The Prohibition of Marrying Sisters

  • Rav Elchanan Samet

Parshat HaShavua
Yeshivat Har Etzion


The Prohibition of Marrying Sisters

By Rav Elchanan Samet



"You shall not take a woman as a wife after marrying her sister, as her rival, to uncover her nakedness beside the other during her lifetime." (Vayikra 18:18)

The prohibition against marrying sisters is among the long list of forbidden relations included in Vayikra chapter 18. Rambam explains: "Once a person has married a woman, her near relations are forbidden to him" (Hil. Issurei Bi'a 2:7). This prohibition of her near relations is addressed in verses 17-18. Verse 17 prohibits "a woman and her daughter," as well as a woman and her granddaughter (born either of her son or her daughter), while verse 18 adds the prohibition of her sister.

Two expressions in verse 18 require clarification.

a. "As her rival" (litzror) - Rashi comments, "This term is derived from the word 'tzara' (distress) - that each (sister) will cause distress to the other." Rashbam elucidates Rashi's interpretation as follows: "'As her rival' - as in (Shemuel I 1:6), 'And her rival provoked her.' [In a polygamous society,] two women married [at the same time] to the same man are called a distress to each other."

This idea requires further explanation. The prohibition applies not only to a person who marries two sisters, making them into permanent rivals - for after he marries one sister, the other is forbidden to him, and any "marriage" to the second does not take effect. The verse furthermore prohibits any relations with his wife's sister - even a one-time affair, as stated in the conclusion, "to uncover her nakedness beside the other (his wife)." But the reason for the prohibition is, as Ramban teaches, "For it is not proper that one take a woman and her sister (as wives), making them into rivals, for they should love one another and not distress each other."

b. "During her lifetime" - while the relatives of the wife mentioned in verse 17 are "each forbidden to him forever, whether he divorces her, or she is still alive, or after her death," a woman's sister is "forbidden to him until his wife dies" (Rambam, ibid.). After his wife's death, her sister is completely permissible to him, and such marriages have been quite commonplace throughout the generations.

While the expression "during her lifetime" makes the marriage permissible after his wife's death, it also involves a limitation: even if the man and his wife are divorced, her sister remains forbidden to him so long as the divorced wife is still alive. This requires emphasis, especially in light of the reason given for the prohibition: "as a rival."

The prohibition of marrying the sister of one's wife is the only one among all the forbidden relations which, although arising from a blood relationship, is nullified upon the death of the person who represented the reason for it. Although there are two other "temporary" forbidden relations - "nidda," a menstruant woman, which is nullified after the woman's immersion in a mikveh, and a married woman, who becomes permissible if she is either divorced or widowed - neither of these arises from a blood relationship.

This unique characteristic of the prohibition against marrying one's wife's sister explains its position - at the end of the list of forbidden relationships arising from family ties, and prior to the prohibitions against a "nidda" and a married woman (verses 19-20). Since it belongs partially to both groups, it is located in between them.

Why is the prohibition against marrying the sister more lenient than the prohibition against the wife's other relatives (mentioned in verse 17) or the women married to the husband's relatives? Why is the sister the only woman who becomes permissible after the death of the person because of whom she was forbidden? This question leads us to a discussion of the reason and definition of the prohibition against marrying one's wife's sister. It is clear that there is some connection between the two expressions addressed above - "as her rival" and "during her lifetime," and this connection is the key to answering the question. We shall return to this subject later on.


The prohibition of "You shall not take a woman as a wife after marrying her sister" immediately raises a question: Yaakov, our forefather, married two sisters - "Rachel and Leah, who jointly built the House of Israel" (Ruth 4:11). How could Yaakov have transgressed one of the prohibitions of forbidden relationships listed in our parasha?

At first glance, the question does not seem too difficult. Rav David Zvi Hoffmann concludes his commentary on our verse as follows: "The prohibition against marrying two sisters did not exist prior to the giving of the Torah at Sinai, as proved by Yaakov's actions."

