1) THE DIFFERENCE BETWEEN "DINA" AND "KENASA"
OPINIONS: The Mishnah (93b) states that when a person buys grain, he accepts that there will be up to a quarter of a Kav of Tinofes (the Gemara discusses whether this refers to dirt or legumes) per each Se'ah of grain that he buys. (This equals 1/24 of the total amount, as there are six Kav in a Se'ah.) The Gemara cites Rav Huna who says that if a buyer notices that the grain appears to have more than the acceptable amount of Tinofes, he is entitled to demand that seller sift the entire amount of grain and give him only pure grain.
The Gemara explains that the source of this law is either "Dina" ("law") or "Kenasa" ("penalty"). "Dina" means that the source of this law is based on logical considerations: a buyer accepts the fact that the grain he buys might contain up to a quarter of Tinofes, and he does not care if his Se'ah of grain contains slightly less than a true Se'ah of grain. However, he does care if his grain contains more than a quarter of a Kav of Tinofes per Se'ah. Once he decides to buy such grain and demands that it be sifted, he cares to ensure that the grain he is buying should not have any Tinofes. The seller therefore has no right to sell any Tinofes with the newly sifted grain.
"Kenasa" means that this law is a penalty that the Chachamim instituted. It is normal that a Se'ah of grain contains up to a quarter of a Kav of Tinofes. If a Se'ah of grain has more than that amount of Tinofes, it is a sign that the seller purposely attempted to included more Tinofes in the sale. The Chachamim therefore penalized the seller and required that he resift the grain and sell pure grain with no Tinofes.
Is there any Halachic difference between these two opinions about the source of this law?
(a) The RASHBAM (DH v'Amri Lah Kenasa) writes that the difference between these two opinions exists in a case in which it is known for a fact that the seller did not purposely mix more than one quarter of Tinofes in the grain (for example, the customer saw that the seller opened a new bag of grain from a standard grain supplier and spilled it into his tray for sale). If this law is based on logical considerations, then the customer still does not want to purchase grain with so much Tinofes and the seller must resift all of the grain in question. However, according to the opinion that this law is a fine (due to the suspicion that the seller tampered with the amount of Tinofes in the grain), the fine should not apply in this case because the seller clearly did not tamper with the grain. Accordingly, the seller should be able to give the buyer more than a Rova of Tinofes.
The RAN has difficulty with the Rashbam's explanation. Why should the seller ever be entitled to sell more than one quarter of a Kav of Tinofes? This is a standard amount which the Mishnah prohibits a seller from selling with a Se'ah of grain!
(b) The RAN explains says that the Rashbam's until this point is correct. However, he explains that if the reason is "Dina," the grain must be totally resifted even when it is known that the seller did not tamper with the grain. If the reason is "Kenasa," the seller still must resift the grain, but he is required to remove only the amount of Tinofes above the permissible amount. He may leave one quarter of a Kav of Tinofes in the grain.
The Ran quotes RABEINU YEHUDAH BAR CHISDAI who explains that because the source of this law is unresolved, the Halachah is that the person who is in possession of the money keeps the money. Accordingly, in a case in which it is known that the seller did not tamper with the grain, the seller does not have to resift the grain and he may leave up to one quarter of a Kav of Tinofes in the grain.
(c) RABEINU CHANANEL apparently understands that there is no significant Halachic difference between these two opinions. The only difference is whether one may extrapolate the law from this case to other cases. If the law in this case is "Dina," then it may be applied to other cases. If it is "Kenasa," then it cannot be applied to other cases (since each situation of a fine is unique).
