1) "HAKAMAH B'LEV" -- UPHOLDING A NEDER IN ONE'S HEART
QUESTION: The Gemara cites a Beraisa that states that a husband or father may uphold a Neder in his heart ("Hakamah b'Lev" -- a Hakamah performed through thought alone), but he cannot be annul a Neder in his heart. The Beraisa does not give a source for its ruling that Hakamah in one's heart is valid.
The RAN explains that the source that Hakamah b'Lev is valid is the law that silence on the day he hears the Neder (Shetikah b'Yom Sham'o) is considered a Hakamah (see Insights to 69:1). The reason silence is considered Hakamah is that since the husband intentionally did not take advantage of the opportunity to do Hafarah, he acknowledges that he wants the Neder to be upheld. That acknowledgement suffices even though it was not articulated. Since silence on "Yom Sham'o" serves as Hakamah, Hakamah also should be valid when it is done in one's heart and is not articulated verbally.
REBBI AKIVA EIGER (in Gilyon ha'Shas) asks a strong question on the Ran's suggestion that the source for Hakamah b'Lev is the law that silence on the day he hears the Neder is considered Hakamah. When a person is silent, it is clear to all that he intends to uphold the Neder because, as the Ran writes, his silence reveals what is in his heart (that he wants the Neder to be upheld). This is what the Gemara commonly calls an "Umdena," evidence based on circumstance which makes his intention understood to all. The Gemara considers an Umdena to be much stronger than a thought in a person's mind which nobody else knows about. The general rule is "Devarim sheb'Lev Einam Devarim" -- thoughts in one's heart are not binding (until they are verbalized). If a person thinks a condition in his mind when he makes a Kinyan, the condition is not binding since he did not articulate it verbally. Nevertheless, if there is an Umdena that he had that condition in mind when he made the Kinyan, it is binding (Kesuvos 79a).
How, then, can the Ran prove that Hakamah in one's heart -- where there is no Umdena -- is effective from the Halachah of silence on the day of the Neder, where there is an Umdena?
ANSWER: The ACHIEZER (2:19) explains that there different Halachos have different reasons for why Dibur, speech, is required. When a person makes a Kinyan or gives a Get, why must one verbalize the conditions upon which the Kinyan or Get is contingent? One might have thought that it is because conditions that are not verbalized are "Devarim sheb'Lev" and are thus ineffective because "Devarim sheb'Lev Einam Devarim." However, the RASHBA (Kidushin 50a) explains that "Devarim sheb'Lev Einam Devarim" applies only when the words a person says contradict what he claims to have thought in his mind. For example, when a person expresses his consent to a Kinyan and specifies no condition, his words imply that his Kinyan is unconditional, and whatever he thinks in his mind is not strong enough to override those words. (It is not that the thoughts in his mind are meaningless, but rather that the thoughts in his mind do not express one's intention as clearly and as strongly as spoken words do. The logic behind this is as follows. Had he been conclusively decisive about the condition that he thought, he would have expressed it openly. The fact that he did not state it openly shows that he was unsure that he wanted it.) In such a situation, where his thoughts contradict his words, a thought which is understood to all through an Umdena is stronger than the words he utters. Since in such a case everyone is aware of his intentions, the thought (with the support of the Umdena) is able to override the words he expressed explicitly.
In contrast, when something takes effect entirely through thought (Machshavah) and no speech is involved (because the matter does not involve an interaction or agreement between people), what he thinks in his mind is effective and the principle of "Devarim sheb'Lev Einam Devarim" does not apply. For example, when a person designates certain fruits as Terumah in his mind but he says nothing, the principle of "Devarim sheb'Lev Einam Devarim" does not apply and does not prevent the Terumah from taking effect, since his thoughts are not contradicted by anything he said. The same applies to having a thought to make an object Hekdesh.
Accordingly, in the case of Hakamah (or, more generally, in the case of all Nedarim), "Devarim sheb'Lev Einam Devarim" is not a reason to require that he express his thoughts through speech, because he uttered no words which contradict his thoughts.
Why, though, would one have thought that Hakamah needs to be articulated verbally if the Torah had not taught otherwise? The answer is that one would have learned the Halachos of Hakamah from the Halachos of Nedarim, and the Gemara in Shevuos (26b) derives from a verse that Nedarim and Shevu'os must be articulated verbally.
However, if this is the reason why one would have thought that Hakamah must be spoken and not just thought, it emerges that thoughts that are understood through an Umdena are no stronger than thoughts that are not supported by an Umdena. The reason why he must articulate his thoughts is not in order to reveal his intentions, but rather in order to fit the proper format of a Neder; even if there is an Umdena, thoughts in one's mind do not fit the proper format of a Neder. Therefore, once the Torah teaches that thought does work to make a Hakamah (whether or not the thought is an Umdena), the format of a Neder is not necessary for Hakamah and there should be no reason to require an Umdena! A simple thought in the person's mind should suffice because there is no reason why thought should not be effective (since "Devarim sheb'Lev Einam Devarim" does not apply, as the Rashba explains, and because the requirement of "Bituy Sefasayim" does not apply, as derived from the fact that the format of a Neder is not necessary for Hakamah)!
The Acharonim, however, question the Achiezer's answer. The RAN in the beginning of Pesachim (DH Mahu) seems to disagree with the Rashba and understands that even when the thoughts in one's heart do not contradict what a person says, the thoughts are still not effective. The Ran writes that "Bitul Chafetz b'Lev," nullifying one's Chametz in his heart, cannot work through the mechanism of making the Chametz into Hefker; Hefker cannot be done in the person's mind because "Devarim sheb'Lev Einam Devarim." When a person makes something Hefker in his mind, he does not contradict any words that he said, and yet the thoughts in his mind are still not effective!
The answer to this question might be that the Ran there maintains that Hefker is an interaction between one person and all the other people in the world; by making his object Hefker, the owner puts his object into a state which allows all other people to take it. Consequently, if he does not tell other people that his object is Hefker, even though he did not say that his object is his it is understood from his actions and his lack of words that the object is still his. Therefore, his thoughts still contradict his actions and his silence.

