We are pleased to begin Tractate Bava Metzia, Chapter 1, Mishnah 1 - the famous Mishnah of "two holding a garment": two people holding a single garment and arguing over the right to keep it. The entire chapter will deal with the question of who acquires what and when.
The Fundamental Rule in Monetary Law:
The golden rule regarding acquiring an object is that the possessor - the one who currently holds the object - acquires it, unless "hamotzi mechavero alav haraayah" - the burden of proof rests on the one seeking to extract the object from the possessor, and he must prove that the object actually belongs to the one who is not currently holding it. The standard proof that the extractor must bring is two witnesses who confirm that the object is indeed his.
The Case in the Mishnah:
Our Mishnah discusses a situation where there is no possessor at all: neither of the two is holding a tangible, significant part of the garment, but rather each is just holding the threads at the edge. If each of them were holding an actual piece of fabric, each would keep the piece in his hand, and the Mishnah would only discuss how to divide the fabric between the two pieces - the part that no one is holding.
"Shenayim ochazin betalis, zeh omer ani metzatiha vezeh omer ani metzatiha" - two people are holding a single garment, each by opposite edges, and each claims: I am the one who found it, meaning I am the one who lifted it first. Merely seeing an object does not acquire it, but lifting it does, and therefore each of them claims that the entire garment belongs to him.
Obviously, this discusses a case where there is no obligation to return a lost item. Usually, one who finds a lost item is obligated to return it to its owner, but here there is no obligation to return it for some reason: it has no identifying mark, or the case takes place in a city where the majority are non-Jews, and so on. The question is, therefore, how we rule.
The Second Part of the Mishnah - A Separate Case:
"Zeh omer kulah sheli vezeh omer kulah sheli" - seemingly, this appears to be a direct continuation of the first case, but the correct understanding is that this is not a single case of "I found it and it is all mine", but rather a completely different case: here they are not claiming that they found the item, but rather each claims that he legally purchased it. This is a sort of marketplace situation: the garment is offered for sale, it is the last one left, they are both fighting over it, and they both push money into the hands of the merchant. The merchant intended to sell to one of them, but does not remember to whom - there were two hands and money reached out to him. Now they are both holding it, each believes that it is his and claims that he is the one who bought it with the merchant's consent, and therefore each says that it is all his.
It is worth noting that in both cases it is possible that neither of them is lying: while it is possible that one of them did indeed lift it first, it is also possible that they both lifted it together at the exact same moment, and each truly and innocently believes that it is all his - and they are both mistaken. The same applies regarding purchasing the item.
The Ruling of the Mishnah and the Nature of the Oath:
The Mishnah establishes that in both cases - regarding the found garment and the purchased garment - each of the two will swear that he owns no less than half of it, and then they will divide the garment equally. This obligation to swear is a Rabbinic law: according to strict Torah law we would divide it between them regardless, but the Sages said that without deterrence, swindlers would come and grab onto garments that others are holding, bring them to court, and acquire half of what is not theirs. To deter an act that is actual theft, we obligate them to swear before allowing them to take half.
If you ask, as the Gemara asks: If we already suspect that the person stole, what good is his oath? The answer is that people fear an oath more than they fear taking their fellow's money. Even someone who is suspected regarding money, and makes light of the money of others, does not make light of a false oath so easily.
A Case Where One of Them is Certainly Lying:
What is the law when each of them claims that he wove this tallis, in which case it is clear that one of them is lying?
The View of Tosafos: It is obvious that the same law applies. They are both in disagreement, beis din does not know who is right, both claim that the entire tallis is theirs because they made it, and neither of them has an established claim to anything - and therefore they divide it with an oath, which is a rabbinic oath.
The View of Rashi: We cannot accommodate a situation where one is a complete fraudster and give the fraudster half of the tallis. In his opinion, the tallis is placed in beis din in a status of "yehei munach" - let it rest - until Eliyahu HaNavi comes and rules to whom it belongs. Until then, it is not given to either of them, since beis din is not prepared to actively rob half of the tallis from its owner.
This makes sense: although it is not fair to the true owner, who now loses the entire tallis due to his fellow's false claim, it is clear that if the law dictates that one who makes such a false claim receives nothing - he will not do it again.
