משנכנס אדר מרבין בשמחה

DAF HASHAVUA

TA’ANIS 29a                                

In many Shuls and homes, משנכנס אדר מרבין בשמחה signs are hung up, in the month of Adar.

This statement is  Halachically incorrect*. 

The Gemoro (Ta’anis 29a ) In the name of Rav it was said, "the same way, when the month of Av comes in you reduce with Simcha, so too when the month of Adar comes in you add with Simcha".

The Rambam and Sh. Aruch bring the Halacha of M'shenichnas Av Mema'atin B'simcha.

They do not** mention M'shenichnas Adar Marbin B'simcha.

The obvious reason is, there is no such  Halacha to be Marbeh B’simcha when Adar comes in.

The Chasam Sofer (O.Ch 160) explains:

Since  we don't Pasken like Rav that Aveilas starts on Rosh Chodesh Av,(According to halacha it starts onon Erev T.B.***), therefore we also don't Pasken that Simcha starts on Rosh Chodesh Adar.

The Halacha in Shulchan. Aruch & Rambam of Mishenichnas AvMematin B’simcha applies to only one thing ,not to build a Binyan Shel Simcha. All other types of refraining Simchas

eating meat , drinking wine etc. start only on Erev Tisha Baav

On this halacha we can't say The same as when Av comes in you are not allowed to build Binyan Shel Simcha-- so too when  Adar comes in you may build a Binyan

Shel Simcha. You may build a binyan all year round not only in Adar.

* According to the Shulchan Aruch & Rambam

** The Magen Avraham does mention it

***3 weeks, 9 days & Shavua Shechal Bo are Minhag.