(Mishnah): 'Konam wine that I will taste today', he is forbidden only until dark.

Explanation: Since he said 'today', this implies only until that day finishes, i.e. until it gets dark.

Mishnah: This Shabbos.

Explanation #1: If he vowed on one of the days of the week, he is forbidden all days of the week, and Shabbos itself is included in the Isur of the week that passed;

Source: When a person says 'this Shabbos', he intends for the coming weekdays, and for Shabbos. (In DH Shavu'a Zeh, the Ran brings another Perush of this and the coming expressions.)

Mishnah: This month.

Explanation #1: If he vowed on one of the days of the month, he is forbidden the entire month, and Rosh Chodesh is [part of] the coming [month];

Source: Rosh Chodesh after the days of the month is not included in the Isur. Rather, it is counted towards the coming [month], and it is permitted.

Mishnah: 'This year', it is forbidden the entire year.

Explanation #1: I.e. until Rosh Chodesh Tishrei. However, Rosh Chodesh Tishrei is considered part of the coming year, and it is not included in the Isur.

Explanation #1: [If one said] 'the years of this Shemitah", he is forbidden until the six years of Shemitah finish, and he is forbidden also in the seventh year. Its law is leshe'Avar (like the previous years). This is the Perush of our Mishnah.

Explanation #2: Others explained that [if one said'] "this Shabbos" he is forbidden the entire Shabbos, e.g. it is now Shabbos and he vowed and said "this Shabbos";

It teaches that he is forbidden the entire Shabbos (week), and [also] this current day of Shabbos, even though it is included in the week that passed. This is why it taught "and Shabbos is leshe'Avar."

If he said "this month", he is forbidden the entire coming month, and Rosh Chodesh is leha'Ba (like the coming month). E.g. if today is Rosh Chodesh. It teaches that he is forbidden the entire coming month, and [also] this day of Rosh Chodesh itself on which he vowed.

The Gemara asks that this is obvious!

Note: Nidrei Zerizin did not understand why the Ran says so here. The Gemara asked so also above, regarding one Shabbos! He suggests that these words belong at the end of this Dibur, in which the Ran refutes Explanation #2.

If he said "this year", e.g. he vowed on Rosh Hashanah, he is forbidden the coming year, and this day of Rosh Hashanah itself on which he vowed, for its law is leha'Ba;

If he said "this Shavu'a", he is forbidden the entire Shavu'a (Shemitah cycle), and Shevi'is is leshe'Avar. I.e. he vowed in Shevi'is, and said "this Shavu'a", and it teaches that he is forbidden all the coming years of Shemitah;

[He is forbidden also] this current year of Shevi'is, even though it is counted amidst the Shavu'a that passed.

Implied question: According to this Perush, why did it teach leshe'Avar regarding Shabbos and Shevi'is, and leha'Ba regarding a month and year? It could have taught all of these to be leha'Ba!

Answer: This was to teach about one who vows in the middle of these times. In the middle of the week or Shevi'is, he is forbidden the coming Shabbos and Shevi'is;

The law is different regarding one who vows in the middle of the month or year. He is permitted on the coming Rosh Chodesh or Rosh Hashanah.

Rejection: However, this Perush (Explanation #2) is wrong. Since he said this Shabbos or this Shavu'a, why is he forbidden the coming Shabbos or Shavu'a (Shemitah)?

We should have said that he is forbidden only on the current Shabbos day, or the current Shemitah year!

Support: We say in Rosh Hashanah (12b) that one who is Mudar Hana'ah from his friend for a year, if he said "this year", even if it was the 29th of Elul, once Tishrei 1 comes, this counts like the year (he is permitted).

Conclusion: The first Perush is primary.

Mishnah: And if he said 'one day...' he is forbidden for that amount of time, from day to day.

Explanation: I.e. one duration. Regarding 'one day' he is forbidden me'Es la'Es (24 hours).

Gemara: When it gets dark, he must ask a Chacham.

Explanation: Even though based on letter of the law, when he said 'today', he is permitted when it gets dark, like it says in our Mishnah, even so, mid'Rabanan he must ask.

Gemara: Rav Yosef said, this is a decree [when he said 'today'] due to when he says 'one day.'

Explanation: If you will permit him when it is dark without asking [a Chacham], he will come to err about 'one day', to think that also then he is permitted after dark;

He does not think that there is any difference between 'one day' and 'today'.

Gemara: 'Today' is confused with 'one day.'

Explanation: If you will permit him after dark when he said 'today' without asking, he will come to permit also even when he said 'one day';

Distinction: 'One day' is not confused with 'today', for when he said 'one day', he stood in his Isur me'Es la'Es. Therefore, he will not be confused to permit 'today' before dark.

Implied question: The custom nowadays is that an individual's fast is only from morning to evening, and even so, at dark he is permitted without She'elah. Why don't we decree due to [one who vowed to fast] one day?

