Bari Vishema-The law when a lender claims he is owed money, while the borrower says he thinks he already paid him back:
- The case: Reuvein lent Shimon a certain sum of money, and when he approached Shimon to pay him back his debt, Shimon replied to him that he thinks he already paid him back, but is not certain that that is the case. Does Reuvein still have a right to demand the money, and does Shimon still have a responsibility of paying the full amount being that he doesn’t remember for certain that he paid him back?
The Talmudic and Halachic concept of “Bari Vishema” refers to a scenario in which an individual makes a monetary claim against another for owed funds or for an item, and while he professes certainty in his claim, the individual who he is making the claim against, claims to not remember if he indeed owes him the money, or if indeed the item belongs to him. The person making this claim is referred to as the “Bari/certain” being that he professes certainty in his claim, while the person who the claim is being made against is called a “Shema/maybe” being that on the one hand he is not outright denying the claim, but on the other hand is not acquiescing to it. The arbitration in such a case is complex, and is dependent on various factors such as the strength of the definite claim of the Bari [Bari Tov versus Garua], and the strength of the claim of the lack of knowledge of the Shema [Shema Tov versus Shema Garua]. Likewise, it is dependent on whether the question is on whether the transaction or loan ever took place, or if it definitely took place and the question is simply if it was repaid. The following is the law in our case:
B. The law:
In the event that the lender claims that he is owed a certain amount of money and he is certain that he has yet to be repaid, while the borrower, who does not dispute the loan, claims to have a recollection that perhaps he already repaid him, although does not remember for certain that this is the case, and hence does not make a definite claim of payment, then the law follows the claim of the lender. Thus, so long as the borrower does not dispute the loan, and does not make a counterclaim in which he is certain that he paid him back, then he must repay the lender the full amount that he is claiming that was not paid back. In such a case, the lender is completely believed even without taking an oath. This law applies in all types of loans, whether the loan was written up on a loan document, or whether it was a loan that took place in front of witnesses without being written on a document, or whether it took place just between the lender and borrower without any documentation [i.e. Milveh Al Peh]. In all these cases, the lender must pay back the borrower if he is uncertain if he paid him back while the lender is certain that he didn’t. [If, however, the borrower makes a definite claim that he repaid the loan, than the law is dependent on whether the loan was written on a document, or not.]
Good advice and the Halachic requirement to document payments of loans: Whenever a lender pays back his loan, he should document it and ask for a receipt for the payment, and if there was a loan document involved he should ask for it to be deemed as void, such as to have it torn up, as is indeed required according to Halacha which prohibits a lender from holding onto a loan document that was already paid.
In the event that the borrower does not dispute the loan, but claims to have a recollection that perhaps he already repaid him, although does not remember for certain that this is the case, then the borrower must pay the lender back.
 See Michaber C.M. 75:9; Rambam Toein Vinitan 1:9; Mishneh Bava Kama 118a; Encyclopedia Talmudit 4 p. 199 Erech “Bari Vishema”
 See Tosafus Kesubos 12b; Bava Kama 46a; Baal Haterumos 39:2; Encyclopedia Talmudit ibid
 See Bava Kama ibid for a dispute in this matter, if there is a difference in law regarding if the debt is definite to have occurred or not,
 Michaber C.M. 75:9 and 72:11; Smeh 75:25; Rambam ibid; Bava Kama ibid
 The reason: The reason for this is because a questionable counterclaim cannot override a definite claim of a definite debt. Meaning, that when the debt is definite, then only a definite counterclaim of payment can override it. [Shach C.M. 75:27; Rif Bava Kama ibid; See Taz end of 75 for another explanation] This is unlike the classical case of Bari Vishema in which the question at hand is whether a debt ever existed to begin with, in which case the final ruling concludes that if the debt cannot be proven, then you cannot force the defendant to pay. [Michaber ibid; Rambam ibid 1:8; Rav Nachman and Rav Yochanon in Bava Kama ibid; Kesubos 13a]
 Michaber ibid; Rambam ibid; Rashba 2:160
The reason: As there is no definite claim being made against him for which he must swear. [Shach C.M. 75:28; Rashba ibid]
 See Michaber C.M. 70:1
 If the lender provides a loan document, then even if the borrower claims for certain that he paid him back he is not believed unless he can provide a receipt, as the mere fact that the lender is still holding onto the loan document is a proof that it wasn’t yet paid. [See Michaber C.M. 58, and 57] If, however, the loan was not written up on a document, then the borrower is believed if he claims for certain that he repaid it, although we must take upon himself a Shevuas Heses. [See Michaber C.M. 70:1]
 See Michaber C.M. 57:1
 Rama C.M. 57:1
 Michaber C.M. 57:1