What happens if two brothers agree on dividing up their inheritance, only to discover that there is a third brother who appears and demands to receive his share?
Our Gemara presents just such a case – two brothers divide the inheritance and a third brother comes from a far-away land – and brings a disagreement between Rav and Shmuel. Rav rules that in such a case the agreement falls apart and a new arrangement must be made. Shmuel rules mekametzin – each of the brothers takes part of what he received and gives it to the newly arrived brother so that he gets an equal share.
Rav’s reasoning is fairly straightforward. Although the original agreement had the force of a kinyan – of a legally binding claim of ownership – nevertheless we have discovered that it was done mistakenly, and therefore it needs to be done over again.
Shmuel’s ruling is subject to a number of different explanations. The Rashbam says simply that the original division remains in effect, but each of the two brothers who received a share will be obligated to take half of the amount that the third brother deserves and give it to him. According to this approach, the term mekametzin means to take a part of something, like the passage in 2:2.
Tosafot reject this reading of Shmuel, arguing that the two brothers do not have the right to determine what the third brother should receive. They explain that even according to Shmuel the third brother enters into negotiations about the part that he will receive, however the first division still remains in effect inasmuch as whatever he does not take will revert to the individuals who agreed to get it in the first place. According to this explanation, the term mekametzin appears to be related to the word kamtzanut – frugality or lessening the need for further divisions.
The Ri Migash argues that even according to Shmuel the third brother can demand a new division of the estate. It is only if he agrees to accept what the brothers set aside for him that there is no need to redivide the estate from the beginning.