American Reform Responsa
142. Marriage with a Mother’s Sister or Half-Sister (Aunt or Half-Aunt)
(Vol. XXXIII, 1914, pp. 59-60)
QUESTION: A couple came to me saying they would like to marry each other, but there was some degree of consanguinity concerning which they were worried. This is the situation: the young lady is a half-sister, on the father’s side, of the young man’s mother. In other words, she is a half-aunt, so to speak. Now, does the law in Leviticus forbidding marriage with a mother’s sister extend also to the half-sister? And is there no way of permitting such a marriage as we permit the marriage between an uncle and a niece?
ANSWER: The law in Leviticus is understood by all authorities to extend to the half-sister also, and there is no way to permit such a marriage according to Jewish law. The argument implied in your question–i.e., why distinguish between a marriage between uncle and niece and one between aunt and nephew–would rather tend to prohibit the former than to permit the latter. Indeed, all the Jewish sects–Samaritans, Sadokites, Falashas, and Karaites–prohibit the marriage between an uncle and a niece. And the permission or recommendation by the Talmud of a marriage between uncle and niece was probably intended as a protest against the interpretation of this law as given by the Sadducees and Samaritans (comp. S. Krauss, “Die Ehe zwischen Onkel und Nichte,” in Studies in Jewish Literature, issued in honor of Dr. Kohler at his seventieth birthday, Berlin, 1913, pp. 165-175). It is noteworthy that in spite of the approval of such a marriage between uncle and niece by the Talmud and Rabbinic authorities, Sefer Chasidim (ed. Wistinetzki, no. 1116) declares that such a marriage will not be successful, which is but another way of discouraging or disapproving of it.
Jacob Z. Lauterbach and Committee
S.B. Freehof, “Marriage with a Half-Aunt,” Modern Reform Responsa, pp. 100ff.