Gemara

(Beraisa): If one said "Erki Alai" and died, his heirs are liable.

Inference: A Milveh Al Peh (a loan for which no document was written) can be collected from heirs.

Rejection: No. Erchin is unlike a regular Milveh Al Peh, for it is explicit in the Torah.

22a - Question: Initially, Rav Nachman never collected from orphans' property. What was the reason?

Answer #1 (Rav Papa): Paying a creditor is a Mitzvah, and minors are exempt from Mitzvos.

Answer #2 (Rav Huna brei d'Rav Yehoshua): Perhaps the father gave Tzrari (deposited money with his creditor, to ensure that the debt will be paid).

The Halachah follows Rav Huna brei d'Rav Yehoshua.

Bava Basra 175a (Mishnah): If Reuven lent Shimon and wrote a document, he can collect even from Meshubadim (property that the borrower sold after he borrowed);

A Milveh Al Peh is collected only from Bnei Chorin (property that the borrower still owns).

(Ula): Mid'Oraisa, a Milveh b'Shtar (a loan for which a document was written) or Milveh Al Peh is collected from Meshubadim.

This is because Shibud (the lien on a borrower's property to pay the loan) is mid'Oraisa.

Chachamim enacted that one may not collect a Milveh Al Peh from Meshubadim to protect buyers from losing.

(Rabah): Mid'Oraisa, even a Milveh b'Shtar is not collected from Meshubadim. Shibud is not Mid'Oraisa. Chachamim enacted to collect a Milveh b'Shtar from Meshubadim due to Ne'ilas Delet (lest people be dissuaded from lending).

(Rav Papa): The Halachah is, a Milveh Al Peh is collected from heirs, but not from buyers.

It is collected from heirs, due to Ne'ilas Delet;

It is not collected from buyers, because it has no Kol (people do not hear about it. Buyers had no way to know to beware.)

Kidushin 13b (Rav Papa): The Halachah is, a Milveh Al Peh can be collected from heirs, because Shibud is mid'Oraisa. It can not be collected from Meshubadim, because it has no Kol.

Bava Kama 14b (Mishnah): Shavah Kesef.

(Rabah bar Ula): This teaches that Beis Din collects only from something that can be acquired through money.

Objection: Also slaves and documents can be acquired through money!

Rishonim

Rif and Rosh (Bava Basra 82b and 10:49): The Halachah is that Shibud mid'Oraisa. Rav Papa, who is Basra, says so in Kidushin. Here, Rav Papa taught that a Milveh Al Peh is collected from heirs due to Ne'ilas Delet, but not from buyers, for it does not become known. He does not contradict himself. Here, 'we collect from heirs due to Ne'ilas Delet' does not mean that it is only an enactment. Rather, he explains why Chachamim left the Torah law in effect, and did not enact to protect buyers.

Rambam (Hilchos Malveh 11:4): A loan document can be collected from buyers, for it has a Kol. Mid'Oraisa, all the borrower's property is Meshubad to the lender.

Rosh (Bava Metzia 1:36): The Rif says that a Shtar Hakna'ah has a Kinyan in it. What difference does the Kinyan make? In any case there is a lien, for Shibud is mid'Oraisa!

Tosfos (176a DH Goveh): Here, Rav Papa explains according to everyone, i.e. whether Shibud is mid'Oraisa or mid'Rabanan. In Kidushin, Rav Papa said that Shibud is mid'Oraisa. We can say that Rav Papa himself said only that a Milveh Al Peh is collected from heirs, and the Gemara explained here according to the opinion that Shibud is mid'Rabanan, and there it explained according to the opinion that Shibud is mid'Oraisa. R. Eliyahu says that in Kidushin, Rav Papa rules that Shibud is mid'Oraisa regarding Korban, i.e. if a woman died, her heirs bring her Olah. R. Chananel connotes like this. This is primary.

Poskim

Shulchan Aruch (CM 39:1): One who lends with a document collects from Meshubadim.

Beis Yosef (DH ha'Malveh): The Gemara says that Shibud is mid'Oraisa.

Shach (2): The Beis Yosef said that this is because Shibud is mid'Oraisa. There is no Kol to a Milveh Al Peh, therefore the creditor cannot take sold land, lest buyers lose. Also the Levush says so. Really, Poskim argue about this. The Rif, Rambam and Semag hold that Shibud is mid'Oraisa. Tosfos in several places says that Shibud is not mid'Oraisa, and says that this is primary. Also the Mordechai, Sefer ha'Terumah in the name of the Ra'avad say so. (However, the Ra'avad on Hilchos Erchin 1:21 holds that Shibud is mid'Oraisa. Perhaps Sefer ha'Terumah refers to a different Ra'avad, or the Ra'avad retracted, or in Hilchos Erchin the Ra'avad was not particular about this; he came to argue with the Rambam about another matter.) Also Ba'al ha'Itur and Tosfos Rid hold like Tosfos.

Shach (2): The Rosh's opinion is unclear. In Bava Basra he connotes that Shibud is mid'Oraisa, and the Tur connotes that this is the Rosh's opinion. However, we learn from otherwise from his words in Bava Kama (1:14). He writes that a creditor does not collect from heirs' slaves, for the Halachah follows Rav Nachman, who says that slaves are like Metaltelim for all laws mid'Rabanan. Tosfos and the Rosh explain that it is mid'Rabanan because Shibud is not mid'Oraisa. In Bava Basra the Rosh merely cited the Rif. Often, the Rosh cites the Rif, and elsewhere he disagrees. In Bava Metzia, the Rosh asked 'in any case there is a lien, for Shibud is mid'Oraisa!' Do not infer that the Rosh holds that Shibud is mid'Oraisa. He questioned the Rif, who holds that Shibud is mid'Oraisa. In Gitin (5:2) the Rosh says 'even though we hold that Shibud is mid'Oraisa...' This is difficult. Perhaps he asks against that opinion. The Yam Shel Shlomo (Bava Kama 1:16) says that the Rosh clearly holds that Shibud is mid'Oraisa. He brought proofs for this. He did not discuss the proofs I brought against this. Also, why did the Yam Shel Shlomo himself rule that slaves are like Metaltelim regarding collecting debts, since this is only for mid'Rabanan laws!

