Bava Metzia, Chapter 5, Mishnah 9. The Mishnah continues to discuss loans made "seah be'seah" (a seah for a seah) - lending a fixed amount with the condition of returning that exact same amount - which is rabbinically prohibited. The leniencies that apply to commercial buying and selling also apply to seah be'seah: if "yesh lo" (he has it - the merchandise is in his possession), or if "yatza hashaar" (the market price has been established - there is a fixed and public price in the market) - it is permitted to borrow seah be'seah. Our Mishnah deals with the first of these, the leniency of "yesh lo," and teaches a novel concept regarding it.
The Prohibition of Lending Seah Be'seah:
"Lo yomar adam lachaveiro: halveini kor chitin va'ani etten lecha lagoren" - A man may not say to his fellow: "Lend me a kor of wheat and I will give it to you at the threshing floor." A kor is thirty seah. A person is not allowed to simply borrow seah be'seah, telling his friend: Give me thirty measures of wheat, and I will return thirty measures of wheat to you after the harvest, when it comes into my hands. The permitted way is to establish the monetary value in advance: the thirty measures of wheat are currently worth a thousand shekels, and I will return wheat worth a thousand shekels to you when the time comes.
The Leniency of "Yesh Lo":
"Aval omer lo" - But he may say to him. If "yesh lo," meaning he already has wheat in his possession, he is allowed to borrow more. Not only that, but even in these two cases:
"Halveini ad sheyavo beni" - "Lend to me until my son comes." He has wheat, but it is not physically with him: it is with his son, who has not yet arrived and is on his way.
"Ad she'emtza mafte'ach" - "Until I find the key." The wheat is sitting in his storehouse, but the storehouse is locked and he cannot enter it; and until he finds the key, he needs wheat right now, during the planting season.
In both of these cases, it is considered "yesh lo." And this is the novel concept: even though the wheat is not physically in his hands, and he cannot even access it now if he wanted to. After all, the rationale for "yesh lo" is that the lender could theoretically acquire it now if he wanted to, and if he does not do so, it is as if the loan is completely backed - meaning, it was in his power to transfer ownership to him. Here, he cannot transfer ownership even if he wanted to, since he has no access to his wheat and there is no way to perform an act of acquisition on behalf of the lender, yet nevertheless it is considered "yesh lo," and that is sufficient.
The Difference Between Buying and Selling and Seah Be'seah Regarding This Leniency:
Furthermore: although this is not reflected in the Mishnah, the halachah is that even if a person only has a portion of the amount he is borrowing, he is allowed to borrow seah be'seah. This is an important difference between buying and selling and seah be'seah regarding the leniency of "yesh lo":
In buying and selling: If I committed to supply wheat in the future and I have ten bushels in my warehouse, I am allowed to take money now for the supply of at most ten bushels, since this is all I have under the category of "yesh lo." If I agree to supply fifteen bushels, it turns out that five of them are not "yesh lo," and this is prohibited.
In seah be'seah: Even if I only have ten in my warehouse, I am allowed to borrow fifteen, since it is enough that I have a fraction of the amount for it to be considered "yesh li." And this is a very great leniency.
The Opinion of Hillel:
"Vehillel oser" - And Hillel prohibits. Hillel the Elder, from the pair of Shammai and Hillel, is stringent and prohibits, and the halachah does not follow him. In his opinion, if a person does not have direct access to his grain right now - because it is in the hands of his son who has not yet arrived, or it is locked in the storehouse - he is prohibited from borrowing seah be'seah, and he must evaluate its monetary value right now, since it is not considered "yesh li" when he does not have access to it.
Hillel had an additional stringency, and here too, the halachah does not follow his view: "Lo salveh isha kikar lachaverta ad sheta'asenu damim" - a woman may not lend a loaf of bread to her friend until they evaluate its accepted market price, "shema yokiru chitim venimtza'u ba'os lidei ribis" - lest wheat become more expensive and they end up coming to ribis. Hillel's concern is that this is a case of lending a se'ah for a se'ah: the price of wheat might go up, so that at the time she borrowed it, the loaf was worth ten shekels based on the price of wheat, and when she returns it, the wheat has already gone up and the price of bread in the store has risen to eleven shekels - meaning she ends up giving a shekel of ribis. Even though this is only a rabbinic prohibition, it is still a prohibition.
Practical Halachah:
The halachah does not follow Hillel's view. When dealing with very small amounts, such as the possible price fluctuations of a loaf of bread, neighbors are not particular with one another and a person does not pay attention to a change of a few pennies. Therefore, they completely forgive this, and the Sages thus did not decree against it, so it is permitted. This is not the case with an actual monetary loan, where one cannot leave any extra change and cannot pay even a single extra penny; however, here, where the entire issue is only the rabbinic prohibition of lending a se'ah for a se'ah, when the amount is minuscule and people are not particular about it - it is permitted, and this is the halachah.
Nevertheless, it is highly recommended to agree with one's neighbors once and for all (with Jewish neighbors, at any rate) that any borrowing or lending between you is done as a gift from one to the other, and the return is made as another gift. This is very important, as it happens countless times: a person comes to borrow and needs milk, and the neighbor only has half a carton - and a "half carton" means any amount between twenty and eighty percent of a milk container. At the time of the return, the borrower does not know how much to give or what to give: should they add a bit, should they return less, and is there an issue of ribis here. By establishing in advance that everything transferred between you - the milk, the sugar, the oil and the like - is given as a gift from one to the other, the problem is completely solved. This is true even though, as mentioned, according to the strict letter of the law, if one returns an approximate amount that people are not particular about, it is permitted.