When I read in the Talmud, Shulchan Aruch, etc. that a halacha is halacha leMoshe Misinai (a law given to Moses at Mt. Sinai), I compare it to a "postulate". It seems like a statement or rule that we accept and follow and we can't find a Torah source explaining why we do it.

How do we actually know that this is really in this category and not just a minhag that was adapted by a group of people at some point but we also don't know its source?

And if it is halacha Lemoshe Misinai, how do we know that we are doing it correctly as it was initially relayed to Moshe? Maybe after so many millennia someone relayed it incorrectly and we really don't know?

  • 2
    Can't you ask these same questions about any other halakhic category?
    – Double AA
    Oct 30, 2019 at 15:17
  • 2
    There are only 31 such Halochos (out of thousands we now have) - not a big deal. See judaism.stackexchange.com/a/86862/15579
    – Al Berko
    Oct 30, 2019 at 21:24
  • Fascinating, but who really cares? It's kinda joker used to silence a meaningful discussion but practically it makes no difference. I think this is the reason that HL"M is still told in the name of Rabbis. If it really was HL"M, there was no need to mention who said that because everyone should have known it.
    – Al Berko
    Nov 27, 2019 at 16:58
  • I suspect that the scarcity of those Halochos proves that those were mere excuses, it's highly implausible that G-d writes everything in the Torah, but 31 unrelated Halochos.
    – Al Berko
    Nov 27, 2019 at 17:03

3 Answers 3


The Yerushalmi in Peah (Chapter 2 halacha 4):

אמר ר"ז בשם ר' יוחנן אם באת הלכה תחת ידיך ואין אתה יודע מה טיבה אל תפליגנה לד"א שהרי כמה הלכות נאמרו למשה בסיני וכולהן משוקעות במשנה אמר ר' אבין ויאות היא שני מיני חטים אילולי שבא נחום ופי' לנו יודעין היינו

Rebbi Zeirah says in the name of Rebbi Yochanan: If a halacha (mishnah or berriasa) comes to your hand and you don't know its status (source), do not reject it, for many halachos where said to Moshe on Sini, and all of them are embedded in the Mishnah. Rebbi Avin says: Really, the ruling of "two types of wheat", if Nachum had not come to explain to us (that it is a Halach LeMoshe MiSini, in the Mishnah here), would we have known?

This seems to take the opposite approach from the OP. We assume that an accepted tradition is valid because we suspect that it might be a Halacha LeMoshe MiSini. We will only call it that when we have an explicit tradition saying so.


The phrase אמר רבי אליעזר כל מקום ששנינו באמת הלכה למשה מסיני is found several times throughout the Talmud Yerushalmi. The simple meaning is that the Teachers use the words ‘in Truth’ to keep track of which laws originate with Moshe. Therefore, the usage of באמת as a signifier of such is very much included in all oral tradition extant, and can only be equally considered by one as any other aspect.

See practical application and discussion of this principal in Rosh, Mikvaos 1.

See further discourse regarding these differences in Mahratz Chayus, Mevo Hatalmud 15.


I believe that it is exactly as you say: halacha Lemoshe Misinai is any halacha which we do not know its origin; but we trust that the Rabbis' tradition is faithful to the teaching of Moshe.

We are not afraid of "mistakes" since the tradition of Israel (with the rulings of the authorized Rabbis) is the true halacha Lemoshe Misinai.

IMHO this is one of the ideas in the midrash on Moshe and Rabbi Akiva (Bavli Menachot 29b). This idea is also expressed by Rabbi Yehuda Halevi in Kuzari part 3:41.

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