Why include an impossible yavam in yibum?

Question

R. Akiva states (Y'vamos 8:4) that there is a distinction between the levirate obligations of an impotent man who has been that way all his life and an impotent man who became that way during his lifetime. Namely, the latter has a levirate status (which he is required to sever, but that's beside the point) because there was a time that he could father children and the former doesn't because he was never in a physical state conducive to fulfillment of yibum.

Rava explains (79b) that it need not be that the man is physically qualified right now, just that he was ever qualified. This is based on the fact that the same qualifications apply to both the deceased, who triggers the obligation, and the surviving brother, who fulfills it.^{[citation needed]} And every deceased person had some period of time immediately before death in which they were physically unqualified to conceive children, due to the circumstances that near-death entails. Disqualifying such people would mean ineffectuating the mitzva of yibum, so it can't be what the Tora had in mind.

Why does R. Akiva's opinion allow a s'ris adam on the grounds of having had a sh'as kosher at an irrelevant time in the past before he was married? It could have allowed only those sarisim who had a sh'as kosher at a relevant time, thus excluding a yavam who had no sh'as kosher while his zika was active.

Answer 1

In the lecture of Mishna we still don't know the type of Saris, but we see an equivalence:

לא חולץ <=> ולא חולצין לאשתו

So, if someone became Saris and die without children, לא חולצין לאשתו.

The reason for the לא חולצין לאשתו is the Derasha לא ימחה, פרט למי ששמו מחוי Gemara 24a.

If the brother of the died husband is Saris, he have not to make Chalitsa.

The reason for the לא חולץ is the Derasha להקים לאחיו ולאו בר הכי הוא Gemara 79b.

However, it turns out that every man, a few time before his death becomes Saris Adam. So if the type of Saris for whom לא חולץ ולא חולצין לאשתו is Saris Adam, there is no more issue for Mitsvat Ybum and Chalitsa.

In this reasoning, there is a problem. If the Saris who doesn't make Chalitsa and his brother doesn't make Chalitsa to his wife, we have a false inference. Because we know from the fact that Mitsvat Ybum and Chalitsa exist, that every husbands is Saris Adam before the Mitsva, and despite that, his brothers have to make Chalitsa or Ybum. So, to solve this problem, we rule that equivalently to the rule for the dead husband, a Yabam Saris Adam have to make Chalitsa.

If you ask for the logic. The same logic as for the husband. Why need we to be worry for a man who became Saris and died without children. Because he had a Shaat Hacosher. since we have Shemo Machuy that is neglected because Sheat Hacosher, Lav bar Hakamat shem is neglected because of Sheat Hacosher.

The question of the OP seems to underline the Svarat Hacholkim. First, the Husband was a normal man, ha was not Saris, before the death process he was fertile.

כחישותא הוא דאתחילה ביה - רש"י ולאו סריס הוא אלא מיתה מכחשת כחו

It is only a general state of debility that had set in.

So, Ein Shemo Machuy. And this Derasha is not a problem for a common dead husband.

Equivalently, we don't need to change the pashtut of the Derasha of Derasha להקים שם לאחיו to establish a name for his brother, that needs a possible fertility.

So, the Yabam have to be fertile. Or will possibly become fertile.

In summary, you say that the svara of Rabbi Eliezer is more understandable. The learning of Rabbi Akiva is more formal. But logically, the strength of the Derasha of Rabbi Akiva is that we cannot easily skip the pashtut of פרט למי ששמו מחוי .