Hilchos Niddah Siman 189, Seiimf 2-3

Siman 189 Seifim 2 - 3

2. How is a cycle established? If she has 4 periods with 3 equal intervals between them. For example, if she sees today and then after another 20 days, then after another 20 days and then after another 20 days she has established a vesses kavua that is a vesses haflaga. Therefore, she requires 4 periods, since the first one is not relevant since it was not the endpoint of an interval. Even after the first interval of 20 days, we will suspect the 20th day following. Similar rules follow for the day of the month - if she saw, for example, on the 21st or 25th of a specific month, we are concerned with the 21st or 25th day of the following month and relations are prohibited for the entire onah. This is the rule for all other types of vestos - she must suspect them except for the vesses hadilug - the skipping pattern that will be discussed later on. The only reason why we require 3 times to establish a pattern is for the purpose of subsequent uprooting of the pattern, so that something that was established as a result of 3 repetitive patterns can only be uprooted by 3 consecutive failures of the pattern. So long as it has not been uprooted, she must still be concerned for that pattern. However, to prohibit a woman one occurrence is adequate. However, in that case something that is suspected as a result of one instance of the pattern is uprooted by a single failure of the pattern. This is true even if the pattern was repeated twice and the third time it was not, she need not be concerned with it any longer.

3. If she established a vesses for hours and not for days, she only suspects her hour. This vesses is uprooted with one off-cycle period even if the woman did not perform a self-examination.

What's Going On?

This is the beginning of a very complicated set of laws about determining the onas vesses. The basic rule for establishing a vesses kavua is that the pattern that establishes it recurs 3 times. Therefore a vesses kavua is established if a woman has the beginning of a period every 28 days, for example. If she were to see on the 1st of Nisan, the 28th of Nisan, the 25th of Iyar and the 23 of Sivan - she will have established a cycle of 28 days and will follow the rules associated with a vesses kavua. There is no way to establish a vesses haflaga in fewer than 4 periods, since we are measuring the intervals between them. The counting is without regard to the length of the actual bleeding and is based only on the start date.[1]

If a period begins on the same day of the Jewish calendar month 3 times in a row, the woman establishes a vesses kavua of a vesses hachodesh type. Establishing this kind of cycle requires only 3 periods, since in this case we are not measuring intervals as in the haflaga but rather we are evaluating absolute dates. One who wishes to observe properly the laws of vestos should record the details of menstruation on a calendar, including the onah of the flow.[2] Alternatively, one can use the vesses calculator that is included in the download section of this website. Those who have a custom to observe the Onas Ohr Zarua should apply it to a vesses she-aino kavua[3].

The vesses HaChodesh will sometimes be 30 days and sometimes 31, depending on whether the month has 29 or 30 days[4].

Regarding the Vesses HaShaos, there is a dispute about whether she is prohibited every day of the month during that hour or if her onah of separation is limited to the single hour. The dispute, then, is whether a Vesses HaShaos is a strictness or a leniency. The Halacha concludes that the Vesses HaShaos is a leniency; in practice today we do not permit its use.

Following are two simple examples of the times a woman needs to separate from her husband from her first vesses, ultimately establishing a Vesses Hafloga, or as in the second example, a Vesses HaChodesh. Remember that the woman who do not have a vesses kavua need to separate from their husbands on each of the 3 different days defined by the beinonis period, the date of the month and the length of the previous cycle.

Case #1 – Woman ultimately establishes a Vesses Haflaga

Period #1	Method	# of Days	Vesses Date	Period #2	# of Days	Vesses Date	Period #3	# of Days	Vesses Date	Period #4
3 Adar I	Beinonis	30	2 Adar II	3 Adar II	30	3 Nisan	4 Nisan	30	3 Iyar	4 Iyar
	Haflaga	*	*		31	4 Nisan		31	4 Iyar
	HaChodesh		3 Adar II			3 Nisan			3 Iyar

The woman has had 4 periods, each one separated by 31 days from the previous. The woman now has a vesses kavua and will only need to separate on 5 Sivan, which is 31 days after her 4^th period.

Case #2 – Woman ultimately establishes a Vesses HaChodesh:

Period #1	Method	# of Days	Vesses Date	Period #2	# of Days	Vesses Date	Period #3	# of Days	Vesses Date	Period #4
3 Adar I	Beinonis	30	2 Adar II	3 Adar II	30	3 Nisan	3 Nisan	**	**	3 Iyar
	Haflaga	*	*		31	4 Nisan		**	**
	HaChodesh		3 Adar II			3 Nisan			3 Iyar

By the 3^rd period on 3 Nisan, the woman will have now experienced menstruation on the 3^rd of 3 consecutive months. In anticipating period #4, she considers only the date of the month and does not worry about either the haflaga or the beinonis.

* - there is no haflaga after only one cycle, as explained above.
** - irrelevant, since the woman has now established a Vesses HaChodesh.

Back to Summary
Back one page
Forward one page
Have a question?

Last Revised December 23, 2004

[3] SSH 189:2(3), although many others are lenient

[4] A month of 29 days is called chaser and one of 30 days malai. The Jewish year is comprised as follows:

Nisan – 30	Av – 30	Kislev – 29 or 30	Leap year:
Iyar – 29	Elul – 29	Teves – 29	Adar I – 30
Sivan – 30	Tishrei – 30	Shvat – 30	Adar II – 29
Tamuz - 29	Cheshvan – 29 or 30	Adar – 29