Version #1 - Rashi - (Mishnah): If one swore not to fulfill a Mitzvah and fulfilled it, he is exempt;

If he swore to fulfill a Mitzvah and did not fulfill it, he is exempt.

One might have thought to obligate him from a Kal va'Chomer, like R. Yehudah ben Beseira does;

Version #2 - Tosfos - (Mishnah - R. Yehudah ben Beseira): If one swore not to fulfill a Mitzvah and fulfilled it, he is exempt;

If he swore to fulfill a negative Mitzvah and did not fulfill it, he is exempt.

One might have thought to obligate him from a Kal va'Chomer; (end of Version #2)

One is liable (to bring the Korban for transgressing an oath of Bituy) for Reshus, and all the more so for an oath about a Mitzvah, for which he is already bound by the oath of Sinai!

Chachamim: This is not so (even for positive Mitzvos). One is liable for Reshus, for they apply in the negative just like in the positive;

He is exempt for an oath about a Mitzvah, since there is no liability for breaking an oath not to fulfill the Mitzvah.

(Gemara - Beraisa): Suggestion: If one swore not to fulfill a Mitzvah and fulfilled it, he should be liable!

Rejection: "Lehara Oh Leheitiv" - just like Leheitiv (to do good) does not refer to a Mitzvah (later, we shall explain how we know this), also Lehara (to do evil) does not refer to a Mitzvah;

This excludes one who swore not to fulfill a Mitzvah and fulfilled it. He is exempt.

Suggestion: If one swore to fulfill a Mitzvah and did not fulfill it, he should be liable.

Rejection: "Lehara Oh Leheitiv" - just like Lehara does not refer to a Mitzvah, also Leheitiv;

This excludes one who swore to fulfill a Mitzvah and did not fulfill it. He is exempt.

Suggestion: If one swore to harm himself and did not fulfill it, he should be exempt.

Rejection: "Lehara Oh Leheitiv" - just like Leheitiv is Reshus, also Lehara;

This includes one who swore to harm himself (Tosfos - our Tana allows harming oneself; Ran - since the Torah does not explicitly forbid this, an oath to do so takes effect) and did not fulfill it, he is liable.

Suggestion: If one swore to harm others and did not fulfill it, he should be liable.

Rejection: "Lehara Oh Leheitiv" - just like Leheitiv is Reshus, also Lehara;

This excludes one who swore to harm others (the oath did not take effect, since the Torah explicitly forbids this) and did not fulfill it. He is exempt.

Question: What is the source to include one who swears to benefit others?

Answer: We learn from "Oh Leheitiv."

An example of harming others is striking them.

Question: The Tana assumed that the verse discusses good and evil of Reshus. What is his source? Perhaps it discusses (even) Mitzvos! (Tosfos - evil could be an oath not to eat Matzah.)

Answer #1: It cannot be Mitzvos, for we equate Leheitiv and Lehara in both directions;

Just like Leheitiv (e.g. eating) cannot entail not fulfilling a Mitzvah (for that is detrimental to a person), also Lehara (e.g. not eating) cannot entail not fulfilling a Mitzvah;

Rather, Lehara must be fulfillment of a Mitzvah, (e.g. not eating Neveilos). However, this is included in Leheitiv!

Likewise, just like the case of Lehara (e.g. not eating) cannot entail fulfilling a Mitzvah (for that benefits a person), also Leheitiv cannot entail fulfilling a Mitzvah;

Rather, Leheitiv must be transgression of a Mitzvah (e.g. to eat Neveilos). However, this is included in Lehara!

Conclusion: The verse must discuss good and evil of Reshus.

Rejection: The same reasoning shows that it does not discuss good and evil of Reshus!

(Just like Leheitiv (e.g. eating) cannot entail eating harmful food (for that is detrimental), also Lehara cannot harm the body;

Rather, Lehara must be refraining from harmful food. This is included in Leheitiv!

Similarly, we may show that Leheitiv must be eating harmful food, but this is included in Lehara!

Answer #2: Rather, since the Torah had to write "Oh Leheitiv" to include benefiting others, we conclude that the verse discusses good and evil of Reshus;

If it referred to Mitzvos, having taught that oaths apply to harming others, there would be no need to teach that they apply to helping others!

Question: This answer is like R. Yonason. (We expound 'Oh', for the Torah could have written a 'Vov' (u'Leheitiv), and we would not have erred to think that the oath must discuss harm and benefit.) How can R. Yoshiyah answer?

(Beraisa - R. Yoshiyah): "A man who will curse Es Aviv v'Es Imo" teaches only if he curses both;

"Aviv v'Imo Kilel" includes even if he curses only one of them ('curse' is put adjacent to each parent).

R. Yonason says, a 'Vov' (and) connotes even one of them, unless the Torah explicitly says 'together' (like it does regarding Kilayim).

Answer: The Mishnah can even be R. Yoshiyah. He holds like R. Akiva (26a), who expounded the Ribuy, Mi'ut, Ribuy to include everything except for oaths about Mitzvos.

This can be only if the Torah discusses oaths of Reshus. If it discusses oaths about Mitzvos, there is nothing to exclude!

(Mishnah - R. Yehudah ben Beseira): If one is liable for an oath of Reshus...

Question: How does R. Yehudah answer Chachamim's rebuttal?

Answer: Even though an oath to harm others does not take effect, one is liable for an oath to benefit others, because the verse included it;

Similarly, even though an oath not to fulfill a Mitzvah does not take effect, one is liable for an oath to fulfill a Mitzvah, because the verse included it!

Chachamim disagree. An oath to benefit others applies also to the negative (not to benefit others), but an oath to fulfill a Mitzvah does not apply to the negative (not to fulfill the Mitzvah) at all!

(Mishnah): If one said 'I swear that I will not eat this loaf, I swear that I will not eat it, (I swear that I will not eat it - Tosfos deletes this)', if he eats it, he is liable only once;

This is the oath of Bituy for which one is lashed if he transgressed b'Mezid, and brings an Oleh v'Yored if he was Shogeg.

For Shevu'as Shav one is lashed if he transgressed b'Mezid, if he was Shogeg he is exempt.

(Gemara) Question: Why does the Tana change the expression from the first oath ('I will not eat this loaf') to the second ('I will not eat it')?

Answer: This teaches that only in this order, he is liable only once, but had he reversed the order, he is liable twice.

(Rava): If one said 'I swear that I will not eat this loaf', he is liable for eating a k'Zayis of it. If he said 'I swear that I will not eat it', he is not liable until he eats all of it.

(Mishnah): '... I swear that I will not eat it', if he eats it, he is liable only once.

Version #1 (Rashi) Question: Why does the Tana mention a third oath (obviously, if the second oath does not take effect, neither does the third!)?

Version #2 (Tosfos) Question: Why does the Tana say 'he is liable only once'? (end of Version #2)

Answer: He teaches that he is not liable, but the extra oath (or two) is there, if an opportunity comes, it (they) will take effect.

Question: When does it make a difference?

Answer: Rava taught that if he asks to annul the first oath (and a Chacham permits it), the second takes effect.

Suggestion: A Beraisa supports this.

(Beraisa): If a man accepted Nezirus two times, and conducted 30 days of (the first) Nezirus, separated Korbanos, and asked to annul the first Nezirus, he fulfills the second Nezirus through the days he conducted (and can use the Korbanos for it. This shows, if the second Nezirus has an opportunity to take effect, it does!)

Rejection: There is different, for the second Nezirus will surely take effect (if he does not annul the first Nezirus, it takes effect after the first Nezirus);

Here, the second oath was void when he uttered it!