1) ANNULLING A DEBT WHICH IS NOT IN ONE'S POSSESSION
QUESTION: The Gemara teaches that a lender may forgive a loan after he sells the contract of debt to a third party: Reuven, who loaned money to Shimon, sells the Shtar Chov (contract of debt) to Levi. Reuven may be Mochel (forgive) the debt even after the Shtar is purchased by Levi, and consequently Shimon does not have to pay Levi. (The Gemara on 86a discusses whether or not Reuven must reimburse Levi.)
Why is a person permitted to forgive a loan which he has already sold and which is no longer in his possession?
(a) RABEINU CHANANEL (cited anonymously by the RIF, and identified by the Ran as Rabeinu Chananel) explains that the person who sells the Shtar Chov may cancel the debt even after its sale since he is may claim that he checked his records and found that the debt was already paid, or that he is unsure whether or not the debt was already paid.
The Rif and others reject this approach for a number of reasons. The Gemara's wording implies that the creditor did not say that the debt was paid, but that he forgives the debt. If he agrees that the debt was not paid, why may he cancel the debt which is no longer in his possession?
Even if the creditor admits that the debt was paid, how can that admission prevent the buyer of the debt from collecting it? The Gemara earlier (19a) teaches that a person's own admission is not accepted if it causes a loss to others. In this case, the seller should not be able to cause the buyer of the debt a loss by "admitting" that there is no longer any debt.
(b) TOSFOS (DH ha'Mocher) in the name of the RI explains that mid'Oraisa a person may not sell a loan because it is not an object upon which a Kinyan can be made.
It is true that if the borrower owns property, there may be a Shibud (lien) placed upon the real estate. A lien constitutes a partial Kinyan, and thus it is something which the lender may sell. If, however, the borrower has no real estate, the lender has nothing of the borrower's to sell since there is no such thing as a lien on movable property (Metaltelin). Therefore, the sale is not valid mid'Oraisa. It is only a Takanah d'Rabanan that allows a person to sell a loan.
Since mid'Oraisa the debt still belongs to Reuven, he is able to forgive it. The Mechilah, which is mid'Oraisa, uproots the sale of the loan since the sale is only mid'Rabanan.
Would the Ri maintain that one cannot forgive a debt he has sold if the borrower owns land? The Ri does not differentiate between whether the borrower actually owned land at the time of the sale or not. It seems that since the lender intends to sell the loan alone (and not the Shibud) when the borrower has no land and there is no Shibud to sell, so, too, anytime the lender sells a loan his intention is to sell only the loan and not the Shibud (even when the borrower does own land).
Tosfos points out that according to this reasoning, if a loan is transferred in a manner that works mid'Oraisa, the lender cannot forgive the loan once it is no longer in his possession. Transfers that work mid'Oraisa include, according to various opinions, a Matnas Shechiv Mera (the gift of a dying person; see Bava Basra 147b, as cited by Tosfos here), a case of Shibuda d'Rebbi Nasan (where Reuven borrowed money from Levi before he lent money to Shimon, he may transfer his loan to his own creditor; see Kesuvos 19a and Tosfos there, DH u'Chegon), and Ma'amad Shelashtan (where the lender transfers the loan in the presence of the borrower; see Gitin 13b and Tosfos there).
(c) Tosfos here writes that RABEINU TAM also rules that the sale of a loan is mid'Rabanan. However, Rabeinu Tam later retracted his view (according to the TOSFOS SHANTZ) and decided that the sale of a loan is valid mid'Oraisa. Why, then, may the lender forgive the loan that is no longer in his possession?
The ROSH (9:10), RAN, and other Rishonim write in the name of Rabeinu Tam that the original lender may forgive the loan for a different reason. A loan creates two different Shibudim (obligations) upon the borrower. The first is a "Shibud ha'Guf" -- the borrower becomes personally obligated to repay the loan that was given to him. It is a personal obligation to which the Gemara (86a) refers when it says, "Peri'as Ba'al Chov Mitzvah" (the repayment to a creditor is a Mitzvas Aseh). The lender cannot sell this part of the loan.
The second Shibud, besides the Shibud ha'Guf, is that the borrower's property becomes collateral to the lender so that the lender has the right to collect from any assets that the borrower owns at the time the loan comes due, whether that property is land or mobile property -- the only requirement is that it be in the borrower's possession (i.e. he has not sold it). (Rabeinu Tam calls this a "Shibud Nechasim," even though the words "Shibud Nechasim" usually refer to another type of Shibud (a Shibud which allows a person to collect from land even after it has left the borrower's possession, and which does not take effect on mobile property). The right to collect from the borrower's possessions is based on the principle that "a person's possessions are his guarantors" (Bava Basra 174a). His possessions "take responsibility," so to speak, for the repayment of any loans which the person himself fails to repay.
This second Shibud -- the right to collect from the property of the borrower -- is transferable. This Shibud is what the lender sells, and the sale is valid mid'Oraisa. However, if the lender forgives the loan after the sale, first Shibud (the Shibud ha'Guf) which the lender did not sell (since it is not transferable) becomes annulled. Once there is no longer a Shibud ha'Guf on the borrower, the Shibud ha'Nechasim is annulled as well, since the borrower's property is no longer obligated to repay the loan for him if his loan has been annulled. That is why the buyer of the Shtar may no longer collect the debt.