This question asks why the flood didn't end on the 18th of Cheshvan (one year after the start). My question is more basic: why does the torah give us precise dates here at all? Bereishit 7:11 tells us it began on the 17th of the second month and Bereishit 8:14 tells us it ended on the 27th of the second month a year later -- but I don't think we get another precise date before the exodus begins. (One can of course question which month is meant by the second month -- the other question assumes Cheshvan -- but regardless of which it is, the torah identifies a specific month and specific dates.)

Why is it important to tell us the flood began and ended on these exact dates?

  • To tell us it was a complete solar year? – Menachem Oct 31 '13 at 5:07
  • similar judaism.stackexchange.com/q/17810/759 – Double AA Oct 31 '13 at 6:50
  • @Menachem, we get durations without dates all over the place; we know how old people were, that Avraham circumcised Yitzchak on the 8th day, how long the famine in Mitzrayim was... the text is clearly able to tell us about durations without giving us exact dates. So why the exact dates here? – Monica Cellio Oct 31 '13 at 12:38

Ralbag in his commentary to the Flood Narrative writes as follows:

והנה השלים זה הסיפור והפליג להאריך בו לרוב התועלת המגיע ממנו ולזה דקדק במספר הימים אשר ירד הגשם בלי הפסק ובשאר הפרטים לישב יותר בלבנו אמיתת זה הסיפור כי כבר נאמין יותר בספורים כשיסופר מענינם פרטים רבים

And behold it completed this narrative and elaborated on it extensively due to the abundance of benefit that comes from it. And for this it was precise in the number of days that the rain fell nonstop, and in the other details, in order to settle more in our hearts the truth of this narrative. For we believe more in narratives when many of their details are told.

More generally, he writes a bit earlier:

עם שזה דרך התורה לזכור קצת הפרטים ולעזוב קצת

It is the way of the Torah to mention some of the details and to leave out some of them.

(You can see my answers here and here for some of Ralbag's comments about the Torah's general brevity and redundancy.)

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  • You have a special gift of finding the exact source that speaks about the subject. The problem, however, with most of those sources, they are short-sighted, they only explain one phenomenon completely neglecting the rest of the Torah. Bereyshis is full of stories but none mentioned exact dates. – Al Berko Oct 13 '18 at 21:07
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    @AlBerko I guess I’ll take that as a compliment? – Alex Oct 13 '18 at 23:29

See Rashi on chapter 8 verse 4 where he deduces based on the dates given how submerged in the water the Teiva was - 11 cubits. An interesting point from which we can derive with a bit of calculation and Archimedes' priniciple, a possibly even more fascinating point: that it weighed around 15,645 metric tonnes (based on Rabbi Hadar Margolin's proposition that the Ama was 46.5 cm - ספר הידורי המידות).

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The seventeenth day (7:11) comes seven days after the warning received a few verses earlier (7:4 and 7:10), which means that the warning itself came on the tenth day of the second month, which is the fortieth day of the year, yielding an intriguing symmetrical structure :

  • forty days from Rosh ha Shanah until the warning,

  • then a full week between the warning and the beginning of Noah's Flood,

  • followed by forty days of heavy rains and massive inundations,

mounting up to a total of eighty-seven days, about the length of a season, spanning roughly from the autumn equinox to the winter solstice.

The forty-day periods are ultimately of Egyptian origin (50:3), since they divided their years (which, just like Noah's Flood, started in autumn, with the flooding of the Nile) into twelve months of thirty days each (7:24 and 8:3), the months being further subdivided into three decans, having ten days each.

However, the middle time-period, instead of spanning for a full Egyptian decan, is instead three days shorter, having the same length as a Babylonian week1, with whose lunar calendar the ancient Hebrews were also intimately acquainted, eventually adopting it as their own. Now, these three days reduce what would otherwise amount to a ninety-day period to one of only eighty-seven, a number which can only be written as the triple of twenty-nine, hinting at the astronomical knowledge that the duration of a synodic month lies somewhere between the two values, being perfectly equal to neither.

Between these two different calendars, Egyptian and Baylonian, there is a difference of about ten days, representing the inequality between the solar and lunar years (7:11 and 8:14).

1 Come to think of it, the time span from Passover to Pentecost seems itself based on an attempt at equating five Egyptian decans by seven Babylonian weeks.


A book written by a human claiming to be divine will not include dates (or any specific details) lest someone spot an error in them and then claim that it is not divine. The Torah being divine is not afraid to include specific details; thus this proves that the Torah is a Divine Document.

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