1.Error, Omission, and Interruption in the Amidah
A person who skips one of the eighteen berachot in the Amidah does not fulfill his obligation of the mitzvah of prayer. Even if he does actually recite the full Amidah, but rearranges the order of the berachot, he does not fulfill his obligation. This is because Anshei Knesset HaGedolah, who instituted the wording of prayer, meticulously established the order of the berachot of the Amidah and based their carefully selected words on verses of Scripture (Megillah 17b; Shulchan Aruch 119:3).
Additionally, a person who makes a mistake in one of the berachot, such that it alters the essence of the berachah, is considered not to have recited that berachah at all. This holds true for one who omits the end of a berachah, or inserts words that do not belong at all, like requesting rain in the summer (Bei’ur Halachah 119:3).
One who completes the Amidah and then remembers that he omitted words or erred in one of the berachot must repeat the entire Amidah. Even if he has not yet taken three steps back, if he finished the prayers of supplication and is about to take steps backwards, he must return to the beginning of the Amidah (Shulchan Aruch 117:5).
If he has not yet concluded the Amidah and remembers that he omitted words or made a mistake in one of the thirteen middle berachot, he must return to that berachah and continue praying from that point on, in the correct order. Even though he repeats the berachot that he already recited, since everything after that berachah was not recited in order, it is as if he did not say them at all, and he must recite them again in their correct sequence.
If one skips words or errs in one of the first three berachot, or in one of the last three berachot, he must go back to the beginning of them. Since the first three berachot possess one theme, as do the last three berachot, (see earlier in this book 17:10), each section is considered one unit. Therefore, anyone who makes a mistake in one berachah is considered to have erred in all of them and must repeat all three of them from the beginning (Berachot 34a; Rama 114:6).
The law concerning a person who interrupts Shemoneh Esrei in the middle, whether with speech or silently, is as follows: if the interruption is short, he continues praying from the point at which he stopped. However, if the interruption is long, enough that he could have finished praying the entire Amidah from beginning to end, he returns to the start of the Amidah. Some say that there is no difference between an intentional interruption and one due to circumstances beyond his control. In either case, since there was enough time for him to finish the entire Amidah, he starts from the beginning (Shulchan Aruch 104:5). Others say that he only returns to the beginning of the Amidah if the interruption was due to circumstances beyond his control; however, if he interrupted willingly, even after a long interruption, he returns to pray from the place at which he stopped (Rama 65:1; Mishnah Berurah 104:16). 1
2.Additions Pertaining to Particular Days
On special days, prayers that pertain to that specific day are added. There are additions that, if forgotten, prevent one’s fulfillment of his obligation, and there are additions that l'chatchilah must be recited, but b’dieved, if not included, do not prevent a person from fulfilling his obligation.
On Chol HaMo’ed Pesach and Sukkot, the Ya’aleh V’Yavo prayer is added in Birkat Retzeh. If a person forgets to say it, he must repeat the Amidah. If he did not finish the Amidah yet, he goes back to Retzeh, recites Ya’aleh V’Yavo, and from there continues on until the end of the Amidah. Similarly, we recite Ya’aleh V’Yavo on Rosh Chodesh. If it was omitted in Shacharit or Minchah, the Amidah must be repeated. However, if forgotten in Ma’ariv of Rosh Chodesh, it is not recited again, because when the new month was sanctified in Jerusalem based on the testimony of witnesses, there was no sanctification at night. Therefore, the sanctity of Rosh Chodesh does not yet apply in Ma’ariv (Shulchan Aruch 422:1).
On Motza’ei Shabbat we add the Havdalah wording in Birkat Attah Chonen of the Amidah. If forgotten, it is not repeated since the person praying will fulfill his obligation afterwards, in the Havdalah ceremony performed over wine (Shulchan Aruch 294:1).
On Chanukah and Purim, Al HaNisim is added in Birkat HaHoda’ah. If a person forgets to recite it, he does not go back, since these holidays are rabbinic. Therefore, forgetting to mention them in the Amidah does not prevent one from fulfilling his obligation (Shulchan Aruch 682:1).