The Ramban (Bereishit 26:5) nevertheless has a problem with Yaakov's marriage to two sisters, for he seeks to reconcile this situation with the midrash of Chazal according to which the forefathers observed the entire Torah even prior to Sinai. But if we do not regard this midrash as reflecting the literal text, then the question never arises.

But it's not as simple as that. Even a "literal" commentator like Ibn Ezra grapples with this question in his commentary on our verse, with no reference whatsoever to the midrash of Chazal. Although he does not explicitly formulate his difficulty, we can deduce it from his answer. The forbidden relations in our chapter are set out within a rhetorical framework that describes them as "abominations" through which the Canaanite nations were defiled, and as a result of which the land became polluted and vomited out its inhabitants. This being the case, the nature of these actions is not related to or dependent on the giving of the Torah; they obligate - and have always obligated - even the nations of the world. Thus, we return to our question: how could Yaakov transgress one of the "abominable" prohibitions that characterize the worst of the nations?

Ibn Ezra answers as follows:

"Mistaken is the one who explains that Rachel and Leah were not sisters, proving this with the words, 'for all of these abominations….' This is not a sound proof… Others have claimed that although the Torah says, 'all of these abominations…,' as a general description, it does not thereby refer to all of them (the forbidden relations), but rather only to most of them."

What Ibn Ezra means is that the prohibition against marrying two sisters does not fall into the category of "abomination," and it was not because of this prohibition that the nations dwelling in the land were thrown out. Therefore, Yaakov's action is not problematic, for the prohibition against marrying sisters became applicable for Israel only after the giving of the Torah.

If so, in what way is the prohibition against marrying sisters different from the rest of the forbidden relationships, such that it is not defined as an "abomination"? The Karaites noted some unique features of our verse, but explained it incorrectly and against the Halakha. In his listing of the mitzvot, Daniel Al-Qumsi (9th century Persia and Jerusalem) points out that the Torah does not define marriage to two sisters as "foulness" (zima) and "abomination" (to'eva), as it does in the prohibition of the previous verse. This point is worthy of emphasis, for all the forbidden relations in the second half of our chapter (17-23) - those not involving blood relations of the man concerned - give emphasis, in their reasoning, to the sexual vulgarity and ugliness of the deed:

Verse 17: a woman and her daughter, or a woman and her granddaughter - "they are her blood relations; IT IS FOULNESS." "Foulness" in this context denotes licentiousness.

Verse 19: Concerning a woman who is "nidda," the Torah stresses that she is "in the nidda state of HER IMPURITY" - and this explains the prohibition of relations with her.

Verse 20: "You shall not lie agive seed to the wife of yo, TO BECOME IMPURE THROUGH HER."

Verse 22: Homosexuality is "an abomination"

Verse 23: Bestiality is "perversion."

Al-Qumsi also notes that in contrast to the previous verse, in which the blood relationship between the woman and her relatives was stressed ("she is her blood relation"), such emphasis is absent from our verse.

In his "Eshkol Ha-kofer," Yehuda Hadasi (12th century Crimea) likewise notes the unique nature of our verse, and writes as follows:

"The Torah distinguishes this law in two respects: firstly, it does not say, 'You shall not uncover the nakedness of your wife's sister,' as the law is formulated in all the other instances, but rather 'You shall not take a woman as a wife after marrying her sister' … Secondly, concerning all the other forbidden relationships we are told, 'You shall not uncover,' but no reason is given, whereas here, the Torah says 'as her rival, to uncover her nakedness beside the other during her lifetime' - for the rivalry and distress would be only during her (the wife's) lifetime, not after her death."

Hadasi therefore rightly points out that the formulation of our verse is different than that of the preceding prohibitions, and even the prohibition itself is different from the others in that it is based on the rivalry that exists only "during her lifetime," but not after her death.