The Ran points out that this also seems to be the approach of the RAMBAM (Hilchos Mechirah 18:11). The Rambam states merely that if a seller gives the buyer too much Tinofes with the grain, he must resift the entire amount. This implies that even if it is known that the seller did not intentionally tamper with the grain, he still must resift the entire amount of grain and remove all of the Tinofes. The Ran suggests that the Rambam understands that the principle of "Lo Plug" applies in this case, and thus a seller must always resift the grain when the grain that he has sold appears to contain more than a quarter of a Kav of Tinofes. (Y. MONTROSE)
2) REBBI MEIR'S OPINION IN THE CASE OF A CONTRACT WHICH CONTAINS A CLAUSE OF INTEREST
OPINION: The Gemara says that in the case of a loan document which shows that a person lent money with interest, Rebbi Meir rules that the lender is penalized in that he may collect neither the principal nor the interest of the loan.
Does this mean that the document is rendered null and void and the lender is never allowed to collect his loan at all, or does it mean that although the document is rendered useless, if witnesses come to Beis Din and testify about the loan, the lender may collect the principal?
(a) TOSFOS (DH Konsin) quotes the RI who says that the lender is not allowed to collect the loan at all, even if the borrower admits that he borrowed money, or if witnesses come to Beis Din and testify about the loan. The wording, "he does not collect," implies that he may not collect at all.
The RIVAM asks that while this penalty is a fitting punishment for the lender for lending with interest, in what way is the borrower penalized for borrowing with interest? The Torah prohibits a person not only from lending with interest, but also from borrowing with interest. Why should the borrower gain (by not having to pay back anything) as a result of his sin of borrowing with Ribis? The Ri answers that since the lender is the one who profits from a loan with interest, it is he who is penalized. The borrower merely needs a loan and stands to profit nothing from this specific transaction, and thus he is not penalized (and the Chachamim do not mind that he is indirectly rewarded).
(b) TOSFOS in Bava Metzia (72a, DH Shtar) quotes the RIVAM who explains that when Rebbi Meir says that the lender may not collect the principal and the interest, he means that he may not collect Meshubadin (land of the borrower which is automatically collateralized when a Shtar is written) on the basis of the Shtar. He may collect, however, the principal of the loan from other assets (Nechasim Bnei Chorin). The TOSFOS RID here explains that the Rivam's logic is precisely as recorded by Tosfos here: since the borrower also sinned by borrowing with interest, why should the borrower profit from his sin? (The Tosfos Rid sides with the opinion of the Ri quoted by Tosfos.)
Tosfos in Bava Metzia questions the position of the Rivam. The Mishnah in Bava Metzia (75b) derives from the verse, "Lo Sesimun Alav Neshech" -- "you shall not lay upon him interest" (Shemos 22:24), that the Torah prohibits witnesses from testifying on a loan document which includes a clause of Ribis. Witnesses who testify on such a document transgress a Torah prohibition and are classified as evildoers, and thus are disqualified from serving as witnesses. Accordingly, there are no valid witnesses signed on the Shtar. Why, then, according to the Rivam, may the lender use this Shtar to collect from Nechasim Bnei Chorin? The Shtar is invalid without the signatures of valid witnesses!
Tosfos (72a) answers that it is possible that the Gemara is discussing a case of Ribis d'Rabanan. Since the prohibition is only mid'Rabanan, the witnesses who sign the Shtar do not become Pasul l'Edus. (As Tosfos explains, although a witnesses becomes Pasul l'Edus when he transgresses an Isur d'Rabanan, this applies only when he transgresses an Isur d'Rabanan for a profit. In this case, the witnesses gain nothing by signing the Shtar.)
In his second answer, Tosfos suggests that the Gemara indeed refers to a case of Ribis d'Oraisa. Nevertheless, a person becomes Pasul l'Edus only when he transgresses a Torah prohibition which people know applies to him. In the case of witnesses who sign a loan document which includes a clause of Ribis, it is possible that most people think that when the Torah says "Lo Sesimun," it refers to the lender, not to the witnesses. (See a similar example in Bava Metzia 5b.) Therefore, the witnesses who sign the Shtar are not deemed Pasul l'Edus. (Y. MONTROSE)