The Gemara answers: Rabbi Yitzḥak stated his opinion in accordance with the opinion of Rabbi Eliezer ben Ya’akov, as it is taught in a baraita (Tosefta, Shevuot 5:10) that Rabbi Eliezer ben Ya’akov says: There are times when a person takes an oath about his own claim. How so? One says to another: One hundred dinars of your deceased father’s was in my possession, as I had borrowed that sum from him. And I already paid him part [peras] of it, but I still owe you fifty dinars. In this case, he is not believed unless he takes an oath that he repaid the half, like anyone who admits to part of a claim. And this is an example of a case where one takes an oath about his own claim. Although nobody has claimed anything from him, he still takes an oath on the basis of his own statement.

But the Rabbis say: In such a case, the borrower is regarded only as someone who is returning a lost item, and therefore he is exempt from an oath. Rabbi Yitzḥak’s position is similar to that of Rabbi Eliezer ben Ya’akov. Since the finder says that he found only half of what the owner claims was lost, he is treated like someone who admits to part of a claim and therefore takes an oath.

The Gemara asks: But does Rabbi Eliezer ben Ya’akov not maintain that someone who returns a lost item is exempt from an oath? Rav says: The case in dispute between Rabbi Eliezer ben Ya’akov and the Rabbis is not one where nobody has claimed anything from the borrower, as in such a case all agree that the borrower is exempt from taking an oath. Rather, it is a case where the creditor has died, leaving a child as his heir, and this minor confronts the borrower and claims a hundred dinars from him, which he alleges was lent by his late father. The other admits to having borrowed the money but claims that he already repaid half the sum. Since he admits to part of the claim, he takes an oath that he did repay the other part.

The Gemara asks: Does the claim of a minor have any substance? But didn’t we learn in a mishna (Shevuot 38b): One does not take an oath in response to the claim of a deaf-mute, an imbecile, or a minor, as the claim of one who lacks halakhic competence has no significance whatsoever. According to this, if a minor brought a claim against the borrower, it is as though there were no claim at all but only the borrower’s admission, and so the borrower should be exempt from taking an oath.

The Gemara answers: To which kind of minor was Rav referring? It was to an adult son of the creditor. And why does Rav call him a minor, if he is in fact an adult? It is as with regard to his father’s affairs he is like a minor. He does not know with certainty how much money the borrower repaid but merely says that he thinks he owes his father more.

The Gemara asks: If that is so, that we are dealing with a case where the deceased creditor’s adult son made a claim against the debtor, how can Rabbi Eliezer ben Ya’akov say about this claim that it is his own claim? Is this an oath taken about his own claim? It is an oath taken about the claim of others, i.e., the son. The Gemara answers: Rabbi Eliezer ben Ya’akov calls it an oath taken about one’s own claim, although it is really the claim of others, because it is his own admission that obligates him to take the oath.

The Gemara objects: All claims that lead to the oath of one who admits to part of the claim are also a combination of the claim of others and the defendant’s own admission. Rather, Rabbi Eliezer ben Ya’akov and the Rabbis disagree with regard to the following explanation given by Rabba, as Rabba says: For what reason did the Torah say that one who admits to part of the claim brought against him takes an oath with regard to the rest of the claim, which he denies, whereas one who denies the entire claim is not required to take an oath? Rabba answers: The oath of partial admission is based on a presumption with regard to the defendant’s behavior. There is a presumption that a person would not be so brazen as to stand before his creditor and deny his debt when his creditor knows that he is lying.

Rabba continues: And this one who admits to part of the claim would want to deny all of it, and the only reason he does not deny all of it is because a person would not be so brazen before his creditor. And in fact, he would want to admit to all of the claim to him. And the reason that he did not admit the whole claim to him and say that in fact he owes him the entire sum is that he was evading his obligation temporarily. The debtor is short of money and he thinks: I will pay my creditor as much as I can afford now, and I will evade paying the rest until I have enough money, and then I will repay him the rest, to which I have not yet admitted. Therefore, the Merciful One states: Impose an oath on the debtor in order to induce him to admit all of the debt to the creditor.

Following Rabba’s reasoning, the difference of opinion between Rabbi Eliezer ben Ya’akov and the Rabbis can be explained as follows: Rabbi Eliezer ben Ya’akov holds that there is no difference between the creditor himself and the creditor’s son, as in all cases the debtor would not be so brazen as to deny his debt. Therefore, the debtor is not considered like someone who is returning a lost item. Rabbi Eliezer ben Ya’akov maintains that Rabba’s reasoning applies in this case as well, so he is required to take an oath. And the Rabbis hold that he would not be so brazen as to deny a debt before the creditor himself, but toward his creditor’s son he would be brazen and deny the claim completely. And since he was not so brazen as to deny the entire claim, but admitted to part of it, he is considered like someone returning a lost item, and therefore he is exempt from taking an oath.