The Karaites' mistake lay in the conclusion they drew from all of these facts: that our verse is not talking about two sisters (but rather about two wives, or a woman and her niece, or two unequal wives). The proper conclusion is entirely different: that the Torah does not regard marrying two sisters (real, blood sisters) as a perversion or ugliness like marrying a woman and her daughter or a woman and her granddaughter. It is not licentiousness and an abomination, for the family relationship between the women does not make it so.

The forbidden relationships defined as "she'er" in the Torah always pertain to the husband's family relationship with the woman who is forbidden to him (as a result of her status or that of her husband). From this perspective, a woman and her daughter are likewise not "she'er" with regard to the man who is forbidden to marry both of them; "THEY are she'er," the Torah says in their regard, and "they" hints at the woman and her daughter - they are related TO EACH OTHER. And what does this have to do with the man? The answer is that because the one woman was born of the other, maintaining relations with both of them is a kind of licentiousness. But the relationship between two sisters (admittedly born of the same mother, but they themselves are not "one flesh") does not make marrying them an act of licentiousness. (This distinction would seem to be clear from a human, psychological point of view as well.)

Why, then, does the Torah prohibit marrying two sisters? The answer is provided in the text: because it is not MORALLY proper to turn sisters into rivals. This moral reason applies only during the wife's lifetime; after her death there is no reason for the husband not to marry her sister, since this relationship is not defined as "she'er." The deceased wife's sister is not a blood relative of the husband, and her blood relationship with the deceased wife is no longer a valid reason to prohibit the marriage.

The unique formulation of the verse, the absence of any condemnation of the forbidden relationship, the moral reason - "as a rival" - and the special condition - "during her lifetime" - clearly testify to the above conclusion. And this is in fact hinted at in the Ramban's commentary on our verse:

"'As a rival, to uncover her nakedness before the other during her lifetime' - Here the Torah gives the reason for the prohibition; it is not proper that one marry a woman and her sister, turning them into rivals of each other, for they should love one another and not be rivals. The Torah does not say this concerning a woman and her daughter or a woman and her mother, for these are 'she'er,' and (the second relationship is) forbidden even after the woman's death."

Even clearer expression of this idea is to be found in the Seforno:

"'You shall not take… as a rival' - THE TORAH SAYS THAT WERE IT NOT FOR THIS, A WOMAN'S SISTER WOULD NOT BE FORBIDDEN (to her husband as a wife), SINCE SHE IS NOT BORN OF THE WIFE, AND THE SISTER HERSELF IS PERMISSIBLE TO HIM, but the Torah forbids her in order that they will not be rivals. And therefore she forbidden to him only during the wife's lifetime, which is not the case concerning any other of the forbidden relationships."

It is this, then, that Ibn Ezra was hinting at when he points out that the prohibition against the woman's sister is not defined as an "abomination," and therefore Yaakov's act in marring two sisters (prior to the Torah's prohibition of this) need not cause any problem.


Ibn Ezra himself has a different opinion concerning our question. In his commentary on verse 26, "And you shall not perform any of these abominations; neither the Israelite nor the stranger who dwells among you," he asks why a resident non-Jew is likewise committed to refraining from all the prohibited relationships mentioned in our chapter. (This question is similar in nature to his clarification in our verse: were the Canaanites obligated concerning ALL of these forbidden relationships; was it because of all of them that the land ejected them?) He answers as follows:

"This commandment applies equally to an Israelite and to a resident non-Jew BY VIRTUE OF HIS LIVING IN ERETZ YISRAEL (and ALL of these forbidden relationships arise from the special sanctity of the land). And one who has a heart can understand that Yaakov, when he married two sisters IN CHARAN, and also Amram, who married his aunt IN EGYPT (Shemot 6:20), were not thereby defiled."

The connection that Ibn Ezra points out between the entire list of prohibited relationships (as well as other mitzvot, such as idolatry) and living in Eretz Yisrael is addressed at length in his commentary on Devarim 31:16, and is developed and expanded upon in the Ramban's commentary in several places, especially on verse 25 of our chapter.

