Many times in Halacha we find that one should repeat if forgetting something. For example, on Rosh Chodesh (by Shacharis or Mincha), one must repeat Shemonah Esrei if s/he forgot Yaaleh Veyovo. On shabbos one must repeat Bentching if forgot Retzei. Etc...

Why is this necessary? What does it accomplish? And, doesn't it come under possible Brocho l'vatalahs?

  • What do you mean "what does it accomplish"? It gives you the chance to say the forgotten prayer!
    – mevaqesh
    Commented Nov 12, 2017 at 1:36
  • @mevaqesh Well then you can simply say the forgotten prayer. The question is asking why the need for the repetition of the prayer you already said.
    – yydl
    Commented Nov 12, 2017 at 22:33
  • You don't seem to be assuming that there is any necessity for the structure of prayer and that you are free to add a prayer out of place. Why would you assume this?
    – mevaqesh
    Commented Nov 12, 2017 at 22:52
  • @mevaqesh Well why not assume this? As an example, Shemonah Esrei consists of 19 brachos. Yaaleh Veyovo is a component of just one of those brachos. Maybe just repeat that bracha?
    – yydl
    Commented Nov 12, 2017 at 22:56
  • You can't just make up assumptions, and ask based on them. Well, you can, but it makes for a horrible question. || The very existence of shmoneh esrei as a formal prayer divided into three components in a particular order, each divided into sub-blessings suggests that structure matters in prayer, and its not just a free for all. || Regardless, this shows no research effort...
    – mevaqesh
    Commented Nov 12, 2017 at 22:58

1 Answer 1


The basic idea, as I understand it, is that if these parts were omitted, it's a case of meshaneh mimatbeya shetav'u chachamim - altering the fundamental text that the Sages instituted for the prayers. This itself invalidates the prayer.

So for example, the correct text of Shemoneh Esreh on Rosh Chodesh is supposed to include Yaaleh Veyavo. If one leaves that out, then, effectively the person has not said Shemoneh Esreh properly - it would be as though they omitted one or more of the regular blessings.

There are some cases where it's questionable where one should repeat the prayer because of such an omission (because there is the counterbalancing concern of a berachah levatalah, a blessing in vain, as you noted). In some such cases, the posekim recommend repeating Shemoneh Esreh as a voluntary (nedavah) prayer, which one is anyway permitted to do (see, for example, Taz to Orach Chaim 118:2 and 582:1).

  • Is it not the case that we do not do Tefillos Nedavah Today? Commented Jun 14, 2010 at 4:00
  • 1
    That's what Chayei Adam (27:17) says. However, Mishnah Berurah (Beur Halachah 107:1) strongly disagrees. He says that while it is true (per Shulchan Aruch ibid. :4) that in order to pray Tefillas Nedavah one must be certain that he is able to concentrate properly throughout all of it, this does not apply to a TN done because of uncertainty as to whether one recited the appropriate additions to Shemoneh Esreh, and one may (or should) do so even if it may be difficult to have kavvanah throughout all of it.
    – Alex
    Commented Jun 14, 2010 at 4:40
  • Sorry but I am Guessing TN is Tefillas Nedavah? Commented Jun 14, 2010 at 5:07
  • Yes, that's correct.
    – Alex
    Commented Jun 14, 2010 at 19:20

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