Question

Good evening!
I would like to ask several questions about the parameters of a loan.
1. There is much evidence that repaying a loan is like returning what is his, similar to a borrowed object, even though the borrower borrowed without even a perutah of payment (for example: the Talmud’s statement in Kiddushin that a borrower is liable even for unavoidable accidents, the Rashba’s statement that interest is the rent paid for the money, Rabbi Chaim’s statement that the problem with transferring ownership of a loan is in the legal grasp of the acquisition, not that there is nothing to transfer, and the fact that one repays by measure). True, the conceptual definition is difficult, but my question is from the Talmud in Ketubot 86, that were it not for the commandment of repaying a debt, it would not be possible to compel the borrower to pay (although Nachmanides innovates that this is only according to the view that lien is rabbinic, as discussed below). The difficulty is: how is this different from a borrower of an object, who is taking back what is his?
2. Can one suggest a distinction between returning money, which is like returning the item itself (since ownership of money is over value), and returning movable property and land, which would be considered compensation?

3. Simply speaking, what obligates repayment of a loan is the very taking itself, that is, “my money is in your possession.” But the Rashba in Kiddushin 15 wrote that the movable property of orphans is not subject to lien, because all reliance with respect to movables is only on him himself. My difficulty is that apparently it follows from his words that what creates the obligation to repay is that reliance, a kind of undertaking given in exchange for receiving the money, and not the simple fact that “my money is in your possession.”
And in general, it needs analysis: what obligates repayment of a loan—the taking, “my money is in your possession,” or perhaps the undertaking?

4. What is the reason that according to the Rabbis one does not collect from movable property and money for a ketubah, even not from the husband himself, and how is that different from any other debt? (Though see Tosafot, Ketubot 10, and it still requires analysis.) As for collection from orphans, one could say that their property is not subject to lien, but from him himself, apparently we do not need lien, since what obligates payment is the debt itself?

5. It is explained on page 86 that were it not for the commandment of repaying a debt, they could not compel a borrower to pay. Nachmanides innovated (in Bava Batra 175) that according to the view that lien is rabbinic, there is a solution: through the lien one can compel payment. Apparently his intent is in line with the Ritva, that lien creates a sort of half-acquisition, and therefore the lender has a right of seizure in his property. The question is that, simply speaking, Nachmanides means that if lien is Torah-level, then there is a lien on the borrower’s proprietary domain, and therefore one can seize from it; whereas according to the view that lien is rabbinic, we need the commandment. If so, the difficulty is that according to the Torah-level view, it turns out that two different laws are learned from the same source: both a lien on assets that existed at the time of the loan, allowing collection from purchasers, and also a lien on the borrower’s proprietary domain that allows collection from him himself, whether from land, movables, or money that did not exist at the time of the loan. It is unclear how both are learned from the same source, especially since they are different laws.

6. On that same issue: Rabbi Shimon Shkop expands that even according to the view that lien is rabbinic, there is still a legal debt, for otherwise how could Nachmanides innovate that “instead of compelling him physically, compel him through his money”—what would become of acquisition? It follows, then, that there is still a debt. My difficulty is that if so, there is no difference between the view that it is rabbinic and the view that it is Torah-level, for Nachmanides innovated that according to the Torah-level view we do not need the commandment because there is a lien on the proprietary domain; so how is that different from the rabbinic view, about which Rabbi Shimon Shkop innovated that there is a debt besides the commandment?
[And likewise, it needs analysis whether the commandment resolves only the coercion or also the acquisition.]

Truthfully, I have more questions of this kind, but for now I will present only these.
I would be happy to hear the Rabbi’s opinion—of course, only whatever is easy for the Rabbi to answer without getting deeply into the topic.
Thank you very much!