Gemara

61b (Rav Nachman): If one sold a house in a big Birah (building), even if he gave boundaries of the entire Birah, he merely gave boundaries that people recognize.

Question: If people call the house a house, and the Birah a Birah, this is obvious! If people call also the Birah a house, he sold the whole Birah!

Answer: Most call the house a house, and the Birah a Birah. Some call also the Birah a house. One might have thought that he sold the whole Birah. Rav Nachman teaches that this is not so. Had he sold it, he would have written 'I do not omit anything from this sale.'

77b (Mishnah): If one sold a yoke, he did not sell the oxen. If he sold the oxen, he did not sell the yoke;

R. Yehudah says, the price indicates whether or not he sold the oxen. If he sold a yoke for 200 Zuz, surely this includes the oxen!

Chachamim say, the price is not a proof.

Question: What is the case? If people call a yoke (only) a yoke, and call oxen (only) oxen, obviously, the oxen are not sold!

Answer: Rather, they call a yoke a yoke, and call oxen oxen, and some use 'yoke' to refer to the oxen as well. R. Yehudah holds that the price indicates what he sold. Chachamim hold that the price is not a proof.

Question: If the price is not a proof, the sale should be invalid!

Answer #1: Indeed, Chachamim mean that the sale is invalid.

Answer #2: Chachamim say that Ona'ah (returning the overcharge) and voiding of the sale apply in a case in which one could err. If clearly he knew that the price is too high, he gave the extra money for a gift.

92a (Rav): If Reuven sold an ox to Shimon, and it was found to be a gorer, it is a Mekach Ta'os (a mistaken sale; it is void).

(Shmuel): Reuven can say 'I sold it to you for slaughter.'

Question: Let us see whether Shimon buys oxen for plowing or for slaughter!

Answer: The case is, he buys for both.

Question: Let us see whether the price was of a plowing ox or an ox for slaughter!

Rishonim

Rambam (Hilchos Mechirah 27:2): If one sells a yoke, he did not sell the oxen. If he sold the oxen, he did not sell the yoke, even in a place where some call a yoke 'oxen.'

Rambam (5): The price is not a proof. If he erred a plausible amount, Ona'ah and Bitul Mekach apply like in any sale. If he erred an implausible amount, there is no Bitul Mekach, for he gave a gift. The price is not a proof.

Hagahos Maimoniyos (3): This is not difficult for Rav, who says (Kidushin 46b) that if one was Mekadesh his sister, the money is a deposit. There, the Kidushin is totally Batel. Here, the sale is valid. It is unreasonable that the seller keep the value of the yoke and return the rest.

Rosh (6:2): Chachamim agree that the price is a proof when it does not contradict the primary way people speak.

Tosfos (92a DH v'LIchzi): Chachamim hold that the price is not a proof only when the majority (of how people speak) and Chazakah (he has the money) favor the seller. Even according to texts that say (on 77b) 'some call a yoke a yoke... and some...' (there is no majority), the price is not a proof because the Chazakah favors the seller. If there is a majority (e.g. most buy cows for plowing) against a Chazakah, the price determines what was sold.

Rashbam (92a DH v'LIchzi): Chachamim hold that the price is not a proof only when not everyone calls oxen 'yoke'. The seller can say that the buyer calls oxen oxen, and he sold only a yoke. Ha'Motzi mi'Chavero Alav ha'Re'ayah; since the buyer cannot prove how he speaks, he gets only a yoke. Here, we know that the buyer ofen buys for plowing and Shechitah, therefore, the price is a proof. Also above, if everyone calls also oxen 'yoke', even if they sometimes call them oxen, the price is a proof, for we know that the buyer often calls them yoke.

Tosfos (61b DH Ela): The Rivam says that if everyone calls the Birah a house, and when they mean just the house they specify, one who bought a house receives the entire Birah even without a proof (from the borders). The Ri explains that if everyone calls also the Birah a house, even though they call also the house a house, the boundaries proves that he sold the whole Birah. Rather, some do not call the Birah a house, therefore the boundaries are not a proof.

Poskim

Shulchan Aruch (CM 220:4): If one sells a yoke, he did not sell the oxen. If he sold the oxen, he did not sell the yoke, even in a place where (Rema - some) call a yoke 'oxen.'

SMA (10): Also the Rambam and Rema (Sa'if 8) discuss where they call a yoke 'oxen.' If this is not a printing mistake, we must say that this refers to 'if he sold the oxen, he did not sell the yoke.' However, in Sa'if 8 the Rema says 'if everyone calls a yoke 'oxen', and when they mean just a yoke they say 'a yoke alone', then even without a proof from the price, everything is sold.' This shows that he discusses whether oxen are included with a sale of a yoke. Therefore, it seems that the text should say 'where they call oxen 'yoke'. This applies also in the Tur. When everyone calls a yoke 'oxen' and vice-versa, even without a proof from the price, all agree that he sold according to how people speak, like it says in Bava Basra (61b).

Gra (5): The Shulchan Aruch is like the Rif's text.

Shulchan Aruch (8): In all these cases, the price is not a proof. If he erred a plausible amount, Ona'ah and Bitul Mekach apply like in any sale. If he erred more than a plausible amount, there is no Bitul Mekach, for he gave a gift.

Beis Yosef (DH u'Mah): The Rashbam says that the first answer (Chachamim say the price is not a proof, i.e. the sale is invalid) is weak. Presumably, the Halachah follows the latter answer. The Ran says that the Halachah follows the latter answer, and that the Rashbam and Ramban agree, and it seems that also the Rif agrees, for he brought both versions Stam. I am astounded by R. Chananel. In the next Perek he says that the price is not a proof, and it is Bitul Mekach, i.e. like the first answer. The Tur says that Rav Hai Gaon holds that the price proves that there is Bitul Mekach, for he rules like the first answer. The Tur says that the Rosh rules like the Rashbam, even though the Rosh did not explicitly say so. Since the Rosh brought both answers Stam, this connotes that the rules like the latter, like the Ran said about the Rif. The Ran says that the price is not a proof even if the buyer was Mioshech the yoke and oxen and he still has the money, for when we say 'he did not sell', this is not due to Safek. Rather, this is the Halachah. Also the Ramban says so.

Rema: This is only in a place where where people call oxen oxen and they call a yoke a yoke, but if most call a yoke 'oxen', then we say that the price indicates what he sold. If everyone calls a yoke 'oxen', and when they mean just a yoke they say 'a yoke alone', then even without a proof from the price, everything is sold.

Beis Yosef (DH v'Ela): If everyone calls also oxen 'yoke', and the price was appropriate for oxen, all agree that the price is a proof. The seller should have specified if he sells only the yoke. Since he did not, we say that he sold everything.

Beis Yosef (DH v'Afilu): The Tur says that the Ramah holds that even if only the majority call a yoke 'oxen' the the price is a proof, unlike the Rashbam, who says that the the price is a proof only when everyone speaks this way. Really, the Tur means that the majority call oxen 'yoke'.

Gra (11): 'They call a yoke a yoke, and call oxen oxen, and some...' connotes that the majority speak the first way. This is like Tosfos 92a. The Rashbam and Rosh hold that the price is a proof when everyone calls oxen yoke, but they also call a yoke yoke without specifying. This is like the Ri in Tosfos 61b. The Rema and Ramah are like the Rivam in that Tosfos.

Rema: Some say that one who sold oxen did not sell the yoke Stam, for we can say that he sold them for Shechitah. If he specified that they are for plowing, the yoke is sold with the oxen.