Shach (2): A proof that Rav Papa holds in general that Shibud is not mid'Oraisa is that he holds that paying a creditor is a Mitzvah (and therefore, minors need not pay). Also, the Rif explains that Rav Papa said 'a Milveh Al Peh is collected from heirs due to Ne'ilas Delet' to explain why Chachamim left the Torah law in effect. Why must he give a reason for this?! The Tosfos Rid, Ritva, and Ben Lev rejected this answer of the Rif. Even the Ramban, who always defends the Rif as much as possible, rejected it. The Ramban and Ritva concluded that Rav Papa holds that elsewhere, Shibud is not mid'Oraisa. There is a clear proof of this regarding loans. He says that paying a creditor is a Mitzvah, and (minor) orphans are exempt from Mitzvos. If Shibud is mid'Oraisa, there is a lien on the property! Also, according to the Rif, why in Kidushin did Rav Papa explain his law due to Shibud mid'Oraisa, and in Bava Basra he said that it is due to Ne'ilas Delet? We must say like Tosfos. In Bava Basra Rav Papa discusses a Stam loan, so the Gemara needed to say that it is due to Ne'ilas Delet. In Kidushin he discusses a Milveh ha'Kesuvah b'Torah (an obligation that is explicit in the Torah), e.g. Chatas, Pidyon ha'Ben and damages, which are not common, so Ne'ilas Delet does not apply. Shibud is mid'Oraisa applies.

Question (Ketzos ha'Choshen 1 DH v'Kasheh): In Bava Kama, the Gemara asked that according to Rabah, there should be a Shibud on slaves to pay damages. If the Rosh agrees that Shibud is mid'Oraisa for damages, slaves are like land (for Torah laws), and indeed there is a Shibud!

Answer (Nesivos ha'Mishpat 2 DH uvi'Ketzos): In any case, what was the Gemara's question from slaves? Many Amora'im hold that creditors collect slaves even from orphans! Rather, the Gemara challenged Rav and Shmuel, who hold that Shibud is not mid'Oraisa even for a Milveh ha'Kesuvah b'Torah.

Shach (2): The Ramban and Ritva give another proof that we hold that Shibud is mid'Oraisa. We rule like Rav Huna, and unlike Rav Papa, who says that paying a creditor is a Mitzvah and minors are exempt from Mitzvos. The Nimukei Yosef (Bava Basra 81b) derives from here that Shibud is not mid'Oraisa. I do not understand this proof. Even Rav and Shmuel, who hold that Shibud is not mid'Oraisa, agree that one who has a document collects from heirs. Therefore, we needed to say that (regarding minors) we are concerned for Tzrari!

Gra (Likut): Tosfos answered that in Kidushin, Rav Papa taught (that a Milveh Al Peh is collected from heirs, but not from buyers) regarding a Milveh ha'Kesuvah b'Torah such as damages, Erchin... (Ne'ilas Delet does not apply to. It is like a Milveh b'Shtar regarding heirs, but not regarding buyers. Bava Basra discusses a Milveh Al Peh.) Tosfos needed to say (that a ruling of Beis Din is like a document) because Tosfos holds that Rav Papa discusses even a Milveh ha'Kesuvah b'Torah. The Rif can say that even according to the opinion that a Milveh ha'Kesuvah b'Torah is not like a Milveh b'Shtar, the heirs pay because Shibud is mid'Oraisa. Rav Papa said his law only regarding a Milveh (Al Peh), which has no Kol, but not for damages. R. Tam says (that Shibud is not mid'Oraisa, therefore also damages are not collected from buyers. Shibud was enacted only for a loan document). This is difficult for the opinion that Shibud is mid'Oraisa. (If so, damages should be collected from buyers!) The Rashba (Bava Kama 8a DH v'Ha) answered that damages are collected from Meshubadim after a ruling of Beis Din (this is like a document), or a Milveh ha'Kesuvah b'Torah is like a Milveh b'Shtar, or it is collected from buyers because Shibud is mid'Oraisa, and we hold like this. He brought a proof from Bava Kama 33b (which says that damages of an ox are collected from one who bought it). Tosfos answered that damages have a greater Kol than a Milveh Al Peh. The Shulchan Aruch rules like this. (If a man damaged, and sold good and bad land together, the victim collects from the good land - CM 119:3). Even though we hold that a Milveh ha'Kesuvah b'Torah is not like a Milveh b'Shtar in YD 305:16 (regarding Pidyon ha'Ben), we collect damages from Meshubadim. We must answer like the Rashba. This is even if Beis Din did not rule before the damager sold the land; rather, Shibud is mid'Oraisa. Also CM 97:24 shows this (a creditor collects before a wife fed from her husband's property, because her Shibud is only mid'Rabanan) and CM 104:13 (an earlier Milveh Al Peh collects before a later Milveh b'Shtar) like the Rashba explains in Teshuvah 914. (Chachamim removed Shibud of a Milveh Al Peh from buyers, to protect them, but not from the borrower himself.) Indeed, the Rosh holds like Tosfos, like the Shach says, but the Shulchan Aruch rules that Shibud is mid'Oraisa in all these places.