Concerning Jeremiah: does the lengthier text tradition found in the MT represent an expansion of the tradition that backed the LXX? Or does the tradition behind the LXX represent an abridgment of the Masoretic Text? Or do the two traditions relate to each other in some other way?
The LXX and MT texts of Jeremiah are substantially different. The LXX is substantially shorter (around an eighth shorter) and the order of some of the text is different. This is much more substantial than most divergences between the LXX and MT.
In general, there are two main ways in which the MT and LXX can differ: the Hebrew text that the LXX translators were translating from was substantially different from the MT or the LXX translators translated loosely. In this case, we can be pretty confident that much of the difference is caused by the former issue. This is because in the Dead Sea Scrolls there are fragments of Hebrew texts of Jeremiah which agree with the LXX and not the MT.
Let's fix terminology and call the Hebrew text of Jeremiah circulating circa 2nd century BCE which was translated into the LXX the "proto-LXX" and the Hebrew text of Jeremiah circulating around the same time which was chosen a millennium later by the Masoretes the "proto-MT." Since the two are so substantially different, it is highly unlikely that the differences were caused simply by scribal errors, instead someone actively editing and rewriting happened at some point. There are three possibilities: the proto-LXX is edited from a proto-MT original, the proto-MT is edited from a proto-LXX original, or both were edited from a lost original. In the absence of a compelling reason for the third option, I'll concentrate on the former two.
Once you know that one of two texts is a redaction (edited version) of the other, you can use redaction criticism which attempts to figure out what the goals, language, and themes of the redactor were. So you can ask "does it make more sense that someone edited proto-LXX to proto-MT in order to do XYZ, or vice-versa?" A standard example of this kind of argument is the argument that it is more likely that Matthew and Luke redacted Mark than vice-versa.
From a quick search it seems that a strong majority of scholars think the proto-LXX is the original and the proto-MT was a revision. A major argument is that the redactor of the proto-MT was shows signs of working several centuries later. Another is that the proto-MT clarifies several confusing sections in the proto-LXX. I have not yet turned up a good snappy summary of the arguments anywhere in the literature yet.
In summary, the differences between the LXX and MT are caused mostly by the differences between the ancient Hebrew proto-LXX and proto-MT texts, not by translations. One of these versions was a revision of the other, and a strong majority of scholars thing that the proto-LXX was the original and that the proto-MT shows evidence of being a revision.
Several modern critical commentaries confidently dismiss in methodological exactness the typical traditional reasons why many have held that the ‘MT is superior to the LXX’. For example on reviewing the omissions of the LXX which represents the largest difference, here is a concise summary of old ideas rejected by a critical commentary:
These (in common with other variations) have been ascribed to carelessness on the part of copyists (St Jerome), or to their ignorance (Hitzig, Umbreit), or to haste in their transcription of the LXX.’s Hebrew original (so Dean Payne Smith in Speaker’s Comm. Introd. to J., Vol. v. pp. 324 f.); or on the other hand to the translators’ design, this last view finding numerous defenders (Naegelsbach, Keil, etc.) (Streane, A. W. The Double Text of Jeremiah (Massoretic and Alexandrian Compared) together with an Appendix on the Old Latin Evidence (pp. 3–4). Cambridge: Deighton Bell and Co.)
The author then proceeds to dismiss each concept and argues that the LXX is actually quite obviously superior to the MT. The basic argument is essentially that there is no evidence to support that the translators of the LXX were careless, ignorant, or hasty, or benefiting with any agenda for the many differences but that they must have been working with a different copy of the Hebrew.
It is clear that such of the sacred Books as depended for their preservation and study upon the devotion or literary interest of individuals only, would be liable to a far larger amount of alteration, intentional and otherwise, than those which, through their use in public worship, secured a larger amount of attention, and consequently, comparatively speaking, more of verbal accuracy in their transmission. (Streane, A. W. The Double Text of Jeremiah (Massoretic and Alexandrian Compared) together with an Appendix on the Old Latin Evidence (p. 8). Cambridge: Deighton Bell and Co.)
So basically the argument in favor of the LXX in very simple form is: ‘I trust manuscripts that were more public and trust the persons who made the translations as they seemed honest and intelligent.’ Of course the actual argument is made using detailed arguments about each differing case, but all biased under this basic approach.
