Gemara

If one wants any vows he takes the entire year to be void, he should say on Rosh Hashanah 'Any vow that I will take should be void.' He must remember at the time of the vow.

Question: If he remembers at the time of the vow, he uproots his stipulation, and takes a valid vow!

Answer #1 (Abaye): We must amend the Mishnah to say 'provided he does not remember at the time of the vow.'

Answer #2 (Rava): The text of the Mishnah is correct. The case is, he stipulated on Rosh Hashanah, and forgot what he stipulated;

If at the time of his vow he remembers (that he stipulated, but forgot what he stipulated), and vows according to his stipulation, the vow is void;

If he does not say that he vows according to his stipulation, he uproots his stipulation and the vow is valid.

Rav Huna bar Chinena intended to expound this when teaching in public.

Rava: The Tana concealed this, lest people take vows lightly, and you want to teach this in public?!

Rishonim

The Rif and Rosh (3:5) bring our Gemara.

Rosh: The Gemara discussed a particular time (Rosh Hashanah). One may do so at any time. Rava agrees with Abaye, that if one forgot at the time of the vow, the vow is void. He merely shows that we need not alter the text of the Mishnah.

R. Tam (cited in Rosh): This is the source for Kol Nidrei on Yom Kipur. One stipulates that if he will vow out of anger in the coming year and forget the stipulation, the vow will be void. The custom is to say this on Yom Kipur, when everyone gathers in the Beis ha'Keneses. We find that Yom Kipur is called 'Rosh Hashanah' in Yechezkeil (40:1). R. Tam changed the text in Machzorim to say 'from this Yom Kipur until next Yom Kipur.' The old text said 'from last Yom Kipur until this Yom Kipur.' It was to permit vows to evade the punishment, in case one transgressed them. It does not help, for Heter Nedarim requires three commoners or an expert judge. (The Shali'ach Tzibur says Kol Nidrei alone. No one requires that he must be an expert judge, and nowadays, we have no expert judges.) Also, who permits the Nedarim of the Shali'ach Tzibur)? Also, Hatarah requires regret. Also, the Halachah follows Rav Papa who says that one must detail the Neder. R. Tam also fixed to say 'd'Nidrana ud'Ishtabana' (future tense, that I will vow and swear). We say it three times, like all Divrei Chachamim. E.g., one who will reap the Omer first asks three times 'is this a sickle?...' (Menachos 65a). We say "v'Nislach l'Chol Adas Bnei Yisrael", not to atone for past vows, rather, to atone for future vows, if someone will forget the Bitul, and vow and transgress it. Even though the vow is Batel, he needs atonement, for he intended to sin (Kidushin 81a). This helps for what one vows himself, but not for what someone else or Beis Din makes him swear.

Rebuttal (Rosh): The old custom is correct. The text of Kol Nidrei refers to past vows. This is why we say it three times, and we say "v'Nislach" to atone for those who transgressed. We are sure that anyone who transgressed a vow regrets that he ever vowed, to evade punishment. The entire congregation says it quietly, so we have three commoners. They permit the Shali'ach Tzibur's vows. The need to detail Nedarim is only when one goes to a Chacham, lest he seeks to permit a Neder to do a Mitzvah.

Beis Yosef (OC 619 DH Kosav ha'Kol): The Kol Bo (68:33b) says that if the Shali'ach Tzibur has a Safek Shevuah or Neder, he should permit it in front of three people before Kol Nidrei, for one cannot permit his own Neder. Nowadays, we do not do so. We rely on the Tzibur, which says Kol Nidrei with him, to permit him.

Taz (OC 619:2 DH Kosav ha'Tur): We cannot retroactively permit a vow due to fear of punishment for having transgressed it. If so, one would never be liable for slaughtering Kodshim outside the Mikdash, for surely he regrets that he made it Hekdesh, lest he get Kares!

Note: One who wants to anger Hash-m would not regret this. Or, he slaughtered a Bechor, which is Kodesh automatically, or another's Korban. Alternatively, he slaughtered the child or Temurah of a Korban that was offered properly. We do not permit Hekdesh after Hakravah (Tosfos Kerisus 13b DH Arba). These latter cases explain how one can be Chayav Chatas for Shogeg. However, it is difficult to establish every Chiyuv for Shechutei Chutz in Shas to be one of these special cases.

