I apologize if this is a very elementary question, but I'm having trouble finding an answer to it. As we all know, there are many kinds of marriages which one can generally term "halachically disallowed" (incestuous, Jew and non-Jew, mamzer and non-mamzer, kohen and convert, kohen gadol and widow, etc.).

I'd like to know which of these are invalid (in the sense of halachic impossibility: any attempt by the people in the relevant categories to get married is just void ab initio and has no legal force) and which are forbidden (in the sense that a marriage can in fact occur, assuming other ordinary conditions are met, but it will be an aveira and those involved will be duty bound to divorce). The distinction is often not really made clear in secondary sources.

One example I do know about involves polygyny: excluding Yemenites, after the takana of Rabbeinu Gershom, it's forbidden for a married man to marry, but if he does, it's still a valid marriage and requires a get for its dissolution. But what about, e.g., the marriage of a kohen and a convert?

  • 5
    This is not an elementary question at all, +1.
    – Scimonster
    Dec 31, 2014 at 8:07
  • Okay, after looking further, m. Kid. 4:12 seems to answer the validity question positively in the case of forbidden marriages involving mamzerim and kohanim and negatively in cases of incest and intermarriage, which is pretty much what I would have guessed. But if that's an oversimplification, please do let me know.
    – Alix
    Dec 31, 2014 at 8:31
  • There is another category, of "forbidden but valid" in which the couple may remain together b'dieved. I mention one case in a comment on @DannySchoemann's post and I think his examples overlap with this category a bit, too (i.e. where the children would be simply "blemished")
    – SAH
    Mar 6, 2018 at 22:54

2 Answers 2


The source is a Mishna (Kidushin 3:12) which states that if Issur Karet is involved (excluding Niddah) then the Marriage is invalid (i.e. they are not married). Any offspring of such a union would be Mamzerim.

A list of these is in Vayikra Ch 18 and pasted below. (That's in אַחֲרֵי מוֹת; the Kriat HaTorah for Yom Kippour afternoon.)

Marrying a non-Jew is forbidden, and the marriage is invalid, as the Rambam says in הלכות אישות - פרק רביעי

טו: הַמְקַדֵּשׁ כּוּתִית אוֹ שִׁפְחָה אֵינָן קִדּוּשִׁין אֶלָּא הֲרֵי הִיא אַחַר הַקִּדּוּשִׁין כְּמוֹ שֶׁהָיְתָה קֹדֶם הַקִּדּוּשִׁין. וְכֵן עַכּוּ''ם וְעֶבֶד שֶׁקִּדְּשׁוּ בַּת יִשְׂרָאֵל אֵין קִדּוּשֵׁיהֶן קִדּוּשִׁין. יִשְׂרָאֵל מוּמָר שֶׁקִּדֵּשׁ אַף עַל פִּי שֶׁהוּא עוֹבֵד עַכּוּ''ם בִּרְצוֹנוֹ הֲרֵי אֵלּוּ קִדּוּשִׁין גְּמוּרִין וּצְרִיכָה גֵּט מִמֶּנּוּ:‏

In all other forbidden cases, the marriage is valid, yet forbidden. Some forbidden marriages cause the offspring to be mamzerim, some to be Chalalim and some to simply be blemished.

Source: Rambam הלכות אישות - פרק ראשון

List of Karet-unions; marriage not possible.

ז: עֶרְוַת אָבִיךָ וְעֶרְוַת אִמְּךָ לֹא תְגַלֵּה אִמְּךָ הִוא לֹא תְגַלֶּה עֶרְוָתָהּ: ‏ - Parents

ח: עֶרְוַת אֵשֶׁת אָבִיךָ לֹא תְגַלֵּה עֶרְוַת אָבִיךָ הִוא: ‏ - Father's wife

ט: עֶרְוַת אֲחוֹתְךָ בַת אָבִיךָ אוֹ בַת אִמֶּךָ מוֹלֶדֶת בַּיִת אוֹ מוֹלֶדֶת חוּץ לֹא תְגַלֶּה עֶרְוָתָן: ‏ Sister

