The Talmud says:

Mishnah: A Nazirite vow of unspecified duration [remains in force] thirty days. Gemara: From where is this rule derived? Rabbi Mattena said: The text reads: He shall be [yihyeh] holy, and the numerical value of the word "yihyeh" is thirty. [Nazir 5a]

I thought we were not allowed to derive halacha from gematria. Are we?

(As an aside, wouldn't the gematria of "holy" be more appropriate?)

  • 2
    – Double AA
    Commented Oct 31, 2018 at 15:34
  • @DoubleAA -- Yes, There are other examples. But I am looking for a statement, "No, we may not derive halacha from gematria". (Gematria is only a mnemonic device.) Is there such a thing? Commented Oct 31, 2018 at 16:28
  • Consider judaism.stackexchange.com/q/44758/759
    – Double AA
    Commented Oct 31, 2018 at 16:31
  • @DoubleAA -- Is there a statement anywhere that an asmakhta is a known and applied oral law from long, long ago, but whose derivation from Torah has been lost, so the gematria is used just as a mnemonic, not a proof? Commented Oct 31, 2018 at 16:40

2 Answers 2


Your motivating example is not necessarily a case of “deriving” halachah from gematria.

Rambam writes in is Commentary to Nazir 1:3 that the thirty-day nazir rule is a received tradition, which the Rabbis supported using the gematria as a hint.

I speculate that Rambam says this as he is loathe to view a gematria as the primary source for this halachah. This would suggest that he is of the opinion that one cannot straightforwardly derive laws from gematria.

  • 1
    I'm not sure this answers the question
    – Double AA
    Commented Oct 31, 2018 at 16:31
  • Edited to more directly answer the question. (Admittedly it’s now somewhat more speculative...)
    – Joel K
    Commented Oct 31, 2018 at 16:36

Halachah is ruled, not necessarily derived. It can be ruled in two ways:

  • either by learning the source and deriving from it, as you mentioned,

  • or by ruling it first and making an Asmachtah afterward (by relying on a verse).

This is very common with the Gemmarah and it is impossible to distinguish between them. I posted a question about this problem.

Your question is a good example of an Asmachtah for a Halachah - something that merely strengthens the claim.

  • Isn’t an asmachta usually a din derabbanan backed up with a hint from a pasuk? I’m pretty sure this is deoraita...
    – Joel K
    Commented Oct 31, 2018 at 15:45
  • @JoelK As we have no tools for judging a Halachah objectively, "anything goes" - whatever sounds reasonable proves your point. That's called אסמכתא.
    – Al Berko
    Commented Oct 31, 2018 at 15:48
  • @Al Berko -- OK, so it's an asmakhtah, but ARE we allowed to learn halacha from gematria? Any sources that directly address this question? Commented Oct 31, 2018 at 16:12
  • There are no rules of how to rule Halochos. Our motto is כל דאלים גבר - everything goes. He can say "Cause I said so" - won't it suffice? BTW a sage does not have to give you his reasoning at all, maybe you won't understand, maybe you'll misunderstand and think it's BS. Sometimes he feels it's true but can't find a good supporting claim.
    – Al Berko
    Commented Oct 31, 2018 at 16:16
  • 3
    @AlBerko The quote is יבקשו תורה מפיהו, not שמע בקולו. You have to seek torah from him. Pronouncements ex cathedra are part of another religion.
    – Joel K
    Commented Oct 31, 2018 at 17:05

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