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

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

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 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 make 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 afford the 13 midot, we separate here two kinds of dinim learned from 13 midot. The first results from deduction without transmission. The second is transmitted. Chazal said that they 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 din is deorayta (for instance tum'at nivlat clean bird which Rambam called derabanan in intro to seder taharot, and paskedthis rule as deorayta, kiddushe kesef also are called by Rambam divre Sofrim but their din is din Tora in each detail ) .

   
   

   
   

   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. Rambam calls them divre Sofrim but those transmitted from Sinai have the same rules than 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 az 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.