On fast days, individuals add Aneinu in the berachah of Shome’a Tefillah. Ashkenazim only recite it in Minchah (Rama 565:3). Sephardim recite it throughout the whole fast: on Tish’ah B’Av – in Ma’ariv, Shacharit, and Minchah; on the other fast days – in Shacharit and Minchah (Kaf HaChaim 565:17). Some are accustomed to reciting it in Ma’ariv on all fast days (Rav Rakach, Maharitz). According to all minhagim, one who forgets to say Aneinu does not repeat the Amidah.
During the Ten Days of Repentance, which are days of judgment, for during that time Hashem’s Kingdom is revealed in the world, we conclude the third berachah with the words, "HaMelech HaKadosh," and conclude Birkat Hashivah Shofteinu with the words, "HaMelech HaMishpat." If one mistakenly says "HaKel HaKadosh" in the third berachah and does not correct himself as he recites it (toch k’dei dibur), he must return to the beginning of the Amidah since, as we already learned, the first three berachot are considered one unit and anyone who makes a mistake in one of them must go back to the beginning. If a person accidentally concludes Birkat Hashivah Shofteinu as usual, "Melech ohev tzedakah u’mishpat" and does not correct himself while reciting it (toch k’dei dibur), according to the custom of Ashkenazim and some Sephardim, b’dieved he fulfills his obligation, because even in the wording recited throughout the whole year, the word "Melech" (King) is used (Rama 118:1; Ben Ish Chai, Nitzavim 19; Kaf HaChaim 1). Other Sephardim maintain that he does not fulfill his obligation because he did not recite the High Holy Days wording. Therefore, if he has not yet finished his Amidah, he must return to Birkat Hashivah Shofteinu, conclude it appropriately, and continue from there until the end of the Amidah. If he already finished reciting the Amidah, he must pray again, while stipulating that if he was not obligated to repeat the prayer, the second prayer is considered voluntary (nedavah) (Shulchan Aruch 118:1; Yechaveh Da’at 1:57).
There are four other additions made during the Ten Days of Repentance: "Zochreinu," "Mi Kamocha," "U’chetov," and "B’Sefer Chaim." If any of them are forgotten, the Amidah is not repeated (Shulchan Aruch 582:5).
If a person accidentally recites Ya’aleh V’Yavo, Zochreinu, or Al HaNisim on a regular weekday, he must go back to the beginning of the berachah. If he already went on to the next berachah, he continues despite his mistake. 2
3.The Voluntary Prayer (Tefillat Nedavah) and Laws in Situations of Uncertainty
The Chachamim instituted three daily prayers: Shacharit, corresponding to the morning Tamid offering; Minchah, corresponding to the Tamid of the afternoon; and Ma’ariv, corresponding to the raising of the organs and fats upon the altar. Just as when the Temple existed and every individual was permitted to bring voluntary offerings, so too, an individual is permitted to recite an additional voluntary Shemoneh Esrei. In order for his prayer to be recognized as voluntary, he must add some sort of special personal request in that prayer. We do not offer a Musaf offering voluntarily, therefore, one may not recite Musaf voluntarily. And just as we do not offer voluntary offerings on Shabbatot and festivals, so too, there are no voluntary prayers on those days (Shulchan Aruch 107:1-2). Anyone who wants to say a voluntary prayer must be certain that he is careful and capable of having kavanah in his prayer from beginning to end. If he cannot concentrate well, it is best that he does not recite a voluntary prayer at all (Shulchan Aruch 107:4). Nowadays, the accepted teaching is that we do not recite voluntary prayers because we do not have the proper kavanah.
