GEMARA

38b (Mishnah): If Reuven claimed wheat, and Shimon admitted that he owes barley, Shimon is exempt;

Raban Gamliel obligates

40a (Rav Anan citing Shmuel): If Reuven claimed wheat, and Shimon admitted that he owes barley, if he rushed to admit for he sensed that Reuven was about to claim barley as well, Shimon must swear. If not, he is exempt.

Bava Kama 35b (Mishnah): If one of Reuven's two oxen damaged Levi's ox, and Levi says 'the Mu'ad damaged', and Reuven says 'no, the Tam damaged', ha'Motzi me'Chaveiro Alav ha'Re'ayah (the one who wants to collect must bring a proof).

Question: If Levi cannot bring proof, he collects like Reuven says. This refutes Rabah bar Nasan!

(Rabah bar Nasan): If Reuven claimed that Shimon owes him wheat, and Shimon admitted that he owes barley, Shimon is exempt.

Answer (Rav Papa): In the Mishnah one party is definite, and the other is unsure.

Question: If the damager is unsure and the victim is definite, this still refutes Rabah bar Nasan!

Answer: Rather, the damager is definite, and the victim is unsure.

Question: The Mishnah of wheat and barley teaches Rabah's law!

Answer: One might have thought that he is exempt from paying wheat, but he pays barley. Rabah bar Nasan teaches that he is totally exempt.

Question (Mishnah): If Reuven's two oxen damaged... Levi says that the Mu'ad (or big) ox damaged the big ox and the Tam (or small) ox damaged the small ox, and Reuven says oppositely, ha'Motzi me'Chaveiro Alav ha'Re'ayah.

(Inference): Without a proof, he collects like Reuven says.

Answer: Rather, if Levi cannot bring proof, he should collect like Reuven says, but he does not collect at all.

Question (Beraisa): Levi collects for the small ox from the Mu'ad, and for the big ox from the Tam.

Answer: That is when Levi seized the damager.

RISHONIM

Rif and Rosh (Shevuos 6:7): If Reuven claimed wheat, and Shimon admitted that he owes barley, if he schemed, i.e. rushed to admit because he sensed that Reuven was about to claim barley as well, Shimon must swear mid'Oraisa. If he did so innocently, he is exempt.

Rosh: If he schemed, it is as if Reuven already claimed also the barley, and Shimon admitted to it. If he said so innocently, even if Reuven claimed barley Toch Kedei Dibur of the admission, he is exempt. Modeh b'Miktzas is only when he admitted after the claim.

Rambam (Hilchos To'en 3:11): If Reuven began and claimed wheat, and before he finished speaking Shimon said 'I owe you only barley', if it looks to the judges that he schemed, he must swear. If he did so innocently, he is exempt.

Rambam (Hilchos Nizkei Mamon 9:10): If there was no clear proof which animal damaged, but witnesses testify that one of them damaged, the damager pays based on what he says happened. If the victim says 'you know Vadai that the bigger one damaged, the damager swears mid'Oraisa, for he partially admitted.

Rambam (11): If Reuven's two oxen damaged, and Levi says that the Mu'ad (or big) ox damaged the big ox and the Tam (or small) ox damaged the small ox, and Reuven says oppositely, ha'Motzi me'Chaveiro Alav ha'Re'ayah. If there was no clear proof, he is exempt. This is like one who claimed wheat, and the other admitted to barley. He swears Heses, and he is exempt. If Levi seized, he is paid for the big ox from the big and for the small for the small.

Magid Mishneh: We must say that there are no witnesses, for when there are witnesses, he pays (Halachah 10)! He is exempt for the Tam, for it is a Kenas (fine), which only witnesses obligate. He is exempt for the Mu'ad, for the admission was unlike the claim. The Rambam holds like the Ra'avad, that if a victim seized half-damage, he keeps it, unlike other fines.

Rebuttal (Gra CM 88:23): The Magid Mishneh's answers are poor. 'If there was no clear proof' connotes that there was some proof. The Rashba asked that witnesses who are unsure do not obligate. Rather, the Sugya is like the opinion that half-damage is not a Kenas.

