In the first case of the Mishna on 2a, both persons claim "it is all mine." However, they are only obligated to swear that they own half of the garment. Why don't they both swear that they believe it all belongs to them if that's what they originally claimed? (This type of question could also be asked for the other cases in the Mishna) Perhaps one of them really only believes that half of the garment belongs to him--then he would only have the right to 1/3 of the garment?
Jason Behar, Jerusalem, Israel
(1) Your question is anticipated by Rashi in the Mishnah DH she'Ein who cites the Gemara below 5b which explains why this wording of the oath was instituted. In fact the Gemara there cites Rav Huna who said that each one swears that he owns some of the Tallis and that he does not possess less than one half of it. The Gemara then asks your question: Why does each contestant not swear that all of the Tallis belongs to him if that is what he believes? To this the Gemara answers with a rhetorical question: Would we give him all of the Tallis on the basis of this oath?
(2) Rashi DH Mi explains the latter answer to mean that we could not in fact give him all of the Tallis even if he was to swear that he owns it all, because since his contestor is grasping on to the other half, we cannot take it away from him with a mere oath. If he should swear that he owns the entire Tallis, this would be comparable to spreading bad rumours about the Beis Din since he claims that it all belongs to him and they only give him half.
(3) The Shitah Mekubetzes 5b explains that Rashi means that if he would make an oath that he owns all of the Tallis and the Beis Din should only give him half of it, this will lower the esteem of the Beis Din in the eyes of the public because the contestor swore that the entire Tallis belonged to him, so since Beis Din only give him a half, this means effectively that he is making an oath that the Beis Din is not deciding the case correctly.
(4) If one of them only believes that he owns a half, and the other claims he owns it all, the continuation of the Mishnah states that in this case the one who claims a half actually only receives one quarter.
KOL TUV and Chag Sameach
D. Bloom