Is the Oral Law from Sinai considered d'oraisa or d'rabbanan?

Question

Are halachos that were received at Sinai (or in the desert shortly after) but not recorded in Tanach--such as the method for kosher slaughter alluded to in Deuteronomy 12:21--considered rabbinical or biblical laws? I ask because, if rabbinical, they would seem to be of a higher status than many other forms of rabbinical law (g'zeiras, takanas, derashah, etc.) insofar as they were given to Moshe Rabbeinu along with the written Torah.

If rabbinical, are these treated entirely as "regular" rabbinical laws--subject to the same norms of self-limitation as the others--or as in any way distinct or higher? (In what cases?) And why would the Oral Law be considered rabbinical if Halacha l'Moshe mi'Sinai is considered biblical?

Answer 1

A great question, which is treated in Rambam and Ramban around the Sefer Hamitsvot. Sefer Megilat Esther quoted Sefer Zohar Harakyia which explains the Rambam. We will try to explain Rambam's view. What is called Oral law? What is called rabbinical? Are there halachot entirely orally transmitted which are not rabbinical? Is there a hierarchy in rabbinical laws? In the __introduction to his commentary to Mishna__ . Rambam clarify all this

1. There are for some halachot written in Tora and their meaning is unanimously recognized thanks to oral transmission (e. g. concerning the 4 minim and lex talionis, shechita). The orally transmitted information is not rabbinical, that is, not discovered by chachamim. This is a first kind of oral law from Sinai considered deorayita. There's sometime a way to understand or deduct à postériori those halachot from the written Tora.

2. Some halachot are transmitted from Moshe from Sinai and have no scriptural allusion . They are called in Chazal "Halacha Lemoshe Misinai" . Ramban (root 2) disagreed with the fact that Rambam called them "from scribes words" and Zohar Harakyia answered that Rambam too considered those dinim as deorayta concerning safek as for shyurim (kazait, cabetsa... ) deorayta which are purely Halacha Lemoshe Misinai. The term divre sofrim is ambiguous and makes the Rambam hard to understand.

3. Some halachot are found through reflection and reasoning, often in verses, sometimes are very old, even from Moses himself and are called from scribes words (sefer Hamitsvot shoresh 2). When we say reasoning, this includes the use of thirteen midot to interpret Tora . When we look at the 13 midot, we separate two kinds of dinim learned from 13 midot. The first kind results from deduction without transmission. The second kind is transmitted. Chazal said that the last are Tora equivalents. Zohar Harakyia explains: The dinim from the second group are deorayta concerning rules as sfeka deorayta but Rambam called them derabanan to express that they cannot be counted in 613 M because they are stemming from roots which are the 613 M . For each item of this second group, Chazal said explicitly that this specific din is deorayta (for instance tum'at nivlat clean bird which Rambam called derabanan in intro to seder taharot, and pasked for it the same rules as deorayta, kiddushe kesef also are called by Rambam divre Sofrim but their din is din Tora in all aspects) .

Are halachos that were received at Sinai (or in the desert shortly after) but not recorded in Tanach--such as the method for kosher slaughter alluded to in Deuteronomy 12:21--considered rabbinical or biblical laws?

Not recorded but alluded are this kind and are divided in two subgroups as mentioned above. Rambam calls them divre Sofrim but those transmitted from Sinai have the same rules as Torah exactly.

There is no Machloket between Chachamim in the two first kinds. But in the third (for his first part ) there are often Machloktot.

4. The fourth kind of halachot are ordinances . There are rabbinical even if Moses decreed them.

5. The fifth are enactments which are innovations called takanot, and are also rabbinical.

   I ask because, if rabbinical, they would seem to be of a higher status than many other forms of rabbinical law (g'zeiras, takanas, derashah, etc.)

   Gzeras are the fourth kind and are rules with specific kulot of rabanan rules. Takanas are the fifth kind. They have also owns special rules.

   Higher status for second kind and second part of third kind.

   If rabbinical, are these treated entirely as "regular" rabbinical laws--subject to the same norms of self-limitation as the others--or as in any way distinct or higher? (In what cases?)

   Rabbinical is their name as explained Zohar Harakyia (Rabbi Shim'on ben Tsemach Duran) because they are transmitted by Chachamim without written (biblical support) but their status is deorayta.

   And why would the Oral Law be considered rabbinical if Halacha l'Moshe mi'Sinai is considered biblical?

   In Rambam terminology both are called derabanan and have orayta status.

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You can see the mefarshim on Sefer Hamitsvot. The discussions about the second root are a bit length and complex. I hope this helps. If somewhat is not clear I will try to improve it.

Answer 2

(I ran out of time to look up and provide sources beyond those for the central point. This answer is known to be incomplete. I am posting it now anyway with plans for further editing so that (1) I don't risk losing what I typed so far, and (2) I can crowdsource the job of finding those sources. So rather than downvote before those edits, how about contributing to the effort?)

As a prelude, we should clarify that there are actually two uses of the expression "halakhah leMoshe miSinai":

First, it is used literally. A law given to Moshe from Sinai. Sinai here is broad, meaning the wilderness, not the mountain. There is no guarantee that this particular detail was received during Moshe's 120 days atop the mountain.

Second, it is also used idiomatically, "as sure as if it were given to Moshe from Sinai". This idiom is used for laws that were known to be rabbinic enactments. It even later got used in Ashkenaz to refer to Nusach haTefillah -- traditional tunes used by chazanim.

I will limit this answer to the first, literal, usage.

What does it mean that the law is categorized deOraisa? The most notable pragmatic difference is that we err on the side of stringency when a doubt arises in a Torahitic law (safeiq deOraisa lechumera); while if the law were deemed rabbinic, we are permitted to be lenient in cases of doubt (safeiq derabbanan lequla).

Among other potential pragmatic differences is that one person can only fulfill an obligation on behalf of another if the person doing the action is equally obligated. A person who is only obligated deRabbanan could not fulfill an obligation for someone who is obligated deOraisa. But the issue of safeiq (doubt) makes an easier to find litmus test.

One last clarification before getting to actually answering. There is a middle ground between deOraisa and deRabbanan. Megillah reading for men was legislated by the Anshei Keneses haGedolah (the Great Assembly; the high court of the early 2nd Temple period), and therefore is not deOraisa. However, among the members of the legislating court were many prophets, so that the law had Hashem's imprompeteur. It is not just another rabbinic law. In contrast, it is rabbinic law that women hear megillah. For this reason, the aforementioned rule applies: because a woman is less obligated to hear megillah than a man, a man cannot fulfill his obligation by hearing a woman read. Some sources understand the term "divrei soferim" as referring to this middle ground -- prophet endorsed rabbinic law. After all, sages of this period are often called by the term "soferim", such as "Ezra haSofer".

So, after all that, I would reduce your question to: When a law is deemed halakhah leMoshe miSinai in the sense that Moshe actually was given the law by G-d, would doubts in that law be ruled stringently? If so, it would make sense to apply the term deOraisa. But if not, we would need to see if other bellwethers apply. If the results are mixed, perhaps halakhos leMoshe miSinai also sit in the middle ground.

Measures (shiurim) are halakhos leMoshe miSinai (Yerushalmi Pei'ah 1:1, Bavli Sukkah 5b, Yuma 80a). But when measuring something for the sake of a mitzvah deOraisa, we rule stringently. (Rav Avohu on Niddah 58b, and invoked by Tosafos, Berakhos 26b). We do not consider having the necessary size / weight / duration a rabbinic amendment to the original deOraisa law.

So it would seem that from a pragmatic point of view, the answer to your question would be that they are deOraisa.