Ibn Ezra's explanation for Yaakov's marriage to two sisters - that it took place in Charan and not in Eretz Yisrael - is likewise developed and complemented by the Ramban:

"And God alone plans how things work out, that Rachel died on the way, as they began to enter the land. In her merit, she did not die outside Eretz Yisrael, and in his merit, he did not dwell in Eretz Yisrael married to two sisters, for she was married to him in contravention of the prohibition against marrying sisters. It appears that she fell pregnant with Binyamin before they reached Shekhem; Yaakov had no relations with her at all within the land because of the prohibition."

The Ramban is hinting that Yaakov was aware of the fact that the moment he entered the land, the prohibition against two sisters would apply, and therefore "he had no relations with her at all within the land, because of the prohibition." This is expressed more clearly in his commentary on Bereishit 48:7, where he writes: "Yaakov's (true) intention in not taking her (Rachel, after her death) to Me'arat Ha-Makhpela was in order that two sisters would not be buried there, for he would thereby be embarrassed before his fathers."


After all of the above, we have still not received an answer to our question. We have proven that marriage to two sisters is not categorized as a sexual "abomination" (although following the Torah's prohibition, it is punishable - like any other forbidden sexual relations - with "karet," excision). Its reason, as Ramban explains, is that it is not proper to turn two sisters, who should love each other, into rivals. Was Yaakov then blind to this seemingly obvious human reasoning?

Yaakov's original intention was never to marry two sisters. He found himself married to both in the complicated circumstances brought about by Lavan, his father-in-law. In these circumstances - anin the absence of any formal prohibition against marsis- marrying Rachel and allowing Leah to remain in his home was the best and fairest thing that Yaakov could do. Divorcing Leah or refraining from marrying Rachel, in those circumstances, would have been much greater injustices than being married to both - a situation which did, indeed, turn the sisters into rivals in the fullest, most tragic sense.

Although we have shown that Yaakov's marriage to Rachel after marrying Leah is not in any way problematic, we may add a further statement which removes the very question.

The Torah contains various mitzvot that arise from events that happened to our forefathers. Although most date to the time when the nation had already been formed - the Exodus from Egypt and the wanderings in the desert - there are some that are connected to the original forefathers themselves. An example is the prohibition against eating the sinew of the thigh, arising from Yaakov's battle with the angel in parashat Vayishlach (Bereishit 32:25-33).

I propose that the prohibition against marrying sisters likewise should be understood as arising from the events of Yaakov's life. Rachel and Leah, who jointly built the House of Israel, were both worthy of Yaakov, and his act in marrying both was likewise worthy - considering the circumstances and the lack of any prohibition concerning this. But he witnessed the tragic rivalry that developed between them: a hostile rivalry that continued and developed over many years, a rivalry for the love of their husband and a rivalry over bearing children. This difficult relationship is described explicitly in the Torah in chapters 29-30 of Sefer Bereishit.

Such hostility was, admittedly, experienced between many women who became rivals (for example, Channa and Penina at the beginning of Sefer Shemuel), but a particularly tragic aspect characterizes such a relationship between sisters, as any reader of these chapters in Sefer Bereishit senses. Sufficient proof of this is to be found in verses such as (30:1), "And Rachel was jealous OF HER SISTER," and (30:8), "A Divine struggle have I wrestled WITH MY SISTER."

The lesson learned from this one-time experience from the period of the patriarchs is formulated with regard to their descendants in the Torah's command, "You shall not take a woman as a wife after marrying her sister, as her rival." You - the descendant of Yaakov - shall not again take your wife's sister beside her, turning them into rivals, "for it is not proper… for they should love each other."

The stories of the forefathers are a teaching in themselves; they contain lessons for their descendants for generations to come - lessons which are sometimes formulated as explicit mitzvot. The life stories of the forefathers are meant to serve us - their children - as the basis for leading our lives according to the mitzvot of the Torah.

(Translated by Kaeren Fish.

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