Answer: This is because it is known that this is the law of a fast. Its Isur is not like other Nedarim for which Chachamim already fixed a time;

Therefore, even if you permit him at dark, he will not come to confuse this with one who vows for one day, for the laws of Ta'anis and Nedarim are different. People will not mix them up. So it seems to me.

Remark: I disagree with what the Rashba wrote here.

Answer #2 (Rashba): The reason we decree about one who said "today" is because part of the day was permitted to him at the beginning, it is as if he said "one day." Since these resemble each other, he will come to confuse them.

Distinction: However, a fast is forbidden from the beginning of the day. This is unlike one day. He will say "the reason here I am permitted when it gets dark, is because I was forbidden at the beginning of the day;

However, [when he said] "one day", its Isur does not take effect from its (the day's) beginning. It is not proper that he be permitted at the end of the day.

Rebuttal: I disagree. When one says "today", we obligated him She'elah when it gets dark...

Isn't this [even] if it was before dawn when he vowed, and he was forbidden from its beginning, like an individual's fast? Rather, surely it is like we said.

Consequence: Due to this reason, one who accepts on himself to fast 'one day in the week', we do not obligate him to fast for 24 hours;

Surely he intended for the fast that Chachamim said, i.e. from before dawn until dark.

Explanation: This that we obligate She'elas Chacham when he said "today" is not only due to a decree;

We hold that this is not so common to confuse them, that just for a decree we would be stringent about this. However, since he vowed, he did improperly, like R. Nasan's teaching...

Implied suggestion: Even if it were not applicable at all to decree, we would be stringent and obligate him She'elah!

Rejection: If so, also regarding all vows, when their [ending] time comes, we should say so!

However, whenever it is applicable to decree, we are stringent upon him and fine him.

Consequence: Therefore, if he vowed about a Mitzvah, e.g. to learn or fulfill a Mitzvah, he does not need She'elah.

Reference: R. Nasan's comparison of one who vows to one who builds a Bamah, I explained this above (22a) with Hash-m's help.

Explanation: The law of Shabbos is like leshe'Avar (the previous week). One might have thought that he refers to days of the week;

Because weekdays are called 'days of Shabbos' (i.e. Rishon b'Shabbos, Sheni b'Shabbos...), we should say that he intended only for them, and not to forbid to himself wine on Shabbos! The Mishnah teaches that this is not so.

Alternate text: Some texts say "one might have thought that he refers to days before Shabbos. The Mishnah teaches that this is not so." This means the same [as our text].

Limitation: However, we cannot explain this text at all according to the latter Perush that we explained in our Mishnah, that we discuss one who vows on Shabbos.

Gemara: It is needed for a Chaser month (of 29 days).

Explanation: The month after the month of his vow is Chaser. If so, the month that he vowed in was full, and they make in the coming Chaser month two days of Rosh Chodesh. The first day is to fill the month that passed.

Note: Indeed, normally months alternate - full and Chaser. However, if the Gemara means that he vowed in a full month, why did it not simply say 'Chodesh Malei'? (PF)

Gemara: What might I have thought - Rosh Chodesh is from the past month.

Explanation: This is because the first day of Rosh Chodesh is to fill the past month. One might have thought that he is forbidden on it.

Gemara: [The Mishnah] teaches that this is not so, for people call it Rosh Chodesh.

Explanation: Therefore, even though it is included in the first month, since people call it Rosh Chodesh, he is permitted in it, for in Nedarim we follow Leshon Bnei Adam (how people speak).

Inference: Also in documents, on the first day of Rosh Chodesh, one writes "b'Yom Chodesh Ploni." He does not write the name of the previous month;

If he did, the document is predated and Pasul, for the document was made in the second (new) month, and people will say that it was made earlier [in the old month];

This is because in Leshon Bnei Adam, the first day of Rosh Chodesh of the new month is not called with the name of the old month.

On the second day of Rosh Chodesh, he writes "b'Yom Sheni of Chodesh Ploni." The next day, he writes "the third day." If he will write "the second day", it is Pasul, for it is predated;

Since regarding Nedarim, we say that the first day of a Chaser month is called Rosh Chodesh, we judge documents similarly.

Source: Below (63a), we compare documents to Nedarim.

Support: This is proper, for in all places, documents and obligations are based on Leshon Bnei Adam (like Nedarim are).

Distinction: However, the Rashba wrote in the name of Tosfos that in Gitin, one must write [e.g.] "on the 30th day of Tishrei, which is Rosh Chodesh Cheshvan", in order to be stringent.

Gemara: They asked - is its law like 'ha'Yom'?

Explanation: If so, he is permitted after dark. Or, is it like 'one day', and he is forbidden me'Es la'Es?

Gemara: He is forbidden in it and in its Ibur (the added month).

Assertion: It seems to me that the Chidush that he is forbidden in its Ibur is needed for one who vowed from the beginning of the year;

One might have thought that he is forbidden only in 12 months, like most years. [The Mishnah] teaches that this is not so; he is forbidden for 13;

If he vowed on Rosh Chodesh Shevat, this is obvious, that 'the year' implies until Rosh Hashanah!