Rosh (Bava Kama 3:15): Rashi and Tosfos say that Rabah exempts even from paying for barley, for Reuven says that he did not give barley; he pardoned it. This is astounding. Often, one has several claims against someone, but he does not want to claim all of them at once! The fact that he claimed one does not show that he pardoned the others! Also, what was the challenge against Rabah from the Mishnah of oxen? The Mishnah is not due to pardon! Rather, Rabah discusses a case like the Mishnah. Reuven claims 'I lent to you wheat on this day at this time', and Shimon says 'it was barley.' If Reuven lent both of them, he would have claimed both, since they were together. Rather, he admitted that he did not lend barley.

Rosh: The Ramah says that he is exempt from barley not due to admission, rather, because Shimon's admission does not obligate. Admission, even in front of two, obligates only if he said 'you are witnesses against me.' Admission in front of Beis Din helps without saying this, but only if there was a claim against him. Therefore, if Reuven says 'give to me the barley that you admitted to', Shimon can say 'I was joking.' If he does not say 'I was joking', he must pay. I disagree. We asked from the Mishnah, which does not discuss joking!

Nimukei Yosef (Bava Kama 17a DH v'Kaima): Shimon is exempt when Reuven made a Vadai claim of wheat. If Reuven knew that he deposited grain with Shimon, and he is unsure which grain, even if he claimed wheat, an admission to barley is an admission like the claim.

Shach (CM 88:13): Bava Kama 35b proves this.

Question (Mordechai Bava Kama 40): Even if Shimon said that he does not know about wheat, he is exempt. Rashi says that since Reuven did not claim the barley, he pardoned it. However, the Yerushalmi says that Shimon did not make a real admission. He merely jested. R. Yakir challenged Rashi. In Bava Metzi'a, when two deposited with Ploni and each claims the larger amount, we (pay each the smaller amount, and) leave the rest until Eliyahu comes. Ploni says that he does not know. He should be exempt (i.e. keep the smaller Keli), like in the case of wheat and barley! R. Yosi says that even the smaller Kli is left until Eliyahu. We should say that the depositors pardoned it!

Answer (Mordechai): The Riva says that the depositors have no claim against Ploni, rather, against each other. We must say so to resolve this with the case of a borrower who knows that he owes 50, but is unsure about the rest of the claim. Since he cannot swear, he pays.

POSKIM

Shulchan Aruch (CM 88:12): If Reuven claimed wheat, and Shimon admitted to barley, he is exempt even from paying for barley. Some consider it as if he admitted that Shimon does not owe barley. Therefore, he is exempt even if there are witnesses about the barley. A litigant's admission is like 100 witnesses.

SMA (22): In any case he must swear Heses. This is no less than denial, for which one must swear Heses.

SMA (23): 'Some say' teaches unlike the Ramah, who exempts because Shimon can say that he was joking. If he did not say so, and all the more so if witnesses testify about the barley, he is liable. Even though the Rosh rejected Rashi and Tosfos, he agrees that Shimon is exempt due to pardon, just the Rosh holds that it is only when Shimon admits to barley given at the same time that Reuven claims that he gave wheat.

Question (Taz): Why did the Shulchan Aruch omit the Rambam's opinion, that when there are witnesses, Shimon is liable?

(Shach 15): In Siman 400:3, the Shulchan Aruch brings only the Rambam's opinion! Perhaps this is because there, the witnesses do not know which damaged, so they do not contradict him. If one claims wheat and witnesses say that he is owed wheat or barley, the defendant must pay at least barley. Reuven claims 'they testify about wheat, like I say. If you say that they testify about barley, pay me for the barley.' Here, it is as if he admitted that he did not lend barley. His admission overrides the witnesses. I explain the Shulchan Aruch, but I say that the Ramah's Perush is primary.

Gra (22): The Gemara exempts even though we must say that there are witnesses, for we hold that half-damage of a Tam is a Kenas (fine), so unless there are witnesses he is totally exempt.