Gemara

(Mishnah): We divide a Chatzer only if each partner will get four Amos, and a field only if each will get enough area to sow nine Kavim. We divide a salon, small tower, dovecote, garment, bathhouse, olivepress, or Beis ha'Shelachin (an irrigated field) only if each will get enough (to be called this). The rule is, we divide only if each will get a portion that keeps the original name.

All these laws are when only one partner wants to divide. If both want to divide, they may always do so;

13a - Question: If it (a Chatzer, field...) is too small for each partner to get a proper share (that keeps its name), what is the law?

Answer #1 (Rav Yehudah): 'Gud O Agud' applies. (A partner can set a price and say 'buy my share for this price, or I will buy your share for this price.')

Answer #2 (Rav Nachman): 'Gud O Agud' does not apply.

Question (against Rav Nachman - Mishnah): The rule is, we divide only if each will get enough. If not, we estimate its value (and apply Gud O Agud).

Answer: Tana'im argue about whether or not we apply Gud O Agud:

(Beraisa): Levi may tell his partner Yehudah 'take a proper share, and I will take (the rest, even though it is) less than this;

R. Shimon ben Gamliel says, Yehudah can protest.

Question: If we understand the Beraisa simply, what is R. Shimon's reason?!

Answer #1: Rather, the Beraisa is abbreviated. It means as follows: Levi can say 'take a proper share, and I will take less.' Also, Levi can say 'Gud O Agud'. R. Shimon ben Gamliel says, he cannot say 'Gud O Agud.'

Rejection (and Answer #2): The Beraisa is like the simple reading. R. Shimon says that Yehudah can protest 'I have no money to compensate you for the larger portion, nor do I want to take it for a gift - "v'Sonei Matanos Yichyeh"!'

Rishonim

Rif (8b) The Halachah follows R. Shimon ben Gamliel, for his reasoning is proper.

Rosh (1:50): R. Chananel says that some say that the Halachah follows the first Tana who argues with R. Shimon ben Gamliel. Since we follow a majority against an individual, our own reasoning should not override this.

Shach (CM 171:9): The Rif (Bava Basra 81a) holds that the rule that the Halachah always follows R. Shimon ben Gamliel in the Mishnah (with only three exceptions) is only when there is a reason. This is why he needed to say that his reasoning is proper. Tosfos (Bava Metzia 69a DH Ela) holds that this rule applies even to Beraisos, and only to Mishnayos.

Rebuttal #1 (Hagahos ha'Gra Bava Metzia 69a 6): The Rif (Bava Basra 81a) teaches that the Halachah does not follow this rule (therefore, we rule like R. Shimon ben Gamliel only if there is a reason).

Rebuttal #2 (R. Akiva Eiger): The Nimukei Yosef (63b DH Aval) says that even though the rule 'R. Eliezer ben Yakov's teachings are clean' (the Halachah follows always him) is even in Beraisos, the rule 'the Halachah always follows R. Shimon ben Gamliel b'Masnisin...' is only for Mishnayos. Shabbos 21a supports this.

Note: In Shabbos 21a, Rabah assumes that the Halachah follows the first Tana against R. Shimon ben Gamliel in a Beraisa. Abaye said that we follow R. Shimon ben Gamliel, for his opinion was followed in practice. The Shach said that the Rif holds that the rule applies only when there is a reason! Perhaps R. Akiva Eiger brings a proof from other Rishonim (who do not require a reason) that the rule applies only to Mishnayos.

Rambam (Hilchos Shechenim 1:5): If there is not enough for each to get a proper share, and Levi said 'let us divide this way. Even though the shares are unequal, I will take the smaller, and you will take the bigger', we do not heed him. Yehudah can say 'I do not want to take a gift.' Rather, since the law is that we do not divide it, we evaluate it (and Yehudah buys or sells all of it).

Question (Lechem Mishneh): The Gemara said that he cannot force one who has no money to take a gift. The Rambam discusses when Yehudah has money (for he concludes that we evaluate it). If so, why can Yehudah say 'I do not want to take a gift'? If he does not want a gift, he can buy it!

