Rambam - 1 Chapter a Day

The laws that apply when we do know which brother died first are stated in Halachot 3 and 4.

According to Scriptural Law, it is forbidden to marry two sisters. As an extension of this prohibition, when one is obligated to perform yibbum with two sisters according to Rabbinic Law, one is not allowed to marry either of them and must perform chalitzah with both.

For according to Scriptural Law, the obligation of yibbum applies in all these instances, as stated in Chapter 6, Halachah 10.

In Halachah 1
Yehudah, Reuven, Shimon and Levi were brothers. Reuven was married to Leah, and Shimon to Rachel. Yehudah was married to Rivkah who was the mother of Leah, Reuven’s wife. Levi was married to Sarah who was the mother of Rachel, Shimon’s wife. If both Reuven and Shimon die childless, Yehudah may perform either yibbum or chalitzah with Rachel and Levi may perform either yibbum or chalitzah with Leah. Diagram

The Kessef Mishneh (and the Beit Shmuel 175:2) explain that this ruling applies only after the fact — i.e., he performed chalitzah with the second yevamah without asking Rabbinical guidance. Had he in fact asked the Rabbis, they would have prohibited it, lest he err and perform chalitzah with the other sister. Once, however, the chalitzah is performed, we do not fear that a mistake will be made by others on a subsequent occasion.

Since he was never permitted to marry the wife of the first brother who died, the wife of the second never became forbidden to him.

Since he is not permitted to marry the wife of the second brother, the wife of the first never became forbidden to him. Hence, he should perform yibbum. Diagram

The Rambam mentions both yevamot to teach that even if the brother who marries the first yevamah dies, she remains forbidden to his brothers.

See the previous halachah.

This applies to both couples. The first yavam who marries a yevamah is forced to separate because he has transgressed a Rabbinic prohibition. Even though he did not transgress in marrying his yevamah, the second yavam is forced to separate from her, because his marriage to her was made possible by a forbidden act, the first yavam’s marriage.

This law is fundamentally the same as Halachah 3. The yavam is forbidden to perform yibbum with either of the sisters. There is one added element: the fact that a ma’amar was given.
As explained in Chapter 5, Halachot 2-3, a ma’amar does not establish a complete marriage bond. If it established such a bond, the third brother would not be required to divorce his yevamah (and he would not be required to perform chalitzah with her sister). But since it does not, he cannot consummate his relationship with his yevamah. He must, however, divorce her, because of the connection established by the ma’amar.
Reuven, Shimon, and Levi were brothers. Reuven was married to Leah, and Shimon to Rachel. Leah and Rachel were sisters. Shimon died, and Levi gave a ma’amar to Rachel. Then Reuven died. Levi must divorce Rachel and perform chalitzah with her, and then he must perform chalitzah with Leah. Diagram

As reflected in Chapter 6, Halachah 25, even if the yavam who died had not given a ma’amar to the other yevamah, this woman would not have been able to perform yibbum. The new dimension contributed by this halachah is that the ma’amar does not free her from the obligation of chalitzah.

I.e., had the ma’amar established a full marriage bond, she would not have been obligated at all. Since it does not, she must perform chalitzah.

This law applies if he consecrates her after his brother has died and the obligation of yibbum is already incumbent upon him. If he consecrated her before his brother dies, and then he dies, he may marry her (Shulchan Aruch, Even HaEzer 159:6).

At present, the woman he consecrates is forbidden to him, because he is obligated to perform yibbum with her sister. Nevertheless, he is not required to divorce her, because it is possible that the prohibition will be lifted.

Or he has no other brothers.

The fact that he was forbidden to marry her while her sister was alive does not prevent him from marrying her after her sister’s death (Beit Shmuel 159:13).

From Yevamot 41a, it appears that whenever a yavam cannot perform yibbum with his yevamah, the chalitzah he performs with her is deemed "inferior."
Reuven, Shimon, and Levi were brothers. Reuven was married to Leah and Sarah, and Shimon to Rachel and Asnat. Sarah and Rachel were sisters. Both Reuven and Shimon died. Levi thus must perform chalitzah with Leah and Asnat. This applies even if he performs chalitzah with Rachel and Sarah. Diagram

Chapter 5, Halachah 12.

This expression is employed by the Rambam in reference to a law that has no direct source in the Rabbinic works of the previous generations. The Rambam’s rationale is that just as the Rabbinic prohibition against performing yibbum with the sister of a woman to whom one is obligated is sufficient to cause a chalitzah to be considered "inferior," so too, the prohibitions mentioned in this halachah should have a similar effect.
There are several early halachic authorities who rule differently from the Rambam on this issue. The Rambam’s decision is, however, accepted by the Shulchan Aruch (Even HaEzer 174:1).

This represents a reversal of the Rambam’s opinion in his Commentary to the Mishnah (Yevamot 3:7), where he states that the deceased’s other wife should perform chalitzah, because there is a doubt whether or not an obligation falls upon her.