One who is uncertain as to whether or not he recited one of the three daily prayers, as long as the time for its recital has not yet passed, he recites the prayer and makes a stipulation in his heart. He thinks, "If I already prayed, this prayer is considered a voluntary prayer, and if not, this is an obligatory prayer." It is unnecessary to introduce any personal requests into that Amidah, since the fact that he is avoiding uncertainty is itself the innovation. Even though we do not recite voluntary prayers nowadays, we are permitted to do so in order to avoid uncertainty. If, in the middle of that Amidah, one remembers that he already prayed, he continues to recite the Amidah until the end and adds a personal request to illustrate that it is, indeed, a voluntary prayer. This is allowed because he made a stipulation in the beginning of his prayer explaining that his Amidah should be considered voluntary if, in fact, he already prayed.
If a person starts to pray on the basis that his prayer is obligatory, thinking that he did not yet pray, but suddenly remembers in the middle of his Amidah that he already did, he must stop immediately. His prayer cannot become voluntary, for just like there is no offering that is partly obligatory and partly voluntary, so too, there is no prayer that begins as obligatory and ends as voluntary (Shulchan Aruch 107:1).
One who is daydreaming in the middle of his prayer to the point where he is unsure what part of the Amidah he is reciting, for instance, a person who is pondering whether he is reciting the sixth berachah or the tenth, according to most poskim, in order to avoid uncertainty he must return to the sixth berachah and start to pray from that point on. 3
^ 1.The poskim disagree as to what the law is concerning a person who purposely (b’meizid) talks in the middle of the Amidah. Some say (Shulchan Aruch, Taz, and Kaf HaChaim 104:33) that he is considered like anyone who interrupts in the middle of his prayer. Others say (Bach, Magen Avraham, and Chayei Adam) that since he interrupted intentionally, he rendered his prayer invalid and he must return to the beginning of the Amidah. See also Bei’ur Halachah 104:6.
^ 2.Some poskim say that since he recited words that do not belong there at all, he must go back to the beginning of the berachah in which he made the mistake. If he erred in the first three or last three berachot, he returns to the beginning of them. However, if he already finished the Amidah, he must start the Shemoneh Esrei again. This is on condition that he recited an outright falsity, such as in Ya’aleh V’Yavo, the words "b’Yom Rosh HaChodesh hazeh" or in "Zochreinu l’Chaim", the words "v’kotveinu," when it is not the time of inscription (ketivah). However, if he only recited the beginning of Ya’aleh V’Yavo or such similar additions, it is not considered an interruption and he continues praying. That is what the Knesset HaGedolah, Pri Chadash, and Mishnah Berurah 108:37-38 write. In contrast, the Shulchan Aruch 108:12 maintains that even if one said, "b’Yom Rosh HaChodesh hazeh" or other similar words, even though it is incorrect, it is not considered an interruption. A number of prominent Acharonim agree with him, among them, Magen Avraham 693:1 and Da’at Torah 668, as well as Kaf HaChaim 108:58. However, in practice, perhaps it is possible to say that even according to the Mishnah Berurah one does not repeat other berachot for such a mistake. Only if he did not finish the berachah in which he erred does he go back to the beginning of it, but if he already finished, he does not repeat it. The same holds true for the first or last three berachot; he does not return to the beginning of all of them, rather only to the beginning of the specific berachah in which he made the mistake. Therefore, in practice, it is not clear that he disagrees with the Shulchan Aruch concerning a mistaken addition which requires reciting another berachah, as I have written above.
^ 3.According to the Chayei Adam 24:21, he starts from the berachah that he knows for certain he has not yet recited. However, most poskim maintain that he must continue after the last berachah that he clearly remembers saying, so that there will be no doubt as to whether or not he skipped one of the berachot. This is what is written in Kaf HaChaim 119:20, Yabia Omer 2:9, and Yalkut Yosef, part 1, p. 206.
Regarding a person who is uncertain as to whether or not he prayed at all and must pray another Amidah as a voluntary prayer, the Bei’ur Halachah 107:1 s.v. "Im" writes that in the opinion of the Chayei Adam, nowadays he may not pray a voluntary prayer even with a stipulation. However, this opinion is not accepted.