י: עֶרְוַת בַּת בִּנְךָ אוֹ בַת בִּתְּךָ לֹא תְגַלֶּה עֶרְוָתָן כִּי עֶרְוָתְךָ הֵנָּה: ‏ Granddaughter (and daughter)

יא: עֶרְוַת בַּת אֵשֶׁת אָבִיךָ מוֹלֶדֶת אָבִיךָ אֲחוֹתְךָ הִוא לֹא תְגַלֶּה עֶרְוָתָהּ: ‏ Step sister (Father's wife's daughter)

יב: עֶרְוַת אֲחוֹת אָבִיךָ לֹא תְגַלֵּה שְׁאֵר אָבִיךָ הִוא: ‏ Father's sister (Aunt)

יג: עֶרְוַת אֲחוֹת אִמְּךָ לֹא תְגַלֵּה כִּי שְׁאֵר אִמְּךָ הִוא: ‏ Mother's sister (Aunt)

יד: עֶרְוַת אֲחִי אָבִיךָ לֹא תְגַלֵּה אֶל אִשְׁתּוֹ לֹא תִקְרָב דֹּדָתְךָ הִוא: ‏ Father's brother (Uncle) and his wife

טו: עֶרְוַת כַּלָּתְךָ לֹא תְגַלֵּה אֵשֶׁת בִּנְךָ הִוא לֹא תְגַלֶּה עֶרְוָתָהּ: ‏ Daughter-in-law

טז: עֶרְוַת אֵשֶׁת אָחִיךָ לֹא תְגַלֵּה עֶרְוַת אָחִיךָ הִוא: ‏ Brother's wife (except for Yibum)

יז: עֶרְוַת אִשָּׁה וּבִתָּהּ לֹא תְגַלֵּה אֶת בַּת בְּנָהּ וְאֶת בַּת בִּתָּהּ לֹא תִקַּח לְגַלּוֹת עֶרְוָתָהּ שַׁאֲרָה הֵנָּה זִמָּה הִוא ‏ Mother and daughter

יח: וְאִשָּׁה אֶל אֲחֹתָהּ לֹא תִקָּח לִצְרֹר לְגַלּוֹת עֶרְוָתָהּ עָלֶיהָ בְּחַיֶּיהָ: ‏ Sisters, if first wife-sister is still alive.

(יט: וְאֶל אִשָּׁה בְּנִדַּת טֻמְאָתָהּ לֹא תִקְרַב לְגַלּוֹת עֶרְוָתָהּ: ‏ Nidda. Not included.)

כ: וְאֶל אֵשֶׁת עֲמִיתְךָ לֹא תִתֵּן שְׁכָבְתְּךָ לְזָרַע לְטָמְאָה בָהּ: ‏ Married to another.

  • 1
    "Some forbidden marriages cause the offspring to be mamzerim," even if kiddushin is chal (the marriage "works")? Which erva (forbidden relation) does that?
    – GFauxPas
    Dec 31, 2014 at 19:04
  • 2
    @GFauxPas - I'm not sure I like the equation erva=forbidden relation. To answer your question: Some forbidden marriages - e.g. Kosher Jews marrying a Mamzer - cause the offspring to be mamzerim. Jan 1, 2015 at 7:26
  • 1
    @DannySchoemann There are other issurei karet not listed in the paseukim, particularly your daughter (kal vachomer from your granddaughter).
    – Chanoch
    Jan 1, 2015 at 11:03
  • You also can't be married to a slave.
    – Ypnypn
    Jan 1, 2015 at 21:55
  • 1
    @DannySchoemann That's only a Jewish slave, and even he isn't really married to her.
    – Ypnypn
    Jan 4, 2015 at 19:54

Just in shorter form: basically, immediate relatives and non-Jews -- no marriage at all. Other prohibitions -- yes marriage, though prohibited.

  • 1
    Inaccurate. Already married women are not immediate relatives. It's also not a term usually used for a wife's sister, a daughter-in-law, an aunt. Besides, one may marry a niece. Jan 1, 2015 at 7:36

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .