Coming off the recent question of complex וסתות, what about a pattern of 27,29,30; 28,29,27; 31,29,30?

In this case there is a pattern for every middle one while the rest remain random. Are we קובע a חזקה interspersed with non-מוחזק data?

On the one hand we can equate this to the ox that gores every third person. In that case the people he skips would usually tell us that he doesn't gore, but we look past that and count the pattern. Here too, ignore the random and count the pattern.

On the other hand, in the case of the ox we have a quantified pattern, and here we don't. Any sources or solid arguments are appreciated.

1 Answer 1


Yes, there are examples of such vessts.

Shulchan Aruch Y.D. 189:6 has the halacha of vesst yom hachodesh. The case is that a woman establishes a vesst of having her period on Rosh Chodesh for 3 consecutive Roshei Chodashim. Badei Hashulchan #51, citing "poskim," writes that even if she has other periods in between these Roshei Chodashim, she still establishes a vesst for Rosh Chodesh. He writes the same in 189:9 #70 regarding a vesst pattern of alternating Rosh Chodesh periods.

This assumption is actually explicit in both the Gemara and the Shulchan Aruch. Niddah 39b has the case of a woman who has her period on Rosh Chodesh of month one, Rosh Chodesh of month two, day 25 of month two, and then Rosh Chodesh of month three, in which case she still establishes a pattern for Rosh Chodesh, despite the interrupting data of day 25 of month two. In the Shulchan Aruch, Y.D. 189:32 is the case of establishing a vesst concurrent with an existing vesst, i.e. having established a pattern of Rosh Chodesh, and then establishing an additional pattern for day 20 of the month, despite the Rosh Chodesh pattern continuing.

More than this, there is the case of the Darkei Moshe 189:1 in which he discusses the case of a woman who has periods on Rosh Chodesh Nissan, 2 Iyar, Rosh Chodesh Sivan and 4 Sivan, Rosh Chodesh Tamuz and 5 Tamuz (following a pattern of intervals of 31 days if you discount the interrupting Rosh Chodesh Sivan and Tamuz periods). Here, the Rema is going so far as to discount the periods which are inconsistant with the intervals to not even consider them as splitting the interval itself!

The Rema Y.D. 189:13 applies the same principle in his case of a woman who has periods on Rosh Chodesh Nissan, 20th of Nissan, and Rosh Chodesh Iyar, and he writes that she needs to treat the 9th of Iyar as a day of possible vesst due to the haflaga of Rosh Chodesh Nissan to the 20th of Nissan despite the interrupting period on Rosh Chodesh Iyar.

Note that the Rema is using this principle even for הפלגות, not just for יום החדש.

  • So if in her whole life she has her period on Rosh Chodesh three times, that establishes a chazaka? I don't understand how that works.
    – Daniel
    Jun 9, 2015 at 20:28
  • @Daniel no, it has to be at consistent intervals. Consecutive, or every other, or every 3rd... Jun 9, 2015 at 20:47
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    He said the same about a recurring cycle - i.e. hypothetically a pattern of 28;31;24;26;32;27;31 which then repeated 3 times as 28;31;24;26;32;27;31;28;31;24;26;32;27;31;28;31;24;26;32;27;31 would make a vesst kavua of that base pattern. But again, one is not required to keep track due to its unlikelihood. Jun 9, 2015 at 20:50
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    What would it take to undo that kind of kavua, three months or three entire patterns?
    – HaLeiVi
    Jun 9, 2015 at 22:58
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    @HaLeiVi It's a good question (+1!). In a more simple case which follows the same principle (Rabbeinu Chananel's case of 15;16;17;15;16;17;15;16;17), the Shaarei Tohar says you need to undo each day independently, although they do not need to all be undone at once (i.e. each day is looked at as its own pattern). Lechem V'Simla is mesupak about it though. I assume the same would extend to this case. Jun 10, 2015 at 3:19

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