When Tisha B'av begins after Shabbat, as it does this year, we begin fasting after sundown before Shabbat is over.

On the one hand, we postponed the full fast day of Tish'a B'av to Sunday, because you shouldn't fast on Shabbat. Yet, we're fasting while it is still Shabbat. Is this not a contradiction? Does beginning the fast during Shabbat not violate the concept of oneg Shabbat? Why is the fast allowed to begin before Shabbat is over?

  • 4
    Do you never go an hour on shabbat without eating
    – Double AA
    Jul 22, 2016 at 21:39
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    @DoubleAA I think there's a difference between not eating and fasting -- one is passive (i'm not eating at this moment), one is active (i'm not allowed to eat right now).
    – Scimonster
    Jul 23, 2016 at 19:15
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    @Scimonster "i'm not allowed to eat right now" is a prohibition, it's not an action. In any event all the issues of mourning on Shabbat are merely about appearances anyway (Tzina vs Parhesia)
    – Double AA
    Jul 24, 2016 at 3:55
  • You're supposed to eat three meals on Shabbat and you're supposed to eat before midday on Shabbat. Both of these would be problematic if you were fasting the entire day but not if you're only fasting for an hour at the end of the day.
    – Daniel
    Jul 24, 2016 at 14:21
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    See sefaria.org/Eruvin.40b.64?lang=en&with=all&lang2=en and the rest of the page/next page Jul 25, 2016 at 5:47

1 Answer 1


Not eating for less than an hour is not called fasting. Other prohibitions that would contradict Shabbat are not in force during "bein hashemashos" (the time between sunset and nightfall) e.g. we do not change out of our Shabbat clothes, we continue to wear leather shoes (which is forbidden on Tisha B'Av).

Not only that, but any week, if someone is not in the middle of a meal with bread, he needs to stop eating and drinking (except water) at sunset, because of the prohibition to eat before making Havdala.

  • I don't know where you get that second paragraph from. Many people only start their seudah shlishit after sunset and you can continue on by extending Shabbat. Only when you have said "baruch hamavdil bein kodesh l'chol" or recited the "ata chonantanu" have you "brought out" Shabbat thus you can't eat or drink before havdala (other than water).
    – CashCow
    Jul 25, 2016 at 9:20
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    @CashCow, from Halachipedia: Although it is forbidden to begin eating after sunset until one says Havdalah, [18] and it is definitely preferable to eat before sunset, [19] some poskim give extra time to begin the meal if one hasn't yet eaten seuda shlishit. [20] If one began eating before sunset he may continue after. [21] However, this doesn't apply if one was only drinking not as part of a meal [22] or to eating only mezonot or fruit, so one must stop if that is all that he is having. [23] halachipedia.com/index.php?title=Seudat_Shelishit
    – Miriam
    Jul 25, 2016 at 9:29
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    @CashCow, it is bedieved to begin seuda shlishit after shkiya, and then only in a limited time frame. You can only continue a full (bread) meal, but if you didn't start a meal with bread you can only drink water from shkiya (or the few minutes after shkiya if you rely on those poskim) on, not from when you make out Shabbat.
    – Miriam
    Jul 25, 2016 at 9:34

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