פירוש על בבא מציעא 42:10

Which found items are [the finder's], and which is he obligated to proclaim? These found items are his: If he found scattered produce, scattered coins, bundles [of grain] in a public area, round cakes of figs, bread of a baker, strings of fish, cuts of meat, unprocessed wool fleeces that are taken from their state, flax stalks or strips of combed purple wool, these belong to him. In the Gemara, we establish [the case of] scattered produce to be a kav in four cubits in the gathering [of grain] on a threshing floor. For that is a loss of which one is aware; as the owners do not want to exert themselves for a kav that is scattered over four cubits, so he abandons them. Scattered coins do not have an identifying mark, and are knowingly abandoned, like that [statement of Rabbi Yitzchak - since a person is accustomed to feeling in his purse all the time, he will know that they fell before they come to the hand of the finder. Bundles in a public area, according to Rabbah, are when they have an identifying mark, but it is prone to be trampled; so the owners do not rely on that identifying mark and abandon [them]. But in a private area, such as a plowed field, they are not prone to be trampled, so he is obligated to announce [his finding it]. And in these [other cases], it makes no distinction between a public area and a private area. With piles of fruit, [however,] we do not trample them; and piles of coins do not move from their place by being trampled. And according to Rava, [the case of bundles] is speaking about when they do not have an identifying mark - so in a private area, [the owner] can give the place as an identifying mark; but in a public area, it rolls around from the feet of people and the feet of animals, so they did not have the place as an identifying mark. But in all of these [other cases], it does not distinguish [between a private area and a public area], since it is not the custom to place them on the ground, but they rather fell in the way of being dropped - and they do not have an identifying mark, so [the owners] abandoned them. But the standard case of bundles is [that it is found] in the manner of being placed - when a man stops to rest and puts down his load and they stayed there through some incident. So the owners abandon [them], since they do not have an identifying mark; and not everyone knows that one may not take [an object when there is] a doubt that it was placed down, and all the more so [when it is] certain - so they will take them........ Rabbi Yirmayah inquired, what about a half kav in two cubits by two cubits, since their value is less but their effort is [also] less; two kav in eight cubits by eight cubits, since their value is more but their effort is [also] more; a kav of sesame seeds in four cubits, since they are significant (in value), but their effort is greater; a kav of dates or a kav of pomegranates in four cubits, since they are not significant (in value), but their effort is less? It was not resolved. And since it was not resolved, we are strict concerning a doubt in a Torah law, so one is obligated to announce [his finding it].

Come and hear, one who finds coins, etc. - It is a wonder: Since it already brought a difficulty from our mishnah about scattered coins, why does it also challenge from this baraita? And also why did Rabbi Yitzhak not say his piece about our mishnah? And it can be said that it was stronger for it to raise a difficulty on the baraita, since it implies that it is the [finder's] in all cases - even in the case where there is an identifying mark, since it establishes the reason to be because the multitudes are found there. And it is also implied [that this is the case] even though the owner of the lost object was still in the study hall when [the finder] picked it up, and he didn't know that it had fallen from him.