Nedarim 27a - Nidrei Onsin

1. In the case where a person makes a stipulation with the beis din that his zechuyos should be lost if he does not show in 30 days, and fails to show up due to an o'nes, his zechuyos would be batul. The gemara questions that his zechuyos should not be batul for two reasons: 1. o'nes rachmana patrei - just as the girl who commits adultery b'ones does not qualify as committing adultery, so too the person who fails to show in court due to an o'nes does not qualify as "not showing". 2. Similar to Nedarim - his original stipulation was that if he DECIDES not to show, he should loose his zechuyos, but if an o'nes prevents him from showing then he does not loose zechuyos.

2. The Ran clearly indicates that the first approach would only work by a real o'nes that would actually prevent him from showing, but the second approach would work even by a partial o'nes, such as his son getting ill where it is difficult for him to show but not impossible.

The gemara challenges whether we can learn from na'arah ha'meurasa to other cases because "maybe regarding killing her is different". The Rosh offers 2 approaches in this distinction (see rashash for a slight yet compelling change of girsa in the Rosh). 1. we always do whatever possible to avoid capital punishment so we are more likely to use o'nes as an exemption from capital punishment than from other things ("rashi" seems to say this as well). 2. when one could have stipulated and failed to do so, we assume he included even a case of o'nes but by the adultery where she could not have stipulated on anything, the o'nes is an exemption.

3. The Ran and Rosh argue about R' Huna's logic to make a distinction between the person stipulating to be mevatel his zechuyos and the case of nidrei o'nsin. Ran says in the case of neder where the inviter is making the neder that effects the invitee, he doesn't care enough to be expected to stipulate, but when one makes a condition about themselves they are expected to stipulate. The Rosh says that the default by money matters is not to follow what he is thinking (such as the exclusion of o'nes) unless he explicitly stipulates, but by neder we follow what he his thinking if we are sure that he didn't mean to include a case of o'nes. The Keren Orah explains that the Ran and Rosh go lishatasam on 24a. They argue who is making the neder in the case of the mishna: Ran holds that the ba'al habayis is making the neder, therefore he can say that he doesn't care enough to stipulate since he is not affected by the neder. The Rosh holds that the invitee is making the neder and therefore cannot say like the sevara of the Ran since he should care enough to stipulate, therefore he has to come up with another difference between the 2 cases.