We all know that levud is a halacha l Moshe MiSinai. Is there a machlokes haTanaim as to whether it is a minmum of three or four tefachim as to its shiur and if so, how can we say so in a halacha lmoshe misiai?
The Gemara in Eruvin (end of 4b) says that Lavud is a Halachah le'Moshe mi'Sinai. You are correct that the Shi'ur of Lavud is subject to a Machlokes Tana'im. Raban Shimon ben Gamliel maintains that the principle of Lavud is operative up to a Shi'ur of four Tefachim, and the Chachamim maintain that Lavud works until three Tefachim (and the Halachah follows the Chachamim).
You are asking a good question, how can there be a Machlokes about something which is a Halachah le'Moshe mi'Sinai such as Lavud, since the Rambam writes (in his introduction to Perush ha'Mishnayos, and in Hilchos Mamrim ch. 2) that there was never a dispute concerning a Halachah l'Moshe m'Sinai.
The CHAVAS YA'IR (#192) asks this question, and he even mentions this Machlokes between Raban Shimon ben Gamliel and the Chachamim as an example of a Machlokes regarding a detail of a Halachah le'Moshe mi'Sinai (192:6). The Chavas Ya'ir attempts to prove at great length that the Rambam is incorrect, as do many other Acharonim.
(It could be that the Rambam did not mean that no Halachah l'Moshe mi'Sinai was ever subject to dispute, but that certain Halachos are agreed upon by all, even though the Tana'im seem to argue as to their source in the Torah -- the examples the Rambam brings are such Halachos, e.g. Esrog=Pri Etz Hadar and Bas Kohen Ki Sizneh=Eshes Ish. Alternatively, the Halachah l'Moshe m'Sinai did not specify the exact amount of Tefachim Lavud pertains to, but that there is such a thing as Lavud altogether. The Chachamim then argued over how to apply the law of Lavud.)
In Shiurim Lzecher Abba Mori ( chelek rishon) , Rav Soloveitchi z'l developed an entire shiur on a .very similar topic entitled "Shnei Sugei Msores" which touches somewhat on this issue. The Encyclopedia Talmudit has a long entry under the subject of machlokes and Halacha lMoshe MiSinai with many mekoros on this issue as well.
Thank you for those references. The Encyclopedia Talmudis cites the answer that we wrote -- that the specific details of some Halachos le'Moshe mi'Sinai can be subject to Machlokes -- in the name of the Kreisi u'Pleisi (29:3), Rav Shlomo Raphael Yehudah Lewin and others.
Rav Yehudah Landy explained to me that another standard answer for the Rambam's rule is that there only is agreement that a Halachah l'Moshe mi'Sinai exists, and was handed down. What exactly the HLM said may be debated, as long as it is agreed that there is a HLM on the subject.
Regarding understanding the Rambam's approach to Halacha l'Moshe mi'sinai it is worthwhile reading Rav Zvi Lampel's sefer "The Dynamics of Dispute" Judaica Press NY 1992. A good part of the book is devoted to this Rambam.
Dear Rabbi Kornfeld:
The Rambam's statement that there can't be a Machloches in a Halacha L'Moshe M'Sinai....
and the CHAVAS YA'IR (#192)'s objection based on the numerous instances of HLM where we find Machlokes (eg. the Machlokes between Raban Shimon ben Gamliel and the Chachamim, whether the Shiur of Lavud is 3 or 4 Tefachim)....
and the "standard answer" that the Rambam only means that there will always be agreement that a Halachah l'Moshe mi'Sinai exists, and was handed down. What exactly the HLM said, may be debated, as long as it is agreed that there is a HLM on the subject....
and the question whether HLM are D'Oraysa or D'Rabanan.
I believe that the "standard answer" you refer to is the explanation of the Chikrei Lev and elaborated upon by the Maharatz Chayes (Yoma 80a). Many HLMs were given at Sinai in general terms only, while the details and application were left for the Rabbis to decide. Take for example Shiurim. The general principal is that there is a Shiur of CZayit and a Shiur of Kosevet. However it was not ordained at Sinai that Kosevet is the Shiur for Yom Kippur and CZayit is the Shiur for other Issurim. The application was left for the Rabbis to make. With respect to the general terms there will never be a Machlokes. However with respect to the details and application there certainly are disputes (for example Lavud - 3 or 4).
It occurs to me that this idea is alluded to in the Sugiah in Eruvin (4b) which brings Psukim as the source for Shiurim. The Gemorah however concludes - "Do you really think that Shiurim are written in the Torah? (Of course not). Rather, they are HLM, which were later given Scriptural support (Esmachta) by the Rabbis". According to this Gemora, Shiurim are definitely HLM.
However, the Gemorah in Brochos (41b) says they are only of Rabbinic origin: "These Shiurim, are they really written expicitely in the Torah? (Of course not). Rather they are D'Rabanan, and the Psukim are just an Esmachta". Rav Yeshaya Berlin (Pik), in his glosses, points out the contradiction.
I believe that there is no contradiction. The two Gemorahs are talking about two different aspects of HLM. The Germorah Eruvin is talking about the general principal of Shiurim - that there are Shiurim of KZayit and Kosevet is indeed HLM. The Gemorah in Brachos is refering to the application - that Kosevet is used for Yom Kippur and KZayit for other Issurim - that is D'Rabanan.
Thank you! Benny, your comments are excellent. (What you mention as the "'standard answer' that... what exactly the HLM said, may be debated, as long as it is agreed that there is a HLM on the subject," is different than the explanation that we wrote, which was that the Halachah was transmitted to Moshe at Sinai, but certain details, such as the Shi'ur, were not transmitted, and the Torah left that to the Chachamim to establish. Thus, the disputes do not involve any part of what was transmitted as Halachah le'Moshe mi'Sinai. The disputes involve the parts left to the Chachamim to decide.
It is worthwhile to note that in the verse it is written only the size of the Shi'urim, and there is no allusion to which Halachos they apply. On that which is written in the verse the Gemara says "it is d'Rabanan" (i.e. the Shi'urim themselves) while according to what you write, that which is written is indeed a HLM. If so, we must explain the words "it is d'Rabanan" to mean that it is something which was transmitted Ba'al Peh to the Rabanan.)
Could we not say that the basic question of whether there are shiurim is answered by the HLM, and the particular Shiurim and their application was left for the Chachamim to determine.
From the point of view of those who believe that "Hatsi Shiur Asra Tora" - the Tora prohibitions are absolute, without lower limit - the HLM recognizes that this is normative but unlivible, and tells us that we are not responsible for minute quantities. How small is "Minute" - this was determined by the Chachamim, based on reason, analogy and D'rash. Those who disagree that "Hatsi Shiur Asra Tora" would say that the the HLM tells us that Tora only forbade meaningful quantities; how big is "Meaningful"? - This was determined by the Chachamim, based on reason, analogy and D'rash.
Does this seem reasonable?
Your insights sound reasonable. Thank you for sharing them with us.