Yibbum

The Torah prohibits sexual relations by a man with his brother's wife,[1] but yibbum is an exception to this rule.

At the time the Torah was written, if a woman did not have a husband because of widowhood, she had no one to provide for her any longer and she would be disgraced, if not likely die of starvation.

[citation needed] Children were also a means of continued provision, since they are commanded to care and show respect for the elderly as they move further along in years.

Under Torah, men had a responsibility to the women around them, which included life-sustaining provisions (i.e. food, shelter, and comfort).

[3] A detailed account of a levirate-type marriage in the Hebrew Bible is the unusual union of Judah and his daughter-in-law Tamar found in Genesis 38:8.

In this case as well, the kin in question would not have been subject to the biblical levirate marriage obligation, as neither Ploni Almoni nor Boaz were brothers of Ruth's late husband.

Yibbum is an exception to the biblical prohibition for a man to have sexual relations with "his brother's wife" found for example in Leviticus 18:16 and 20:21.

[16] If all surviving brothers are still children, the widow must wait until one reaches halachic adulthood, at which time he can perform yibbum or halizah.

Nevertheless, the Sages decreed that the couple perform a marriage-like ceremony called maamar,[18] recite the marriage blessings (sheva brachot) and write a prenuptial agreement (ketubah).

Because there is a general prohibition on a man marrying his brother's wife, anytime that a yibbum is not required (for example, the deceased had a child), levirate marriage is forbidden.

[21] The Samaritans followed a slightly different course, which may indicate an earlier custom; they practised yibbum only when the woman was betrothed and the marriage had not been consummated.

[31] Additionally, if the surviving brother is married, Ashkenazim, who follow the takkanah of Gershom ben Judah abolishing polygamy, would be compelled to perform halizah.

Orthodox Jews in modern times have generally upheld the position of Rabbeinu Tam and perform halizah rather than yibbum.