79b----------------------------------------79b

2) "HAFARAH" OF "NEDARIM SHE'BEINO L'BEINAH"
QUESTION: The Mishnah (79a) states that the husband may annul the Nedarim of his wife when her Nedarim entail physical suffering (Inuy Nefesh). The Gemara understands from this statement of the Mishnah that this is the only type of Neder which the husband may annul, and he cannot annul Nedarim involving matters between him and his wife (Nedarim she'Beino l'Beinah). The Gemara asks that the Beraisa clearly states that the husband may annul this type of Neder as well.
The Gemara suggests that when the Mishnah says that the husband may annul Nedarim of Inuy Nefesh, it refers to the husband's right of absolute Hafarah: he may revoke those Nedarim totally. In contrast, when the Beraisa says that the husband may annul Nedarim she'Beino l'Beinah, it refers to partial Hafarah; such Nedarim are revoked only for as long as they are married. If he divorces her, the Neder returns.
The Gemara refutes this suggestion. The Mishnah later (85a) states that when a woman who makes a Neder that whatever she earns should be forbidden to her husband, the husband does not need to annul the Neder since she is obligated to give him her earnings. Rebbi Yochanan ben Nuri says that the husband should annul her Neder so that in case he later divorces her, the Neder will not take effect and prohibit them to remarry each other. Rebbi Yochanan Ben Nuri's opinion clearly implies that even when a husband annuls a Neder she'Beino l'Beinah, the Hafarah is valid even after divorce.
The Gemara instead answers that the Hafarah of Nedarim of Inuy Nefesh works both for himself and for others, while the Hafarah of Nedarim she'Beino l'Beinah works only for himself. However, even Hafarah of Nedarim she'Beino l'Beinah is effective for after he divorces her.
The Gemara implies that the Hafarah of Nedarim she'Beino l'Beinah is not effective only with regard to other people. With regard to the husband, the Hafarah is in effect even after he divorces her and has not yet remarried her. Why should the Hafarah be effective after he divorces her if, at that point, the Neder is no longer something that is Beino l'Beinah?
ANSWERS:
(a) The RAN, ROSH, and TOSFOS explain that when the Gemara says that the Hafarah is effective for himself, it means that it is effective for as long as she is fit to be married to him or to remarry him. When the Gemara says that the Hafarah is not in effect for other people, it means that if she marries another man and thereby becomes unfit to remarry her first husband, the Hafarah ceases to be in effect both for him and for others. The reason why the Hafarah remains in effect even after the divorce is that if the Hafarah would cease to work and the Neder would return, it would not be possible for the Hafarah to take effect again when he remarries her. In order for the Hafarah to take effect when he remarries her, it must not cease to be in effect after the divorce until it becomes clear that he will not remarry her (i.e. she marries someone else).
(b) The RAMBAM (Hilchos Nedarim 12:7) interprets "for himself" and "for others" differently. He writes that even while they are married, the Neder is revoked only inasmuch as it relates to the husband. For example, if a woman made a Neder not to eat locally-grown figs, she may eat locally-grown figs which her husband brings to her but that figs which others bring to her.
The KEREN ORAH explains that the Rambam, who does not explain "for himself" to mean after they are divorced and as long as she is fit to remarry him (i.e. she has not yet married someone else), actually maintains that the Neder takes effect even with regard to the husband as soon as he divorces her. If he remarries her, the Neder once again becomes invalid because of the original Hafarah. (See Rambam, Hilchos Nedarim 12:3, and Lechem Mishneh there.) According to the Rambam, Hafarah does not remove the Neder entirely but merely limits to whom the Neder applies. Hence, during the time that he divorced her and she did not remarry anyone else, the Hafarah was still present even if it did not apply to anyone in practice.
The Keren Orah continues to explain that the Rambam maintains that the Torah empowers the husband to annul the Neder only to the extent to which it interferes with their married life. Therefore, the Neder remains valid with regard to everyone else. Similarly, for that reason the Neder is also valid with regard to him for any time that they are not actually married.

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