For me I take the opposite opinion. First, regardless of which manuscripts were used by the public and regardless of how intelligent and honest the LXX translators may have been, one should always give more credence to an original copy then to a translated copy all other things being equal. In other words one should start with a bias for the original language (the MT) then only if the evidence is overwhelming that something is wrong with the original -that the copy truly explains- should we even consider the copy as the better authority. I feel those arguing LXX supremacy simply abandon the MT prematurely without cause. (I have not reviewed each detail. I am only arguing from a sampling of the detailed arguments paying more attention to the general argument and assumption).
To me a good example case that puts the MT in a higher position is a very large change in the arrangement of the LXX version. Verse 25:14 is missing in the LXX and in its place the LXX inserts:
the prophecy against Elam (49:34, 39, Heb.) follows directly on ver. 13. Then the others come in the following order: against Egypt (ch. 46), against Babylon (chh. 50. and 51.), against Philistia, Tyrus and Sidon (47:1–7), against Edom (49:7–22), against Ammon (49:1–5), against Kedar (49:28–33), against Damascus (49:23–27), against Moab (ch. 48). Then follows 25:15–38 as a comprehensive conclusion.( Lange, J. P., Schaff, P., Nägelsbach, C. W. E., & Asbury, S. R. (2008). A commentary on the Holy Scriptures: Jeremiah (p. 231)
One has to look into something like this for one’s self, but for me I simply find the internal logic and flow of the MT more meaningful compared to what appears to be a rearrangement in the LXX. The omission and additions are less conclusive and conjectural (something I think the supporters of the LXX seem to base most of their arguments on) than the internal reasonableness and flow of each one. Combining the reasonable bias for an original language to that of a copy plus this reduced quality of logical flow by the LXX significant re-arrangements I think the MT is the better source. Of course these sorts or arguments never end because each person investigating the subject puts energy into proving their initial suspicions at a higher level. Both argue that there favorite source 'has better flow' but I simply do not see it in the LXX.
Regarding the Dead Sea Scrolls most of them seem to have conformed to the MT but there is a 'claim' that some follow the LXX prototype which I am unable to find real significant proof of. Here is a summary of all the related scriptures based on the book, Scanlin, H. P. (1993). The Dead Sea Scrolls & Modern Translations of the Old Testament. Wheaton, IL: Tyndale House Publishers
Here are the scrolls that are supposedly in favor of the MT:
Name: 4QJera Content: Jeremiah 7:29–34; 8:1 (?)–6; 9:1 (?)–2, 7–14; 10:9–14; 11:3–6; 12:3–6, 13–17; 13:1–7; 14:4–7; 15:1–2; 17:8–26; 18:15–23; 19:1; 22:4–16 Bibliography: plates: ER 1159 (43.075), ER 1253 (43.216) +; Janzen (1973), not all columns reported. Tov (1989) reports fifteen columns between 7:1 and 26:10 Date: c. 200 B.C. (Cross); late third or early second century B.C. (Yardeni) Significance: The manuscript generally follows proto-MT.
Name: 4QJerc Content: Jeremiah 4:5, 13–16; 8:1–3, 21–23; 9:1–5; 10:12–13; 19:8–9(?); 20:1–5(?), 7–9(?), –15; 21:7–10; 22:4–6, 10–28; 25:7–8, 15–17, 24–26; 26:10–13; 27:1–3, 13–15; 30:–24; 31:1–14, –26; 33:16–20 Bibliography: plates: ER 1185 (43.101), ER 1187–90 (43.103–6) +; Tov (1991) Date: uncertain Significance: The text is very close to proto-MT.
Name: 2QJer (= 2Q13) Content: Jeremiah 42:7–11, 14; 43:8–11; 44:1–3, 12–14; 46:27–28; 47:1–7; 48:7, 25–39, 43–45; 49:10 Bibliography: DJD 3 Date: Herodian Significance: Although some readings agree with the LXX, the order of the chapters follows the proto-MT.
Here are the scrolls that are supposedly similar to the LXX:
Name: 4QJerb Content: Jeremiah 9:22–26; 10:1–18 Bibliography: plates: ER 154 (41.146), 759 (42.280), 1162 (43.078) +; Tov (1989, 1992d). Yardeni (1990) discusses in detail the orthography of this manuscript. Date: Hasmonean (Cross) Significance: The text resembles LXX arrangement and shortness; the orthography is proto-MT.
