Who knows thirty-one?

Please cite/link your sources, if possible. After about one business day, I will:

  • Upvote all interesting answers.

  • Accept the best answer.

  • Go on to the next number.

  • Should this be "Echad Ushloshim" or "Echad Usheloshim"? In other words, how should I transliterate the shva merachef?
    – Isaac Moses
    May 5, 2010 at 16:01
  • I like it the current way.
    – Shalom
    May 5, 2010 at 18:47
  • It depends if you go by the Radak or the Gra.
    – Yahu
    May 5, 2010 at 20:09
  • Yeah, I'm a Litvak.
    – Shalom
    May 5, 2010 at 20:22
  • Then it should be Usheloshim!
    – Yahu
    May 5, 2010 at 20:48

5 Answers 5


31 are the Canaanite kings whom the Jewish People defeated and killed. (Joshua 12:7-23)


31 is the gematria of "ויהי", "and it was ...". Two of the five Megilot (Esther and Ruth) begin with this word; the other three (Song of Songs, Ecclesiastes, Lamentations) don't contain it at all.

Chazal says "ויהי" indicates bad news. An explanation I'd heard was that this word is made of יהי, "will be" in the future, then reversed to the past with the "vav ha-hipuch." If we're taking our future and just forcing it to be just like the past, that's a very bad sign.

(Conversely והיה -- learning from our past and applying it to our future -- is a good sign.)

I think this is from R' Sorotzkin, though I could be mistaken.

  • Interesting vort!
    – Alex
    May 5, 2010 at 19:11
  • Checkmark for interesting vort.
    – Isaac Moses
    May 6, 2010 at 15:34
  • megillah 10b is the source
    – Kfir
    Jul 10, 2020 at 18:12

31 are the pages in Maseches Megillah (starts on 2, goes to 32)


31 is the most English dates possible in a Hebrew month. i.e., if the molad was at 1pm on Jan 1, the next molad would be around 1:44am on Jan 31.

(on a related note, 3 is the most Hebrew months in an English month, and 3 is the most English months in a Hebrew month; in the example above, Kislev, Tevet, and Shevat all fall out in Jan, while Jan, Feb, and March all overlap with Shevat)

  • 1
    The molads don't demarcate the change in Jewish months; Rosh Chodesh does.
    – Isaac Moses
    May 5, 2010 at 16:24
  • Ein hachi nami. it still works :p
    – Jeremy
    May 5, 2010 at 18:24
  • 1
    It works more trivially with respect to R"Ch. Every long Jewish month is going to touch 31 civil days because it lasts 30 whole days, and the dividing lines are guaranteed to not coincide (nightfall vs. midnight).
    – Isaac Moses
    May 5, 2010 at 19:14
  • 1
    Actually, come to think of it, that guarantee doesn't hold near the poles. If a Summer Rosh Chodesh for a 30-day month happens to fall, somewhere in the extreme North, on a day when nightfall is before midnight, and if by the following Rosh Chodesh, nightfall has moved to after midnight, then your Jewish month has contact with 32 civil days! Note that this works whether you use sunset or your favorite value for Tzeit (though you don't have to go as far north for the latter).
    – Isaac Moses
    May 5, 2010 at 20:00
  • 32: judaism.stackexchange.com/a/1412
    – Isaac Moses
    Jul 22, 2016 at 14:07

Thirty-one is no. (Gematria of "lo")

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