פירוש על בבא מציעא 41:14

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].

Because they are not of significant [value] - to him, the kav of produce, to exert himself for them with the exertion of gathering [them] over four [by four] cubits.

A half-kav in an area of two cubits, what is [the law] - It is a wonder: Is a kav in four cubits not also a half-kav in two cubits (is the ratio not the same); so what is he inquiring? And one can say that since there is only a half-kav, he will take [them] since there is no exertion [beyond this] to finish. But [with] a kav in four cubits, since there is exertion to take all of it, he does not take [them] at all. Or also (another answer), a kav in four by four cubits is [the same as] half a kav in two cubits width by four cubits length, whereas here he is inquiring about two cubits by two cubits.

A half-kav in an area of two cubits, what is [the law] - It appears that it means two cubits by a length of four cubits, which is half of four by four cubits. For if it was two cubits by two cubits, it would only be a quarter. And likewise also, "two kav in an area of eight cubits" does not mean eight by eight, but rather eight by four.