Here are the scrolls that have no significance:
Name: 4QJerd (earlier reported as part of 4QJerb) Content: Jeremiah 43:2–10
Name: 4QJere (earlier reported as part of 4QJerb) Content: Jeremiah 50:4–6
So it should seem quite obvious that the only claimed section of scripture that lends itself to the argument of the superiority of the proto-LXX is Jeremiah 9:22–26; 10:1–18
Let’s look at one of these important important sections under the ESV translation (I assume primarily based on the MT) and also on an English translation of the Dead Sea Scrolls, as well as a LXX English translation to see what are people really making these claims at a level of the actual overall meaning that each one is conveying and how divergent they are?
Jeremiah 9:23-26 (The Holy Bible: English Standard Version. (2001)
23 Thus says the LORD: “Let not the wise man boast in his wisdom, let not the mighty man boast in his might, let not the rich man boast in his riches, 24 but let him who boasts boast in this, that he understands and knows me, that I am the LORD who practices steadfast love, justice, and righteousness in the earth. For in these things I delight, declares the LORD.” 25 “Behold, the days are coming, declares the LORD, when I will punish all those who are circumcised merely in the flesh— 26 Egypt, Judah, Edom, the sons of Ammon, Moab, and all who dwell in the desert who cut the corners of their hair, for all these nations are uncircumcised, and all the house of Israel are uncircumcised in heart.”
Jeremiah 9:23-26 (Brannan, R., Penner, K. M., Loken, I., Aubrey, M., & Hoogendyk, I. (Eds.). (2012). The Lexham English Septuagint)
23* This is what the Lord says: “Let the wise not boast in his wisdom, and let the strong not boast in his strength, and let the wealthy not boast in his riches. 24* ⌊Rather⌋ let the one who boasts boast in this: that he understands and knows that I am the Lord, the one who deals in mercy and judgment and righteousness upon the earth. For my will is in this,” says the Lord. 25* “Look! The day is coming,” says the Lord, “and I will visit upon all the circumcised their foreskins, 26* upon Egypt and upon Idumea and upon Edom and upon the descendants of Ammon and upon the descendants of Moab and upon all those who shave around ⌊that which is upon his face⌋, those who dwell in the desert, because every nation is uncircumcised in flesh, and the whole house of Israel is uncircumcised in their heart.”
Jeremiah 9:23-26 Abegg, M., Jr., Flint, P., & Ulrich, E. (1999). The Dead Sea Scrolls Bible: The Oldest Known Bible Translated for the First Time into English (p. 388).
23 [Thus says the LORD: Do not let the wise person boast in] his wisd[om], nor let [the strong man boa]st [in his might, do not the rich glory in his riches; 24 but let the one who boasts boast in this: that he understands and knows me, that I am the LORD who exercises lovingkindness, justi]ce, and righteousness in the earth—for [in these things I delight, says the LORD. 25 See, the days are coming, says the LORD, when I will punish all those who are circumcised only in their foreskin: 26 Egypt, Judah, Edom, the Ammonites, Moab, and all those] with shaven temples who liv[e in the desert. For all these nations are uncircumcised, and all the house of Israel is uncircumcised in heart].
OK I don’t know about you but whatever ‘professor’ decided to send a relay message to those discussing the LXX that this brings evidence to the LXX prototype must know something I can’t see. To me this section does not even indicate any difference to all three versions. The more I hear of these types of arguments and claims the more critical I am at trusting what anyone says until some precise proof is presented. Basically I still think the best and most easily understood proof is that the MT flows more meaningful then does the LXX, or its supposed prototype. I see no evidence to support that before the MT editors were mixing everything up and down and only after the MT was established did they take such great care is preserving the original text. (There might be evidence somewhere but nothing I am able to find, even with fairly good resources at hand). After all, those who try and imagine great revisions occurring before the MT was established are really presupposing intentional revisions during times that no proof is available one way or the other indicating that it is a preferential presupposition that seems to simply be based on ‘distrust’ that the Hebrews actually faithfully recorded the scriptures.
Note: I should mention I am not an expert my any means on this subject. I am just the kind of person who does not trust anyone until I see it for myself. I like to research things for myself based on my skeptical view of human nature. All I can see is that the MT seems more reliable.
The DSS MSS have Hebrew rescentions of both the MT and LXX texts of Jeremiah, so there is really no solution to this problem when refering to them. Both types of texts are present there, so again it is only theory and opinion that gives preference to the text as found in the LXX over that of the MT. The DSS do prove that this issue goes back to a rescention of the Hebrew text, but beyond that, the question of which variant came first must be determined by other factors.