When the Merchant Testifies in Favor of One of the Parties:
In the case of a purchase, what is the law if the merchant says that he sold the tallis to Reuven? Since both parties base their claim on the merchant, the merchant himself is only a single witness, whereas to extract money a complete proof of two witnesses is required; a single witness is only half a proof. However, the rule is that a single witness who supports a claim obligates the opposing party to take a Torah-level oath - one of the cases where a person is obligated to take an oath from the Torah is when there is a single witness against him. It emerges that Reuven and Shimon are arguing over the tallis, the merchant testifies that it belongs to Reuven, and Shimon is now obligated to take a complete Torah-level oath with all its severity.
And what about Reuven himself - must he take the rabbinic oath that our Mishnah obligates? From the words of Tosafos and the Rosh it appears not: once he has the support of a single witness, he is exempt from the logic that obligates him in this oath. However, from the wording of the Rambam it implies that he is nevertheless obligated.
"Zeh omer kullah sheli v'zeh omer chetzya sheli" - This one says it is all mine and this one says half of it is mine:
The Mishnah continues and discusses a case in which one claims, "kullah sheli" - it is all mine - I found it and lifted it first - while his fellow claims, "chetzya sheli" - half of it is mine: we found it and lifted it together, and therefore it belongs to both of us and must be divided. Here, the same fundamental rule applies as in the first part: regarding the disputed portion, they take an oath that they do not own less than half of it, and they divide it equally.
And therefore the Mishnah states: "Ha'omer kullah sheli - yishava she'ein lo bah pachot mi'shloshah chalakim, v'ha'omer chetzya sheli - yishava she'ein lo bah pachot me'ravia, zeh notel shloshah chalakim v'zeh notel ravia" - One who says it is all mine takes an oath that he does not own less than three parts of it, and one who says half of it is mine takes an oath that he does not own less than a quarter of it, this one takes three parts and this one takes a quarter. The one who claims that it is entirely his takes an oath that he has no less than three quarters of it, and the one who claims that half of it is his takes an oath that he has no less than a quarter of it, and ultimately the first takes three quarters and the second takes a quarter.
And the reason for the division: Since the second claims, "chetzya sheli" - half of it is mine - he admits that half of the tallis belongs to the first. There is no dispute at all regarding this half, and the first takes it. The second half remains, regarding which each of them claims that it is entirely his - and they divide it equally with an oath. It emerges that the first takes three quarters and the second takes a quarter.
The wording of the oath:
The Gemara explains that in the case where both claim "It is entirely mine," the text of the oath includes two parts: "Shevuah sheyesh li bah" - I swear that I have a share in this garment, "ve'ein li bah pachot mechetzyah" - and that my share in it is not less than half. Even though the Mishnah only mentioned the second part, the Sages were concerned that a person might try to play a word game: when swearing "I do not have less than half of it," he will intend in his heart that indeed he does not have a share in it that is less than half, because he has no share in it at all. Because of this trickery, they instituted a two-stage oath: that I have a share in it, and that my share in it is not less than half.
The same applies in the second part of the Mishnah: the first one says that he has a share in it and that it is not less than three quarters, and his friend says that he has a share in it and that it is not less than a quarter, and the division is made accordingly.
And if you ask: Why does the first one need to swear on three quarters, when his friend already conceded half to him? Let him swear only on the disputed quarter, and similarly his friend, and by virtue of this they would divide it into three quarters and a quarter. The answer is that we must be concerned about a similar word game: the one swearing on a quarter will intend in his mind that very quarter which belongs to him anyway, and not the quarter in which he truly only has a half, since in reality they found it together. Therefore, they obligate him to swear on the entire three quarters, so that he stands behind his oath.
And if you ask regarding both cases: Why do we not make them swear on their full claim? In the simple case, where Reuven claims it is entirely his and Shimon claims it is entirely his - let each swear according to his claim, that it is entirely his. The answer is that then the Beis Din would appear as though it is not acting properly: people swear that it is entirely theirs, and they are not given what they swore about. Therefore, we make them swear that they do not have less than half in it, and then we give each one a complete half, so that what is actually given matches the wording of the oath.
In summary: In this Mishnah, we learned the law of "two are holding a garment" in two cases - a garment that was found and a garment that was bought - in both of which each swears that he does not have less than half of it and they divide it equally, with the oath being a rabbinic enactment intended to deter fraudsters. We discussed the dispute between Tosafos and Rashi in a case where one of them is certainly lying, the law of a single witness that obligates a Torah oath, the division in a case of "it is entirely mine" versus "half of it is mine", as well as the exact wording of the oath and its reasons.