To sum up yesterday’s long post: there is a din of “ma’achilin lo ha’kal ha’kal techila” that obligates one to opt for the lesser evil when faced with a choice of what to feed a choleh whose life is in danger. The gemara presents a machlokes as to whether terumah or tevel is the lesser issur. The case seems very strange -- why not just seperate terumah from the tevel and make it permissible (chulin)? We discussed two approaches as to why that is not an option:
1) Rashi: there is one pile of wheat that has exactly enough grain to bake what the choleh requires. If terumah is taken off, you haven't avoided an issur because the choleh will have to eat chulin + the terumah anyway. The debate is whether it’s still preferable to do the hafrasha and eat the terumah, or to just eat tevel?
2) Parashas Derachim interpreting the Ran: there are two piles of wheat, one of tevel one of terumah. The only reason the tevel cannot be turned into chulin is some external technical reason, e.g. the owner of the wheat did not give permission for hafrasha.
The Parashas Derachim writes that his approach helps resolve another difficulty. If the only obstacle to hafrasha is the fact that the choleh has to eat everything, why not be mafrish terumah and then mix it back in to the pile so it is bateil? “Ain mevatlin issur l’chatchila” is just an issur derabbanan, and here, faced otherwise with issurei d’oraysa, it seems the best way out. The case must be that the tevel cannot be fixed for some other technical reason.
Just to add fuel to the fire, I was bothered by another point. Since separating even one stalk of wheat is sufficient to fulfill the chiyuv d’oraysa of terumah, according to Rashi why not separate a tiny portion of terumah which would only be a chatzi shiur if eaten by the choleh?
The Avnei Milu’im (in the Shu”T, #18) argues against this Parashas Derachim. As we read in Parshas Korach, terumah requires “shemira” (“mishmeres terumosai”). It cannot be destroyed, used improperly, or made tamei. Ordinarily ain mevatlin issur l’chatchila is a din derabbanan, but when it comes to terumah, since bitul causes terumah to lose its identity and sanctity, it violates this d’oraysa halacha of shemira.
And to put my fire out as well: Rav Yosef Engel writes that even those who hold that eating chatzi shiur is derabbanan agree in the case of terumah that it is d’oraysa – ingestion by a zar would effectively destroy the terumah and therefore also be a violation of shemira.
Whether this chiddush of the Avenei Milu’im is correct is a major debate in Achronim. The Steipler in his Birchas Peretz on chumash is not convinced that bitul or loss of kedusha can be equated with destruction. Others offer alternative reasons why bitul would not work in this case, e.g. terumah is property of the kohen, and bitul does not work in the realm of dinei mamonos (arguing that the dollar you owe me is bateil to the rest of the money in your wallet and therefore doesn't have to be paid back just doesn’t work).