Answer (Merkeves ha'Mishnah): Indeed, if Yehudah offered to buy a share, he cannot refuse to pay and refuse to take a gift. In the Beraisa, he said 'I agree to spend money only for all of it, but not just for a share.'

Rosh (ibid): The Gemara challenged R. Shimon ben Gamliel, and needed to say that the Beraisa is abbreviated, for it was unreasonable that he would argue with the first Tana. The Gemara gave a weak answer. It is totally unreasonable that the Halachah follows this. If he said 'take a Shi'ur (of the object) for money (pay me its value above what will remain for me' we do not heed him. This is like one who can sell, but cannot buy (for he demands to receive money). Also if he 'take a Shi'ur for money, and I will take (what remains, which is) less than a Shi'ur', or 'you take less, and I will take a Shi'ur' we do not heed him. This is unlike Gud O Agud, for there both choices are proper and fair to both. Offering 'take less' is improper, for less than a Shi'ur is useless.

Rosh: R. Yonah says that if he offered 'take a Shi'ur for money, and I will take less, or I will (Piplulei Charifta 1 - take a Shi'ur for money, and you will take less, or I will) take everything for money', even though he does not give to his partner an option to buy everything, we heed him. Had he said 'take everything for money, or I will take everything for money', we would heed him. Now also that he offered 'take a Shi'ur for money', we heed him, for he can say 'if you want to buy from my portion, buy until you have a Shi'ur. That suffices for you. Why must you buy my entire portion? If you do not want to buy, I will buy everything. If you want, you may keep less than a Shi'ur.'

Ramban (13b DH v'Gud, brought in Beis Yosef CM 171 DH v'Chosav): Rashi explains that the first Tana holds that one may say Gud O Agud, i.e. he does not pardon anything. Buy my share, or I will buy yours. It seems that he holds that if one said 'take three Amos (in the Chatzer), and I will (take the remaining four and) give compensation (money) to you, or take four and give money to me', this is Gud O Agud. Some disagree, for three if useless. He can say 'I do not have money, and I do not want to split, for three is not suitable for living.' This is proper reasoning.

Magid Mishneh (Hilchos Shechenim 1:5): Some (explain like R. Yonah, and) say that Gud O Agud is even when the entire matter is too small to be useful. The Ramban agrees.

Poskim

Shulchan Aruch (CM 171:10): If the law is that something is not divided (for it is too small), and one said 'let us make two shares. One is a proper size, and the other is small. I will take the smaller, and you will take the bigger', and pay me its value above the smaller, he cannot force his partner. Even if he says 'take the bigger share for a gift', the other can say 'I do not want to take a gift.' Some disagree.

Beis Yosef (DH Ela): The Beraisa supports Rav Yehudah. The Gemara said that Tana'im argue about this to be Docheh, but this is not really so.

Beis Yosef (DH v'Chosav): The Mordechai (509) says that R. Chananel rules like the first Tana regarding a gift (when he offers 'take the bigger share for free), but not for a sale (when he demands compensation for it), for Gud O Agud does not apply when the buyer does not get something useful. The first Tana says that we heed him only regarding a gift. Ba'al ha'Itur rules like the first Tana even regarding a sale. He explains that R. Shimon ben Gamliel disagrees (about a sale) because he disagrees with Gud O Agud. Since we conclude that Gud O Agud applies, the Halachah follows the first Tana. Also Rabbeinu Meir rules like the first Tana.

SMA (24): Those who disagree hold that "v'Sonei Matanos Yichyeh" does not apply when the giver wants to give to help himself.

Shulchan Aruch (ibid): If he said 'take the bigger share for its value, and I will take the smaller, or I will take the bigger for its value, and you will take the smaller, and if you do not want the small, I will buy everything', we heed him, even though he does not give his partner an option to buy everything.

SMA (23): All agree in this case.

Beis Yosef (DH v'Nimtza): If he said 'take the bigger share for its value, and I will take the smaller, or I will take the bigger for its value, and you will take the smaller' (without offering to buy everything), only Rashi says that the partner must accept one of these.