Today’s adventure in biblical interpretation is Leviticus 18:17-18. This was brought to my attention in a comment by Artisianal Toad, a proponent of polygyny. While you can read the comment quoted below, you can also read his full rationale on his blog.
“Oh, did you notice that not only is there no prohibition of female homosexuality in the Law, but the incest statutes that apply to polygyny (Leviticus 18:17-18) presume sexual contact between wives in such a marriage?”
There is a lot packed into this short statement. It is saying that polygyny is acceptable, that female genital contact is accepted in a polygynist relationship, and that there is nothing wrong with female homosexuality in general. While a lot could be written on these three topics, I’m only going to address the notion that this passage of Bible is about incest and that it presumes that wives in a plural-marriage will be making genital contact with each other.
Leviticus 18 is a passage that condemns various sexual practices. Most of the practices forbidden are incest, but there are a few others cases (such as sex with an animal) that are also forbidden. Verses 17 and 18 read:
“17You are not to uncover the nakedness of a woman and her daughter. You are not to take her son’s daughter, or her daughter’s daughter, to uncover her nakedness; they are near kinswomen. It is wickedness. 18You are not to take a wife to her sister, to be a rival, to uncover her nakedness while her sister is yet alive.” (REV)
Let’s start with verse 18. A man is not to marry two sisters because this would most likely cause significant rivalry. The case of Jacob and his wives, sisters Leah and Rachel, is a classic illustration of this and possibly the reason behind this regulation. While this is an interesting regulation as it pertains to polygyny, there is no indication in this verse that marrying sisters would necessarily result in genital contact among sisters.
One argument is that this command (v18) comes immediately after the other instances of incest (v6-17), so it is inferred that this must also be incest. However, the following verse (v19) is certainly not about incest. There is no reason to infer from the placement of v18 that it is describing incest when it explicitly gives the reason for the command as rivalry, not incest. If it is not incest, then genital contact cannot be inferred.
The other argument requires quoting the verse from the KJV:
“Neither shalt thou take a wife to her sister, to vex her, to uncover her nakedness, beside the other in her life time.”
The interpretation goes something like this: “don’t marry the sister of your wife for it would upset her if you had sex with her sister beside her.” “Beside the other” is taken to literally mean that the two women are beside each other while the man is having sex. But that is obviously not the correct meaning. It makes no sense to say that they should not have threesome sex during her lifetime, as if it would be fine to have all three having sex in bed as long as one of them were dead. This very strange interpretation is only due to the way the text is translated in the KJV. It is not supported by other translations or commentaries.
So we must back up to verse 17 and see if that supports the original claim. It explicitly forbids marrying your wife’s daughter or her granddaughter. (It also applies in reverse: to marrying the mother or grandmother of your wife.)
The argument is that because it says “and” that it is implying that the wife and daughter are married at the same time and that this is incest because the women are having sexual genital contact with each other. But the text does not say this. Incest is not defined as genital contact between two women, it is defined as a man marrying a blood-relative or near-relative (v6). Verse 17 just continues the prohibitions against marrying an in-law (v12-16). The prohibition against marrying your wife’s daughter or granddaughter or any in-law or any blood-relative applies even if your wife dies.
The original premise does not hold up to scrutiny. Verse 17 isn’t even about polygyny, so it can’t be used to to make any statement at all regarding genital contact between women. Only verse 18 has anything to do with polygyny, yet it still has nothing to do with genital contact.
In a previous adventure, I showed how some biblical interpretations take after the biases of those performing the interpretations, even if the face of absurdities. In this adventure, it is plain that the suggested interpretation suffers from a significant amount of reading a conclusion into the text, or eisegesis. This yields itself to weak arguments that don’t hold up to scrutiny. While it obviously isn’t impossible for a non-traditional interpretation to be correct, the proposed alternative better have a rock solid argument to back it up.
 See the Adam Clark Commentary section on Leviticus 18:18.
 As this is a particularly evocative statement, let’s break it down logically. If the vexing is seeing her sister have sex with her own husband, then why even mention her lifetime? There is no need for a lifetime ban on the marriage if that was the source of vexation. Why not just command that the wives have separate bedrooms? Or you could allow the marriage of two sisters if they agreed that threesome sex was not vexing. If the concern was that the threesome would be uncomfortable, the lifetime of the participants would not be the logical solution to the problem.
 See John Gill’s Exposition of the Whole Bible section on Leviticus 18:17-18.
 “Beside the other – Law against polygamy” in Expanded Biblical Comments – Commentary of the Old and New Testament. Charles Taze Russell, 1916
 “Leviticus 18:18 is quite clearly a ban on a particular type of polygamy, in the context of law-order which permitted polygamy in general…If a man has a barren wife, he is not to seek a woman capable of having children among his wife’s kin.” in Man and Woman in Biblical Law. Tom Shipley, 2010. p.128.
 According to his own argument that the Bible does not treat genital contact by women as sex. Therefore, it can’t be incest.
 That is, having sex with.
 Notice also what I don’t say. My response does not preclude the possibility of approved genital contact between women, it only rejects Leviticus 18 as support of that possibility. There may be other evidence for or against that premise, but it can’t be found here. My conclusion is restricted to the narrowly argued case that I presented.
 This argument was made at http://www.christianpoly.org/lev18.php