for finding the conclusion that there were different writers or documents. Moses easily could have known these different names of God. He, after all, visited with the Lord face to face as a man speaks with his friend (Exodus 33:11). The different Hebrew names of God used in Deuteronomy have a different meaning, emphasis and import as to God's attributes, but the explanation of this is best explained in the Jewish writings. The use of the different names does not of logical necessity indicate different writers or documents, when it could also be a literary tool to emphasize different attributes and qualities of God. What is more likely the case of the matter is that Moses knew the different names Elohim and Yahweh and used them expressively in the speeches and writing in the five books of the pentateuch. http://www.hebrew4christians.com/Names_of_G-d/Elohim/elohim.html
3) APPEAL TO AGE (BACKWARDS) FALLACY
Implied in the arguments of those who don't support Mosaic authorship of Deuteronomy in any capacity, whether it be the supplementary approach, the documentary hypothesis, or otherwise, is a logical fallacy of a backwards appeal to age. The fallacy of appeal to age is supposed to be, generally, assertions that previous generations had superior wisdom to modern man, and thus conclusions that rely on this wisdom are seen as more true. One cannot say if previous generations had better wisdom, knowledge, or information or not until it is tested and proven logically. To say that they did or didn't as an unproven premise is vapid intellectually. I can visit my local hoe-down and give them a six-pence to receive that level of thinking and information. Proponents of the documentary hypothesis and other late authorship theories seem to rely on the basic idea that understanding of the things of God developed and accumulated slowly over time. Their approach to the names of God indicates this intellectual bias. While it is true the Scriptures exhibit a foundational principle of progressive revelation, the first five books of the Bible are rich and deep with the basics of theology. It is not understood all that Moses knew, because only the canonical writings seem to have survived (most other writings can be debunked, such as the Zohar which is considered pseudepigrapha and not trustworthy). The reasoning here is somewhat circular because I am depending on the historical narratives of Scripture for the fact that Moses lived. The question at hand is in regards to authorship, though. A lot of the respected scholarship takes for granted that Moses lived, but those scholars merely seek to answer in their research and writing whether the historical figure Moses wrote Deuteronomy. They're committing a similar mistake, though, by reasoning in a circle, pre-assuming Moses' existence (it's highly implied in their work, typically, I think).
It is better to keep things simple and just say that Mosaic authorship of Deuteronomy cannot be debunked from a backwards appeal to age. The book is well attested to in ancient manuscript documentation. It is part of one of the most excellent preserved histories of ancient Israel- which is the Old Testament.
The idea that the book seems too ancient to have been preserved and transmitted across generations very well is similarly fallacious. One cannot assume that it was not preserved just because it is an ancient text. It does not follow of logical necessity that it is impossible that the original text has been preserved and transmitted accurately just because it is an ancient text purportedly from the time of Moses. One possibility is that the original text has been preserved perfectly, and that is the viewpoint I adhere to. [An understanding of cold hard propositional logic is necessary to understand what I'm saying here. I am not employing mathematical probability or historical understanding, just propositional logic].
4) THE RATIONALISM AND LIBERAL SCHOLARSHIP INVOLVED ARE THEMSELVES MERELY A PHILOSOPHY
Generally, the documentary hypothesis is outdated pseudo-scholarship with deep philosophical biases from doubt, atheism, secularism, and unbelief. From such a starting point as that, there is no way for scholars to trust the authority of the Scriptures, as well as the inerrancy and infallibility of the Scriptures. To apply literary criticism and textual criticism to try to reconstruct the writing of the pentateuch would obviously result in an intellectual travesty and the scandalous of undermining of the faith of many. Simply taking a historian's approach to the document "Deuteronomy," I do not think there really is a problem with treating it as generally what it appears to be (by and large the words of Moses to his people). See my previous blog post about extra-biblical evidence for the link to the "truthbomb apologetics" article on how historians examine ancient documents. http://thereformerblog.blogspot.com/2016/03/extra-biblical-evidence-for-historical.html Even though this article is primarily about New Testament scholarship, the same problems exist in terms of a great need to bridge people's thinking across disciplines in order to see that there are perhaps other valid scholarly approaches to Scripture besides those approaches maintained by unbelieving scholars and believed by their deceived followers. The documentary hypothesis was supposed to be just that- a hypothesis, not a fully proven theory. The unbelieving atheistic philosophy of the original scholars shaded and darkened their approach to the Scriptures a great deal.Their approach, their intellectual tools, and their hypothesis is a worldly philosophy, and shouldn't be a considered a respected academic research. Since the hypothesis is old and kind of outmoded, it is fun for me to "pick on," but I don't think there will be many proponents of it who will be very concerned. There a variety of other theories and models that they rely on. I might touch upon a few of these others in a future blog post here.
5) PARALLEL/DUPLICATE ACCOUNTS ARE NOT NECESSARILY EVIDENCE FOR DIFFERENT SOURCES
The name Deuteronomy means "the second law" and is derived from the language of the Septuagint- an ancient version of the Old Testament in Greek (Latinized form of the LXX title). This is a misnomer, however, because the book is simply the words of Moses giving the same law again to a second generation- those who had not died in the plague in the wilderness on the journey to the promised land (Deuteronomy 4:3 and Numbers 25). Twenty-four thousand people died in the plague mentioned in Numbers 25. The words of Moses in Deuteronomy were originally intended for the remaining people- the next generation, ostensibly, who found themselves old enough at that point to receive Moses's reiteration of God's law. The different and new audience could definitely explain the differences in style and voice from the previous books. Moses's love and care for them, that they receive and understand what God expected was outstanding and excellent. Since Moses was reiterating Israel's history and God's law, promises, and covenant to a people group whose membership had significantly changed (though a lot of them were there before, just young), we can expect a change in style and voice which is well-put and tailored to that group receiving and understanding. Add in to the equation the fact that by that point Moses had a greater amount of leadership experience compared to the time of the Exodus.
The book of Deuteronomy details the giving of the law again to a next generation of Israelites who had survived the plague. It is repetitive with previous material for that reason. To miss that point in scholarly endeavors is really asinine. When scholars postulate such theories as the documentary hypothesis, what they actually seem to cover over and hide is God's love, care, and concern, and Moses's care and concern for his people in making sure they understood God's law and what would be expected when they finally took the promised land.
If repetitive passages at the micro-level are the concern, it is known that Deuteronomy contains chiastic structures which are simply a literary device. There is no evidence to say that Moses couldn't have known how to use chiasms by the end of his life. There is evidence to say he did in fact know about them, because chiasms are used in the book of Genesis even.
I support the viewpoint that Deuteronomy is largely the work of Moses himself, but there could easily have been a redactor or secretary involved in penning the autograph. I tend to think that second person was a contemporary of Moses's. The intro in 1:1-5 and the account of Moses's death could easily have been written by such a person.This viewpoint fits into what scholars call a "supplementary" approach or hypothesis, and would actually be very acceptable academically, I think.
