More Discussions for this daf
1. Kidushei Cheresh 2. The Din of a Katan 3. Aba Shaul

Ira Slotnick asked:

In all these cases where one is a Pikeyach and one a Cheresh, what are the underlying principles differentiating halacha the healthy brother/sister versus the unhealthy brother/sister.

The Kollel replies:

Whenever either of the couple are deaf-mute, the Kidushin is d'Rabanan. Therefore the resulting Isur of Achos Isha is d'Rabanan and the ensuing Yibum is d'Rabanan.

(A deaf-mute can only perform Yibum and not Chalitzah.)

The complication arises when a "healthy" brother who is married to a "healthy" sister dies, which requires his brother to do Yibum mid'Oraisa. Had the brother's marriage to his Yevamah's sister been d'Oraisa as well, his Yevamah would then be Peturah from Yibum and Chalitzah for she would be Achos Isha, one of the fifteen women mentioned at the onset of the Meseches.

But when either the Yavam or his wife is "unhealthy" he must be Meyabem her sister for she is an Ervah only mid'Rabanan. Therefore he must divorce his wife (if possible). Even so he may not be Meyabem his ex-wife's sister for mid'Rabanan she is an Achos Isha and therefore he must give Chalitzah (if possible.)

Dov Zupnik