For the prohibition forbidding a woman divorced by her husband to her yavam is of Scriptural origin, while her remarriage is binding according to Rabbinic Law alone.
Reuven, Shimon, and Levi were brothers. Reuven was married to Leah, Shimon to Rachel, and Levi to Asnat. Leah and Rachel were sisters. Shimon died and Levi performed yibbum with Rachel. Leah, Reuven’s wife then died. Afterwards, Levi died. Both Rachel and Asnat are free of the obligation to perform either chalitzah or yibbum.
The Ra’avad and Rabbenu Asher rule that the minor must perform chalitzah when she attains majority. The Ma’aseh Rokeach states this might also be the Rambam’s intent (as reflected by the fact that he states that "she is forbidden to her yavam," and in the next halachah he adds that she "should not perform either chalitzah or yibbum’’). Most commentaries do not, however, accept this interpretation. Diagram

The Rambam’s wording is somewhat imprecise. The kiddushin the husband gives the father are binding according to Scriptural Law, because the Torah granted him the right to consecrate her, as stated in Hilchot Ishut 3:11. If the girl is able to distinguish between a get and another object, she can be divorced according to Scriptural Law, as stated in Hilchot Gerushin 2:19.

Until she reaches the age of twelve and manifests signs of physical maturity, she is not able to bring about kiddushin that are binding according to Scriptural Law. (Moreover, the girl’s father also does not have the potential to consecrate her again according to Scriptural Law once she has been divorced, as stated in Hilchot Ishut 3:12.)

In this instance as well, the divorce is binding according to Scriptural Law, while the remarriage is merely a Rabbinic institution.

Since the remarriage of the minor or the deaf-mute is only a Rabbinic institution, while the marriage of the deceased’s other wife is based on Scriptural Law, the remarriage of the minor or the deaf-mute has no effect on the other wife’s obligation to her yavam. See Shulchan Aruch (Even HaEzer 173:23).

If her husband engaged in marital relations with her after she attained majority or regained control of her faculties, he acquires her as a wife according to Scriptural Law. (See Hilchot Gerushin 11:6.) Therefore, there is no difference between her and another woman who was married, divorced and remarried.

Since both sisters share the same status, we allow the marriage of the sister whose husband is alive to continue. There is no mandate for him to perform yibbum, for the marriage to his yevamah would still be Rabbinical in origin.

Since the marriage of the older sister is binding according to Scriptural Law, the younger sister has no obligation to the yavam.

The yibbum of the older sister is given priority over the marriage of the younger sister, because the older sister’s first marriage is binding according to Scriptural Law, and the obligation of yibbum is mandated by that authority. The marriage of the younger sister, by contrast, is binding only according to Rabbinic Law. Therefore, the younger sister is advised to perform mi’un, thus dissolving her marriage as if it had never existed. At this point, there is nothing preventing her husband from marrying her sister, his yavam. (See Chapter 4, Halachah 30.)

As long as one of the parties involved is a deaf-mute, a marriage is binding only according to Rabbinic Law. For this reason, there is no advantage for the yibbum of the deceased’s wife over the existing marriage.

Since both the husband and wife are mentally competent, their marriage is binding according to Scriptural Law. The deceased’s wife is, therefore, freed of all obligations.

And it is forbidden to marry the sister of a woman with whom one is obligated to perform yibbum.

For it is forbidden to marry the sister of one’s divorcee.

See Chapter 4, Halachah 13.

I.e., the court, the agent of the Jewish people as a whole, does not have the responsibility to admonish a child who violates the Torah’s laws. The child’s parents, by contrast, do and must train him in the observance of the Torah’s ways. See Hilchot Ma’achalot Asurot 17:27-28.

Since both partners are mentally competent, their marriage is binding according to Scriptural Law.

Since his marriage to the deaf-mute is only a Rabbinic institution, his obligation to the wife of his deceased brother, a requirement of Scriptural Law, takes priority. Nevertheless, since he must divorce his deaf-mute wife with a get, he may not perform yibbum, for the yevamah is the sister of his divorcee.

In contrast to the deaf-mute yavam mentioned in Halachah 18.

I.e., one might think that although the mitzvot of yibbum and chalitzah do not apply with regard to the woman forbidden as an ervah, they do apply with regard to her deceased husband’s other wife.
Generally, when a woman is forbidden as an ervah, her husband’s other wives are not obligated, as stated in Chapter 6, Halachah 14. Nevertheless, since the deaf-mute’s marriage is only a Rabbinic institution, one might think that the marriage to the woman forbidden as an ervah is not powerful enough to negate the obligation of yibbum. The Rambam’s explanations that follow above are intended to counter this supposition.
Reuven and Shimon were brothers. Shimon was a deaf-mute. Rachel, Shimon’s daughter married Reuven as did Leah, a woman with no family connection to him. Reuven died childless. Both of his wives are free from the obligations of yibbum and chalitzah. Diagram

I.e., any other woman permitted to his brother, but forbidden to him as an ervah. This includes the brother’s mother-in-law and his daughter-in-law, after they were widowed or divorced from their first husbands.

If it were a fully binding marriage, the deceased’s other wife would be freed of the obligation of chalitzah as well, as mentioned in note 40. Nevertheless, yibbum is not permitted because the marriage is effective according to Rabbinic Law.