In the previous Mishnah we learned about one who takes an oath and collects, and about one who pays half of the claim. Now we move on to Mishnah 5, which presents another case in which the Sages permitted a claimant to take an oath and, on the strength of that oath, to extract money from the defendant: the case of the shopkeeper and his ledger - the storekeeper holding the account book in which he records his transactions.
The practice of selling on credit:
The practice in the time of the Gemara, which is still with us today even though we have far more sophisticated and technological methods, is selling on credit. The shopkeeper, the owner of the grocery store, sells to customers who have no cash on hand and are waiting for their paycheck to arrive, and he records the debt in his ledger: so-and-so bought a pound of flour and a pound of sugar and owes five dollars; someone else bought a dozen eggs and a bottle of milk and owes four dollars. And so he has before him an orderly record of the debts.
How, then, does the shopkeeper become trusted to come to beis din with his ledger and say: my ledger testifies that this one owes me five dollars and that one owes me four dollars, and to collect from them even when they deny it and claim that they paid?
The Mishnah qualifies:
"Lo she'yomar lo: kasuv al pinkasi she'atah chayav li masayim zuz" - a person cannot come and claim: my ledger testifies that you owe me two hundred zuz, pay me. In such a situation he is not believed, and the shopkeeper does not take an oath on the basis of his ledger alone, since anyone could forge a ledger.
The case the Mishnah is dealing with:
The householder - that is, the customer, whom the Mishnah and the Gemara call by this term in contrast to the shopkeeper - approaches the shopkeeper and says one of the following two things:
"Ten li'vni sa'sayim chitin" - he sends his son on an errand to the store to receive two se'ah of wheat.
"Ten l'po'alai b'sela ma'os" - he hands the shopkeeper a sela, a coin worth a fixed number of ma'os, and asks him to give his worker its value in small coins. In today's terms: he hands over a hundred dollar bill and asks him to give the worker the change - ten bills of ten.
Some time later the shopkeeper comes and demands his money: "I gave your son two se'ah of wheat, give me their value; I gave your worker ten ten dollar bills, give me the hundred dollar bill." The householder responds: "I paid you through my son - my son took the two se'ah and paid you."
The son and the worker, for their part, deny it: "We took nothing, we never came to the store at all, and the householder owes you nothing." Against them the shopkeeper takes an oath: it is written in my ledger that your son came and took two se'ah of wheat; it is written in my ledger that your worker came and took ten ten dollar bills. The son and the worker also take an oath, and they collect their claim - their wages from the householder - on the claim that they do not believe the shopkeeper.
Taking the oath in one another's presence:
The Gemara explains that in this case both parties swear, the son or the worker on one side and the shopkeeper on the other, in each other's presence. For it is impossible that both of them are telling the truth: if the shopkeeper says "I gave it to your son and you owe me money," and the son says "I never took anything from him," then necessarily one of them is swearing falsely. Therefore we require that both of them swear in one another's presence, in the hope that one of them will feel ashamed and admit the truth.
The View of Ben Nanas:
Ben Nanas did not accept this arrangement: two litigants come to beis din, and we permit both of them to swear while we know that one of the oaths is a false oath - how can such a thing be allowed? There are several ways to read his words, and according to one of them: "zeh o zeh" - this one or that one is certainly swearing falsely, and that is a terrible chillul Hashem. We must not create a situation in which we effectively obligate a false oath, since one of them is bound to lie.
Ben Nanas therefore holds that the oaths should be cancelled entirely: the shopkeeper takes his money, the son or the worker takes his wages, and the poor householder is the one who loses out, as it were.
In summary: in this Mishnah we learned the law of the shopkeeper and his ledger: the ledger by itself is not proof, and the shopkeeper is not believed to say "it is written in my ledger that you owe me." But when the householder sent his son or his worker to the shopkeeper, and the parties come and contradict one another, the shopkeeper and the son or the worker swear in each other's presence and collect, in the hope that one of them will feel ashamed and admit the truth. Ben Nanas disagreed and held that we must not create a situation that necessarily leads to a false oath, and therefore both of them collect and the householder is the one who loses out.
With this we have completed the fifth Mishnah in our study of Maseches Shevuos.