Gemara

23a (Mishnah): R. Eliezer ben Yakov says, even one who wants to vow to pressure his friend to eat by him, should say 'any vow that I will take should be void.' He must remember at the time of the vow.

23b - Question: Do Chachamim disagree with R. Eliezer?

Answer #1 (Mishnah (63b)): If Reuven told Shimon 'I may not benefit from you if you will not take from me a Kor of wheat and two barrels of wine for your son', Shimon can permit the vow without a Chacham;

He can say 'you vowed only for my honor. This itself is my honor (that people see that you wanted to give to me, and I did not want to take).'

Inference: Had he not said this, the vow would be binding.

Suggestion: This is not like R. Eliezer. He calls this is a vow of urging (and it is permitted)! Rather, it is like Chachamim; they disagree with R. Eliezer.

Rejection: Really, it is like R. Eliezer. He agrees that this is a real vow. Reuven does not want to be like a dog, to take from Shimon without giving in return.

Answer #2 (Mishnah (63b) - R. Meir): If Reuven said to Shimon 'you may not benefit from me if you will not give to my son a Kor of wheat and two barrels of wine', the vow is binding until Shimon gives;

Chachamim say, Reuven can permit his own vow without a Chacham. He can say 'I consider it as if I received.'

Inference: Had he not said this, the vow would be binding.

Suggestion: This is not like R. Eliezer. He says that this is a vow of urging! Rather, it must be Chachamim, and they disagree with R. Eliezer.

Rejection: Really, it is like R. Eliezer. He agrees that this is a real vow. Reuven is not a king, he cannot constantly give to Shimon without receiving in return.

Rishonim

The Rif and Rosh (8:4) bring our Mishnah (63b).

Rosh: If he did not say 'it is as if I received', it is a Neder, not a Neder of urging. In the Reisha, it is because Reuven does not want to be like a dog, to take from Shimon without giving in return. In the Seifa, it is because Reuven is not a king. He cannot constantly give to Shimon without receiving in return.

Rambam (Hilchos Nedarim 8:14): If Reuven vowed or swore that Shimon must take from him a Kor of wheat or two barrels of wine, Shimon can permit the vow without a Chacham. He can say 'you intended to honor me. It is my honor not to take. I was already honored that you vowed for me!' Similarly, if Reuven vowed or swore that Shimon not benefit from him if he will not give to Reuven's son a Kor of wheat or two barrels of wine', Reuven can permit this without a Chacham. He says 'I consider it as if I received.' The same applies to all similar cases.

Ran (24a DH Klum): The Yerushalmi says that if each says 'the vow was for my honor', i.e. the Noder says 'I wanted to be honored by your acceptance', it does not help for the Mudar to say 'it is as if I received.' If both say that it was for the Mudar's honor, all agree that the Mudar can permit it by saying 'it is as if I received.' R. Meir and Chachamim argue about Stam.

Beis Yosef (YD 232 DH v'Chosav Sham): The Rosh (8:4) brought only the Seifa of this Yerushalmi. It seems that his text omitted the Reisha, for only the receiver is honored. Surely, the Noder intended for the Mudar's honor.

Rebuttal #1 (Korban Nesan'el 8:300): If so, what do the Tana'im argue about?

Rebuttal #2 (Shirei Korban 10b): Kidushin 7a says that one who gives to someone important is honored, and he can Mekadesh a woman with the Hana'ah! Also, why did the Gemara need to say that they argue about Stam? They could argue about when each says 'it was for my honor'!

Poskim

Shulchan Aruch (YD 232:20): Another Neder that need not be permitted is if Reuven told Shimon 'I may not benefit from you if you will not take such and such from me.' Shimon can permit the vow without a Chacham, by saying 'you vowed only for my honor. This itself is my honor, that I will not take.' This is even Stam, when Reuven does not say that this was his intent.

Rivash (387, brought in Beis Yosef 336 DH Kosav ha'Rivash): Reuven made the vow contingent on Shimon, therefore it is permitted only if Shimon says 'this is my honor...' If Reuven vowed 'if I do not give to you', he meant that he will offer to give. Even if Shimon declines to accept, it is permitted.

Levush: Why isn't this like vows or urging, which are permitted without saying 'it is as if I ate by you'? It seems that one who declines to take a gift does not offend the giver. One who declines an invitation to eat offends the host, i.e. it is not proper for me to eat by you. Therefore, he intended to urge, not for a vow. If one vowed about taking a gift, perhaps he intended for a real vow.

Rebuttal (Taz 34): The Levush did not see the Gemara, which answered that this is not urging because he can say 'I am not a dog (or king).' The Rosh explains that if he requests such a big gift now, presumably he has been taking big gifts until now.

Defense (Nekudas ha'Kesef): The Levush saw the Gemara. He asked the Ran's question (24a DH Yeser), why doesn't R. Eliezer ben Yakov agree that he intended for a real vow? He answered by distinguishing between gifts and eating. The Rambam, Tur and Shulchan Aruch do not specify that it is only of he has been taking gifts until now.

Shulchan Aruch (ibid.): Similarly, if Reuven said to Shimon 'you may not benefit from me if you will not give to me such and such', Reuven can permit this without a Chacham. He says to him 'it is as if I received.'

Beis Yosef (DH v'Od, citing R. Yerucham): In the Reisha, Reuven normally benefits from Shimon, so it is as if he said 'I am not a dog', and it is not a vow of urging. In the Seifa, Shimon normally benefits from Reuven, so it is as if he said 'I am not a king.'

Rema: Some say that only regarding doing an action, he can say 'it is as if you did it', but if he said 'my property is Konam to you if you will go to the place Ploni', he cannot say 'it is as if you did not go.' Some do not distinguish; whenever a condition is for the Noder's benefit, he can say 'it is as if you fulfilled it.'

Source (Ran 24a DH Hareini): The Rashba says that only regarding doing an action, he can say 'it is as if I received', for even if he received he could return it. There is no need to transfer back and forth. One cannot say so to negate an action, e.g. it is as if you did not go there. Some say that in either case he intended for his own desire, and now that he is not concerned, his desire was fulfilled.

Rema (ibid.): If Reuven told Shimon 'you may not benefit from me if you will not give to my son David such and such, if David eats by his father, the vow was for Reuven's benefit, so he can permit it by saying 'it is as if I received.' If not, the vow was David's, so only he can permit it by saying 'it is as if I received.'

Source: Ran (ibid.)