I've heard that the children of two sisters are like siblings spiritually. If a woman gives her son to marry her sister's daughter this is forbidden, correct?

Does this make the union incest and the children of such a union mamzerim? Even if it was very common to marry cousins in the shtetls of Europe?

But the first-cousins who married -- their mothers were sisters.

  1. Halachically, are the children of such unions mamzerim?
  2. If a mamzer is unaware of his or her status and marries a regular Jew and has children with this Jew, are their children mamzerim?
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    Welcome to MiYodeya Temima. Great to have you learn with us! – mbloch May 29 '18 at 12:56
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    Can you source I've heard that the children of two sisters are like siblings spiritually? Never heard of that. – Danny Schoemann May 29 '18 at 13:12
  • Your second question is unrelated to your first question, and therefore should probably be asked in a separate post. – Alex May 29 '18 at 17:25

Marriage between first cousins are allowed in Judaism.

aish.com writes explicitly

It is permitted under Torah law for cousins to marry. In fact, the Sages seem to view marriages between relatives as desirable. The Talmud recommends that a person marry his niece (Yevamot 62b). [...] The assumption is that a person will have an especially close relationship with a close relative, perhaps because of their likely similar personalities and values. The reasoning may be the same for a cousin, but the Talmud doesn't mention it. (I should point out that for a woman to marry her nephew is forbidden from the Torah – Leviticus 18:12-13.)

Some point out that the daughters of Zelophehad married their cousins (Numbers 36:11) so the practice has good precedent. [...]

In terms of the genetic issues, [...] relatives who marry should be even more careful to do genetic screening in advance.

Note that a number of countries and US states forbid first-cousin marriage though.

Mamzerim are the children of an adulterous or incestuous union (e.g., a man and a married woman or of a brother and sister - but NOT of a man to to an unmarried woman). Any decisions on the status of their children need to be considered by a qualified rabbi as there might be ways to disqualify the marriage (e.g., on technical grounds) and avoid the mamzer status.

  • Hi- thank you but I am asking specifically about first cousins WHOSE MOTHERS ARE SISTERS, not "can cousins marry in general?". There is a difference in status to different kinds of cousins. That is why it is ok for a man to marry his niece but it is forbidden for a woman to marry her nephew. I'd like to know if anyone knows the source of two sisters' children being like siblings spiritually? Thanks. – Temima123 May 30 '18 at 13:50
  • I also understand that mamzerim are from any forbidden relationship in the Torah (ie: a brother raping a sister, chas v;shalom) and not only from an adulterous married woman. – Temima123 May 30 '18 at 13:52
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    @Temima123 There is no difference in the halacha of getting married between cousins whose mothers are sisters, or other cousins. If you want to know the source of two sisters children being spiritually like siblings, you should ask a new question. Here it was your hypothesis. I personally have never heard of that – mbloch May 30 '18 at 14:35
  • @Temima123 yes mamzerim are broader - I was just giving two examples – mbloch May 30 '18 at 14:35
  • Are you a rabbi? What is your source, please? – Temima123 May 31 '18 at 19:06

received an answer from Rabbi David Sperling of yeshiva.co:

Shalom, Thank you for your question. First cousins are allowed to marry according to Jewish law. The children of two sisters (i.e. first cousins) are permitted to marry, and therefore there is no question at all of any mamzer status applying. [However one should be aware that there are genetic issues involved in such a marriage – and one would be advised to seek genetic testing etc before such a union.] I am unaware of any source that equates cousins of siblings.

In regards to your second question – the law is that an unknown (or even doubtful) mamzer is not a mamzer at all. That is, it is not that they are an “unknown mamzer”, but one of the laws of a mamzer is that until the mamzer status is clarified beyond doubt, there is no mamzer at all.

Thank you to all who responded!

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