Rosh Chodesh is 2 days as today is the 30th of Shevat. Adar doesn't actually begin until tonight. Yet the sense of mishenichnas Adar marbim b'simcha seems to hold sway even today, and not just in the additional simcha of Rosh Chodesh.

The most local proof to this is the local policy on Purim Torah, which only mentions "Rosh Chodesh" and not "The beginning of Adar" but other sites seem to bring in the idea of Adar before the month. On an old thread on the Yeshiva World, I found this statement: "Even though it's really 30 shvat, it's still called rosh chodesh adar." But the Chabad website has its mention of Mishenichnas only on the entry for the second day. So I don't think this is a meta-question.

Is it halachically the case that on a 2 day Rosh Chodesh, the upcoming month is considered as if it has begun even on the first day?

2 Answers 2


Is it halachically the case that on a 2 day Rosh Chodesh, the upcoming month is considered as if it has begun even on the first day?

The basic answer is yes, unless specific language is given to differentiate. Thus if one says the start of Adar or Rosh Chodesh Adar, the the first day of Rosh Chodesh is meant. If one explicitly says the first of Adar then the second day of Rosh Chodesh is meant.

As an example, the Rambam says that if someone makes a neder for "this month", the thirtieth day of the month (first day of Rosh Chodesh) is treated as the next month and the neder has expired. Thus we see that when someone speaks of "Rosh Chodesh" for halachic purposes, then we use the first day of Rosh Chodesh as beginning the month based on the principle that the Torah speaks Belashon Adam under normal circumstances

Rambam Nedarim - Chapter 10

Halacha 3

שאני שותה חדש זה אסור בשאר ימי החדש אבל ביום ראש חודש יהיה מותר אף על פי שהיה חדש חסר שאני טועם חדש אחד אסור שלשים יום גמורים מעת לעת נדר חדש סתם אסור שלשים יום מעת לעת מספק:

[When one takes a vow, saying:] "I will not drink [wine] during this month," he is forbidden in the remaining days of the month. He is, however, permitted on the day of the following Rosh Chodesh even if the month is lacking.8 [If he took a vow, saying]: "I will not drink [wine] for an entire month," he is forbidden for 30 full days. [If he said]: I will not drink [wine] for a month," he is forbidden for 30 full days because of the unresolved question.9

As explained

Footnote 8

A month which is lacking is a month of 29 days [as opposed to a month of 30 days; see Hilchot Kiddush HaChodesh, chs. 1-3, which discusses the principles determining when a month is given only 29 days and when it is given 30].

The commentaries question why the Rambam (based on Nedarim 60b) speaks of the month being lacking. Seemingly, it is quite obvious that if there are only 29 days in a month, one would be permitted on Rosh Chodesh in the next month. The new month has already begun. A point that has to be made is that even if there are 30 days in a month, one is permitted to partake of wine on the thirtieth day. Since it is Rosh Chodesh of the coming month, the vow has concluded even though the date is the thirtieth of the previous month.

The Radbaz explains that this in fact is the Rambam's intent, even though his wording is somewhat difficult to explain in that manner. This interpretation is reflected in the wording of the Shulchan Aruch (Yoreh De'ah 220:4). The Or Sameach offers a different interpretation, stating that when a month has only 29 days, sometimes the conjunction of the sun and the moon does not take place until the first day of the new month. Even so, since it is already Rosh Chodesh, the vow is concluded.

  • What if the wording of the neder was "I will not drink wine in the month of Shevat"? In this case are talking about the named month, not the idea that "whole month" is 30 days and "this month" is 29.
    – rosends
    Feb 26, 2017 at 15:55
  • @Danno That is why the Rambam says "a month" meaning starting today a month, which goes for 30 days from the time the neder was made. A named month would be from Rosh Chodesh of that month until (and not including) the Rosh Chodesh of the next month. A named month is like saying "this month". Feb 26, 2017 at 16:00
  • So naming Shevat in the neder would allow someone to drink when it is still Shevat? But saying "a whole month" (not naming) on the first of Shevat would stop someone from drinking until the 30th day is over?
    – rosends
    Feb 26, 2017 at 16:03
  • Who says that any of this is even relevant to the question at hand? That is, who says that the idea of celebrating in Adar is subject to these technical discussions?
    – mevaqesh
    Feb 26, 2017 at 16:50
  • @mevaqesh, the asker does, in his last sentence. Personally, I don't think that sentence belongs there. But it's there.
    – msh210
    Feb 26, 2017 at 17:22

It appears that this isn't an actual technical rule, and therefore does not have technical parameters. (perhaps this is part of the reason that Rambam, Tur, and the Shulhan Arukh don't mention this "rule").

Rather, the idea of increasing joy in Adar seems to be as the Meiri (Ta'anit 27b) writes, that:

ובגמרא פירשו שכמו שמשנכנס אב ממעטים בשמחה כך משנכנס אדר מרבין בשמחה הכל הערה שראוי להתפלל ולהודות לאל בכל עת ובכל זמן כפי הנאות למה שאירע באותו זמן

That is, this statement is meant to inspire us to pray and praise God all the time, as is appropriate for what occurred then.

If, indeed, this isn't a technical halakhic rule, but rather an encouragement to not miss an opportunity to capitalise on a moment in time and channel it into service of God, then the question doesn't really start. If people are already excited, then that makes it an appropriate time to channel that into service of God. (See Kuzari II:50) for more on the idea of joy being a form of divine service when it is part of a deliberate experience, rather than mere unbound wildness).


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