Taz (ibid.): The Tur says 'this was difficult to R. Tam', not 'R. Tam asked', because R. Tam did not explicitly say that a proper Pesach is required. The Rosh answered that had he known the punishment that comes from vowing, he would not have vowed.

Hagahos Maimoniyos (Minhagei Yom Kipur (after Hilchos Shevisas Asur) DH Kol): Ra'avan and early Gedolei Ashkenaz say that we permit last year's vows. It is said three times, like all Hataras Nedarim. R. Tam's text, to permit Nedarim of the coming year, does not apply to Cherem of the Rabim or Shevuos of Beis Din. Surely one of them remembers the stipulation.

Rosh (Yoma 8:28): Rav Sadya Gaon explicitly says that Kol Nidrei permits last year's vows. We say it before Borechu, because we permit vows on Shabbos (or Yom Tov) only for the needs of Shabbos. R. Natrunai Gaon says that it is not our custom to permit vows on Rosh Hashanah or Yom Kipur, but in other lands they say Kol Nidrei. We concluded like Rava, that we should not publicly teach how one may declare future vows to be void. All the more so we should not publicize permission of vows that took effect! Also, it does not help to say that now the vows should be void. Also Rav Hai says that we do not permit vows on Rosh Hashanah or Yom Kipur. One should not change from the custom.

Korban Nesan'el (10): R. Natrunai Gaon says that it does not help to permit the vows due to R. Tam's reasons.

Rivash (394 b'Sof, b'Inyan Kol Nidrei): The Ramban (Mishpat ha'Cherem) says that Kol Nidrei permits only mistaken vows, like the four vows, which require another Pesach. Surely it does not permit other vows and oaths! Rav Sadya Gaon explicitly says so. The Rosh bent over backwards to defend the old text. He does not say that it permits the vows. Rather, it is to evade punishment for having transgressed them. Perhaps this is why we may do so on Yom Tov, for it is not Hataras Nedarim. Alternatively, we say it before Borechu. The text shows that it is not Hataras Nedarim. We say that they should be 'Batel'. A husband may say 'Batel' to annul, but not a Chacham! Even though there are other expressions in Kol Nidrei that a Chacham may use, we should not begin the Heter with an invalid expression!

Note: If it is not Hataras Nedarim, it is not clear to me how this evades punishment for having transgressed them. If it is mere Teshuvah, why do we regret only the vows, and not transgressing them?

Conclusion (Rosh): Rava forbids publicly expounding the stipulation, lest Amei ha'Aretz be lenient about Nedarim. Since we permit vows that took effect, there is no concern.

Korban Nesan'el (30): Tosfos says that according to R. Tam, we say Kol Nidrei in Arame'ic, and Amei ha'Aretz do not understand it. SMaG says that it is not a problem because we do not say 'you are permitted.'

Kaf ha'Chayim (OC 619:14): It was enacted in Bavel, therefore an Arame'ic text was enacted so everyone would understand it (Levush and others).

Poskim

Shulchan Aruch (OC 619:1): On the night of Yom Kipur the custom is that the Shali'ach Tzibur says... Kol Nidrei.

Beis Yosef (DH v'Gam): The Mordechai (726) says that everyone intends for what the Shali'ach Tzibur says, so it is as if they said 'we regret.' We need not exclude enactments of the Tzibur or a decree of Cherem, since they do not consent to permit it.

Mishnah Berurah (1): Our custom is like R. Tam. The Tzibur must say it with the Shali'ach Tzibur, for his stipulation does not help for the Tzibur.

Note: R. Tam asked that Hataras Nedarim requires three, and no one permits the Shali'ach Tzibur. Perhaps he agrees that the Tzibur says it quietly with the Shali'ach Tzibur, but holds that they cannot join to permit, for no one can hear them. Alternatively, R. Tam holds that the Tzibur is silent, and the Mishnah Berurah has a different source to say that Reuven's stipulation cannot help for Shimon (unlike R. Tam).

Kaf ha'Chayim (18): The Levush and others say that the Shali'ach Tzibur's stipulation does not help for the Tzibur. Eliyahu Rabah disagrees. Maharil says that all agree that the Tzibur should say it with the Shali'ach Tzibur.

Kaf ha'Chayim (17): Radvaz (1:33) and Keneses ha'Gedolah say 'from last Yom Kipur until this Yom Kipur, and from this Yom Kipur until next Yom Kipur.'

Rema: The custom is to say Kol Nidrei three times, while it is still day.