1. What is the definition of kalus rosh?

  2. What are the halachos of kalus rosh and where do they apply?


2 Answers 2


Shulchan Aruch (OC 151:1) lists three examples of kalus rosh, though doesn't define it explicitly:

בתי כנסיות ובתי מדרשות אין נוהגין בהם קלות ראש כגון שחוק והתול ושיחה בטילה

We don't practice kalus rosh, like mirth, jest, and wasteful conversation, in synagogues and study halls.

Mishna B'rura ad loc. clarifies "wasteful conversation":

That is: Even secular conversation for the purpose of sustenance — which is permitted outside — is forbidden in the synagogue, and specifically completely wasteful conversation, from which it is seemly to always refrain, and of which sin the Zohar (Vayakhel) greatly amplified the significance.

  • "wasteful" doesn't seem like a good translation. Something which is productive, permitted and obligatory to do isn't "wasteful" even if this building is not the right context to have it in.
    – Double AA
    Jul 30, 2014 at 0:01
  • @DoubleAA בָּטֵל means "wasteful", or something very similar. I guess the ambiguity in that word is part of what made MB define it for us. Or maybe not. In any event, I quoted the MB in the answer, so, even if my translation is poor, no harm done.
    – msh210
    Jul 30, 2014 at 4:44
  • many synagogues are built with conditions so that they can eat and speak in it
    – ray
    Aug 6, 2015 at 20:50

To make light of something important. See Rashi on the bottom of Megila28a. Kallus means that you make light of them. I am assuming he is learning the word 'rosh' is referring to the batei kneisios the gemara is discussing, with rosh meaning something important. Apparently it does not mean to be light headed!

  • Is it not that becouse you are in a state of kalos you make light?
    – hazoriz
    Aug 6, 2015 at 9:29
  • Words of rashi אין אוכלין בהן כו'. ולא גרסינן ואין אוכלין בהן דכולהו פירושא דקלות ראש הן לשון קלות שמקילין אותה:
    – hazoriz
    Aug 6, 2015 at 9:38
  • @hazoriz It seems from the last two words of Rashi that it is an active making light of the objects under discussion.
    – user6591
    Aug 6, 2015 at 11:15

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