purim katan

The Mishna (Meg 6) writes that if the megillah was read in Adar Rishon, it must be re-read in Adar Sheni or you are not yotzei. The Mishna continues that the only difference between Adar I and Adar II is with respect to megillah reading and matanos la'evyonim.

The gemara is medayek from the Mishna that with respect to hesped and ta'anis the two Adars are equivalent -- just like on Purim of Adar II one cannot fast or give a hesped, so too one cannot fast or give a hesped on the same date in Adar I.

This is the source for what we call Purim Katan. It's not a day of full celebration, but it's not an ordinary weekday either.

The Rosh, however, learns a completely different pshat in the Mishna. The Mishna is not two separate statements, but rather is one halacha: in a case where megillah was read in Adar Rishon, and then **afterwards** beis din declares a leap year, the only difference between the two Adars will be that the megillah must be re-read and matanos la'evyonim given again in Adar II.  However, if beis din declared it a leap year sometime before 14 Adar I and everyone knew not to read megillah in Adar I, there would be no issur hesped or taanis on 14 Adar I either -- the month, writes the Rosh, would be no different than Shevat.

B'pashtus the machlokes Rishonim here boils down to how to understand the concept of adding an extra month to the year. According to the Rambam and RIF, a leap year means there are 2 Adars, and therefore there should in theory be 2 Purims.  In practice, the gemara darshens from pesukim that the megillah need only be read in Adar II. According to the Rosh, even in a leap year there is only one Adar and only one Purim. The month we add could just as well be called Shevat II, or "Extra Month."  It is Adar in name only, but carries none of the character or significance of the true Adar, Adar II.  

How do we celebrate Purim Katan?  Ran writes that the issur hesped and taanis is a symptom of an underlying chiyuv of simcha; therefore one should have some sort of festive meal.   Tosfos disagrees. S.A. paskens like Tos; the Rama quotes the Ran's view.

Chasam Sofer has an amazing chiddush that Purim Katan may be even more significant that the real Purim.  The gemara darshens a kal v'chomer: if we say hallal on Pesach when we were freed from bondage, then certainly we should say hallel when our lives have been spared such as occurred on Purim.  (Kri'as ha'megillah is a kiyum of hallel.)  A kal v'chomer is one of the 13 midos the Torah is darshened by, and anything learned through the 13 midos has the status of a din d'oraysa. Therefore, says Chasam Sofer, exactly what to do to commemorate the nes -- reading megillah, seudah, etc. -- may be derabbanan, but the obligation to do so in some way is d'oraysa.     

Based on this logic, since since Adar I has the status of Adar (according to most Rishonim, not like the Rosh), the celebration of Purim Katan, marking the nes of Purim, is a chiyuv d'oraysa.   Zerizim makdimim -- why wait for Adar II when you have the chance to mark the miracle already in Adar I!  Chazal tell us for various reasons to defer reading megillah and matanos la'evyoniom until Adar II, but when we fulfill those mitzvos derabbanan should not impact out obligation to fulfill the mitzvah d'oraysa of remembering the nes in Adar I.