On yesterday’s daf we learned of the concept of zika – a connection between the potential yavam and yevama that creates almost a relationship of marriage between them. The idea of zika is used by our Gemara to explain the contrarian position of Rabbi Shimon in our Mishna (18b).
Thus far in Massekhet Yevamot we have accepted that the case of eishet ahiv she-lo haya be-olamo – when there is a brother who was not born until after the woman became a widow – is not included in the mitzva of yibum (see daf 17); thus, in such a situation, neither the widow nor her tzara (fellow wife) could become the yevama of such a brother. In our Mishna (18b), however, we learn that Rabbi Shimon requires either yibum or halitza in just such a case.
The Gemara explains that, according to Rabbi Shimon, an example of eishet ahiv she-lo haya be-olamo will be when a man with no brothers passes away with no children. Any brother born after his death will be considered an eishet ahiv she-lo haya be-olamo. If, however, there was a living brother at the time that the first brother dies, and that brother performs yibum, when a new brother is born we view the yevama as the full wife of the living brother, and so the prohibition of eishet ahiv she-lo haya be-olamo would not apply should the present husband die with no children.
Rabbi Oshaya goes one step further in the Gemara, arguing that even if the yavam had not yet taken the widow as his yevama at the time that the newborn brother arrived, nevertheless because of the rule of zika we consider them already married, so Rabbi Shimon would not consider this a case of eishet ahiv she-lo haya be-olamo.
Abaye points to an obvious difficulty with applying zika in this fashion. What if there are two surviving brothers when the first brother dies? How can Rabbi Shimon consider the yevama “married” to both of them based on the rule of zika?
In truth, although it is simpler to understand how zika works when there is only one yavam, the rishonim suggest that zika to more than one yavam means that as long as the potential exists for yibum to take place between people, we consider all of the prohibitions that stem from a marital relationship to be in place, even as it is clear that no true marriage exists.