Shevuos, Chapter 6, Mishnah 6. This Mishnah deals with the question of a partial admission (modeh b'miktzat): do we have before us a valid partial admission that obligates an oath, or a total denial?
Two introductions before we begin:
The law of a pledge: One who lends money to his fellow and takes an object as a pledge is considered a paid guardian over that pledge. Therefore, if the pledge is lost or stolen, the lender must pay for it. In all the cases in our Mishnah the pledge was lost, and the lender, under whose guard the pledge was held, bears responsibility for it.
The coinage system: A sela consists of two shekels, and each shekel consists of two dinars, so there are four dinars in a sela.
The first case - the lender's claim, and the borrower denies everything:
The Mishnah opens: "HaMalveh es chaveiro al hamashkon v'avad hamashkon" - a loan that was given on the basis of a pledge, and the pledge was lost while in the lender's possession. "Amar lo: sela hilvisicha alav v'shekel hayah shaveh" - the lender claims: I lent you a sela on the basis of this pledge, and the pledge was worth only a shekel, half the value of the loan, and therefore you still owe me a shekel. "V'halah omer: lo chi, ela sela hilvisani alav" - the borrower responds: it is true that you lent me a sela on this pledge, but the pledge was worth a full sela. Since responsibility for the pledge rested upon you and you lost it, and its value equals the amount of the loan, I owe you nothing.
Since the borrower denies the entire claim and asserts that he owes nothing at all, he is exempt from an oath, for there is no partial admission here. It is worth noting that in the time of the Gemara the Sages instituted that one who denies an entire claim must swear a shevuas heses, but this enactment did not yet exist in the time of the Mishnah.
The second case - the borrower makes a partial admission:
The Mishnah continues with a similar case: the lender claims "Sela hilvisicha alav v'shekel hayah shaveh", and as in the previous case he is demanding a full shekel. "V'halah omer: lo chi, ela sela hilvisani alav u'sheloshah dinarim hayah shaveh" - the borrower admits that he did indeed receive a sela, but according to him the pledge was worth three dinars and not two dinars (which equal a shekel). The result is that the lender is claiming a full shekel while the borrower admits to only one dinar. Since he admits to part of the claim, he is obligated to swear.
The third case - the borrower's claim, and the lender denies everything:
The next case reverses the roles, and now it is the borrower who is making the claim: you lent me a sela on the basis of this pledge, but the pledge was worth more than the loan, it was worth two selas. Since you lost it, the sela I borrowed from you is automatically repaid through your responsibility, and you still owe me an additional sela. The lender, who bore responsibility for the pledge, responds: not so, it was worth only the amount of the loan, and I owe you nothing. Since he denies the entire claim, he is exempt from an oath.
The fourth case - the lender makes a partial admission:
The borrower claims as in the previous case: you lent me a sela on this pledge, and the pledge was worth double, and therefore you owe me an additional sela. The lender responds: it is true that I lent you a sela on this pledge, and it is true that it was worth more than a sela, but it was worth only five dinars, and therefore I owe you only one dinar. In other words: I lost the pledge, and you owed me a sela, so I owe you only one dinar, which is the difference between the value of the pledge and the value of the loan. Since the lender admits to part of the claim, he is obligated to swear.
The oath of the holder regarding the loss of the collateral:
Until now we have been dealing with the oath of one who admits to part of a claim, but there is another factor to take into account: the one holding the collateral, namely the lender, whether he is the one who admits to part of the claim or whether the other party is, since he claims that the collateral was lost - he must swear that the collateral is no longer in his possession and that he spoke truthfully about its loss. Why is this necessary? Because perhaps the collateral appeals to him and he wants it for himself, and he has no difficulty paying its value and keeping it. Therefore he is required to swear that it was indeed lost.
Who swears first?
Once a situation arises in which the lender must swear that the item is not in his possession, and the borrower must swear as one who admits to part of the claim, the Mishnah clarifies which of the two swears first: "U'mi nishba? Mi shehapikadon etzlo" - the one holding the deposit, namely the lender, swears first.
And the reason is: "Shema yishava zeh v'yotzi halah es hapikadon" - if the borrower were to swear first as one who admits to part of the claim, the lender, who claimed that the deposit was lost and perhaps it was never lost at all, might produce the collateral and display it in order to refute the borrower's oath and prove that its value is as he said and not as his fellow said. It would turn out that a person swore falsely before us, and a desecration of Hashem's Name results from this.
In summary: In this Mishnah we learned four cases of a dispute between a lender and a borrower over the value of a collateral that was lost: in two of them the defendant denies the entire claim and is exempt from an oath, and in two he admits to part of the claim and is obligated to swear. We further learned that the one holding the collateral must swear that it is not in his possession, and that he is the one who swears first - lest his fellow swear and afterward he produce the deposit, and Heaven's Name be desecrated.