sfeika derabbanan l'kula (III) and halacha k'divrei hameikel

This post in a continuation of the discussion started here and continued here, so take a look there first! We left off with a question on the Ran: in the case of grinding spices the Ran subscribes to Tosfos’ sevara that you do not apply sfeika derabbanan l’kula when opposing opinions have both a kula and chumra, yet the Ran is still troubled by why we do not apply the rule of sfeika derabbanan l’kula to reject both versions of R’ Nachman’s statement requiring haseiba by 2 of the 4 kosos – if haseiba is not required for the first 2 kosos, it must be required l'chumra for the last 2, and vica versa, so tbased on the Ran's own reasoning he should agree that the rule of sfeika derabbanan l’kula does not apply?

The Bais haLevi explains that there are two distinct rules that get muddled together as one. One rule is sfeika derabbanan l’kula – if there is an ambiguity as to whether the ma’aseh mitzvah derabbanan has been performed properly (or been performed at all), or a halachic question as to the parameters of a mitzvah derabbanan, a doubt is insufficient to create a halachic obligation. There is a second unrelated rule that pertains to cases where there is a dispute among Tana’im or Amoraim as to what the parameters of a din derabbanan are. The gemara (A”Z 7) tells us that with respect to dinei derabbanan we say halacha k’divrei hameikel – the halacha follows the most lenient view. A machlokes, says the Bais haLevi, is not the same as a doubt, a safeik. We may be in doubt as to which view is correct, but that is not the same as an ambiguity inherent in the mitzvah itself or the way one performed it.

Tosfos’ rule that we cannot pasken like on side l’kula if it means implicitly accepting a chumra is part and parcel of the rules of psak – it is a qualification of the rule of halacha k’divrei hameilel. However, it has nothing to do with the rule of sfeika derabbanan l’kula.

The Bais haLevi argues that the gemara of 4 kosos, where the issue is not choosing which of 2 opinions to rule in accordance with, but simply a question of determining the correct version of what a single Amora, R’ Nachman, actually said, calls for an application of the rule of sfeika derabbanan l’kula, not halacha k’divrei hameikel. Even if there is chumra as well as kula implications, we have a right based on sfeika derabbanan l’hakeil to pasken like both kulos simultaneously (if not for the fact that doing so would eliminate the mitzvah of haseiba).

The Bais haLevi used this logic to take aim at those who wished to be lenient regarding shmita based on the following reasoning – since there is a dispute between the Rambam and the Geonim regarding the correct count of years, and shmita is derabbanan, therefore on any given year we could say sfeika derabbanan l’kula and not observere shmita. Using sfeika derabbanan l’kula in this way, notes the Bais haLevi, would result in cancelling a mitzvah, so the rule does not apply. Secondly, the proper rule to apply to a dispute should be halacha k’divrei hameikel, but that rule too does not apply where each opinion has a chumra of keeping a certain year as shmita along with a kula of rejecting the count of the opposing opinion.