Why do Rashi and the other Meforshim explain the case of the Kohen who must give his Yevomo-the-Gerusha chalitza as a case of where his brother married her beIssur: Isn't it possible that the brother was a chalal (ie, from a different mother) and actually was mutar to her? I guess it would just be pushing the issur back a generation, but is this not a possibility?
With thanks, respectfully,
R.A.
RAA, NY, USA
1) This question is asked by the Aruch la'Ner. He does not give an answer. In addition, the Rashash here explains differently from Rashi and writes that, indeed, the deceased brother was a Chalal.
2) However, I think you have hinted at the fact that the brother being a Chalal is merely a different possibility and an Isur would anyway have been transgressed for the brother to be a Chalal. Therefore, there is not a clear advantage in saying that the Isur was done by the brother rather than the father. So I think we can answer the question of the Aruch la'Ner and say that Rashi chose a simpler case: where the prohibition was transgressed more recently, and in addition we do not have to invent a new scenario and say that he was a brother from a different mother.
3) After looking further into your question, I found that you were Mechaven to the Tiferes Yisrael, bs'd:
The Tiferes Yisrael (#22) writes that either the brother married her b'Isur, or the brother was a Chalal. We see that they are both possibilties, and that Rashi is giving only one of the possibilities.
The Tiferes Yisrael does not appear to be too disturbed by the question of the Aruch la'Ner since it is quite acceptable that Rashi does not list all the possible scenarios.
Kol Tuv,
Dovid Bloom