Prozbul Legal Fiction or Moral Fact?

A widow can collect [her ketubah] from the orphans' property only if she takes an oath [that she did not receive from her husband while he was still alive]. The courts [began] refraining from facilitating the oath, so Rabban Gamliel enacted that the orphans be allowed to have the widow [make an additional] vow [as insurance], so she can collect her ketubah.

Witnesses sign a get (divorce document), for the sake of society's sustainability (tikkun olam).

Hillel enacted the prozbul for the sake of society's sustainability.

(3) [A loan secured by] a prozbul is not cancelled. This was one of the things enacted by Hillel the elder; for when he observed people refraining from lending to one another, and thus transgressing what is written in the Torah, “Beware, lest you harbour the base thought, [‘The seventh year, the year of remission, is approaching,’ so that you are mean to your needy kinsman and give him nothing.” Hillel enacted the prozbul.

Bulei and Butei - The rich and the poor; the rich, so they will not lose, and the poor, so they will not have doors slammed in their faces.

(3) "and what you have with your brother your hand shall release": and not one who hands over his bills (of indebtedness) to beth-din (i.e., Beth-din may present the bills for him; for then it is not his hand, but their hand that is doing so.) It is for this reason, for the general welfare, that Beth-Hillel instituted the prozbul (a declaration before the beth-din authorizing them to claim one's bills). For he saw the people ceasing to lend one another and transgressing (Ibid. 9) "Take heed unto yourself lest there be in your heart a thing of wickedness, etc." He, therefore, arose and instituted the prozbul. And this is the text of the prozbul: "I transfer to you, so and so, the judges, in this and this place, every debt owing me, that I may collect it whenever I wish." And the judges or the witnesses sign below.

They questioned if [Hillel's enactment of the] prozbul truly was a Torah law. They answered that when Hillel enacted it, he relied on Torah law, specifically on that verse (Deut. 15:3, see below), that just as the Torah excluded the remittance of debt if the chit had been transmitted to the court, so, too, once the prozbul was established, with the chit prima facie handed over to the court, that the debt would not be remitted.

As it is taught in a baraita that Rabbi Yehuda HaNasi says: The verse states in the context of the cancellation of debts: “And this is the manner of the abrogation: He shall abrogate” (Deuteronomy 15:2). The verse speaks of two types of abrogation: One is the release of land and one is the abrogation of monetary debts. Since the two are equated, one can learn the following: At a time when you release land, when the Jubilee Year is practiced, you abrogate monetary debts; at a time when you do not release land, such as the present time, when the Jubilee Year is no longer practiced, you also do not abrogate monetary debts. And the Sages instituted that despite this, the Sabbatical Year still will abrogate debt in the present, in remembrance of the Torah-mandated Sabbatical Year. Hillel saw that the people of the nation refrained from lending to each other so he arose and instituted the prosbol. According to this explanation, the ordinance of Hillel did not conflict with a Torah law; rather, he added an ordinance to counter the effect of a rabbinic law. According to this explanation, the Sages instituted that even in the present the Sabbatical Year would bring a cancellation of debt, despite the fact that by Torah law the debt still stands. The Gemara asks: But is there anything like this, where by Torah law the Sabbatical Year does not cancel the debt, and the Sages instituted that it will cancel? It is as though the Sages are instructing the debtors to steal from their creditors, as by Torah law they still owe the money. Abaye says: This is not actual theft; it is an instruction to sit passively and not do anything. The Sages have the authority to instruct one to passively violate a Torah law, so long as no action is taken. Rava says: The Sages are able to institute this ordinance because property declared ownerless by the court is ownerless.

Since handing over documents to the court was already an available option, why did Hillel have to establish the Prozbul? One can say it is because not everyone wanted to hand over their documents, or sometimes one was not able to [i.e. the Prozbul took care of that from the outset].

If the borrower has land, but the lender does not, one can write a Prozbul. If the lender has land, but the borrower does not, one cannot write a Prozbul. If [the borrower] owns no land, but their guarantors do, or those who owe [the borrower money] do, then one can write a Prozbul.

(6) A prozbul is written only for [a debt secured by] land. But if [the debtor] has none, then [the creditor] can give him title to a share, however small, of his own field. If he had land in pledge in a city, a prozbul can be written on it. Rabbi Hutzpit says: a prozbul may be written for a man on the security of his wife's property, or for an orphan on the security of property belonging to his guardian.

...One can say that the Prozbul was not a protective fence, lest the Torah be abrogated, but rather the opposite: the Torah clearly said to remit [the debts], but Hillel disrupted and established that the debts remain in force. And even though it says that Hillel enacted the Prozbul because he saw that people were refraining from lending money to each other and thus violating what the Torah said, "Take care not to murmur in your heart to withhold," since it was not really a negative commandment they violated in refraining from lending money, but rather neglect of performing a positive commandment (which is bad, but not as bad).

Rather, the real reason for the Prozbul was not to protect the Torah but rather an enacted policy to protect the poor, so the door is not shut in their faces [when they are in need], and even for those with funds, so they do not lose out... And now it makes sense why Rav Chisda said that it is called a Prozbul because it's a rule for the rich not to violate the Torah's principle, but from our explanation, it is also an enactment for the poor, not as a protection of the Torah, but as a reparation.

§ And Rav Yehuda says that Shmuel says with regard to abrogation of debts: In the case of one who says to another the stipulation: I am lending you money on the condition that the Sabbatical Year will not abrogate my debt, even if the borrower agrees to that stipulation, the Sabbatical Year abrogates the debt. The Gemara suggests: Let us say that Shmuel holds that the lender who proposed that stipulation is one who stipulates counter to that which is written in the Torah, and in the case of anyone who stipulates counter to that which is written in the Torah, his stipulation is voided.