Gemara

29b (Mishnah): If he finds a bag, box or anything that normally he would not carry it, he leaves it there.

30a (Beraisa): We learn from "v'His'alamta" - sometimes you ignore an Aveidah, and sometimes not. If a Chacham sees an Aveidah that it is undignified for him to carry it, he ignores it.

30b - Question: If the Chacham would return it in the field (where few see him), but not in the city, must he take it from the field to return it to the city?

Since he is not obligated to fully return it, he need not start;

Or, in the field, he is obligated to take it, and once he starts, he must finish!

This question is not resolved.

(Rabah): If the Chacham hit the animal (so it will return to its owner), he is obligated to return it.

Rishonim

Rif: The Gemara did not resolve the question of an Aveidah that a Chacham would return it in the field, but not in the city. Therefore, he does not return it in the city.

Hagahos Chavos Ya'ir (2): The text of the Rif should say like the Rosh cites, '... but not in the city, and he does not return it in the city.'

Nimukei Yosef (DH Kosav): The Rif connotes that he need not begin in the field, in order that he will not need to finish in the city. Rashi connotes similarly. Since the question was not settled, he need not begin, but if he began, he must finish even in the city, like one who hit an animal. The Rambam obligates a full return. It seems that he explained (the question) like Rashi. It seems that the scribe erred and wrote 'he does not return.' The text of the Rif should say 'he returns', like the Rambam. Since it is clear that if he began, he must finish, and it is a Safek mid'Oraisa whether he must begin, we should say that he begins, for this is the Mitzvah of a Chacham that it is below his dignity, just like one who saw his Aveidah and it is worth more than his friend's (he may opt to do the Mitzvah to save his friend's).

Beis Yosef (CM 263 DH Kosav Nimukei): The Nimukei Yosef never considered that the Rif could have a different text. He assumed that he had our text, which requires full return, or totally exempts. This forced him to explain that the Rif totally exempts. If so, the Rif should have simply said 'he does not return.' Why did he add 'in the city?' Rather, the Rif's text was like the Rosh said.

Rambam (Hilchos Gezeilah 11:13): If a dignified Chacham found a bag or box, and he does not normally carry such Kelim in his hand, he is not obligated to deal with it. If he would normally return such Kelim in a field, but not in the city, if he found them in the city, he need not return them. If he found them in the field, he must return them to the owner's premises, even though it is in the city and normally he does not carry them there.

R. Akiva Eiger (Teshuvah 1:193 DH v'Nir'eh): This is like Tosfos (25b DH v'Im), who says that Rabah obligates only for animals, for he caused them to stray. This is in the city, where he does not become a Shomer Aveidah for other things. In the field he must return everything (at least until the city), and since he became a Shomer Aveidah, he cannot leave it, and must fully return it.

Rosh (Bava Metzia 2:21): If a Chacham found an Aveidah in a field, which normally he would carry in a field but not in the city, since he is exempt from a full return, perhaps he is totally exempt. The Gemara never settled the question. Some say that we are stringent, and he is obligated. I say that since the Torah exempted him, for he should not disgrace his honor, it is forbidden to him, for he belittles the honor of Torah where there is no obligation. The Rif said that the Gemara did not resolve this question; and he does not return it in the city. It seems that his text of the Gemara said 'perhaps in the field, in any case, he must return it. Or, a full return is required, and since he is not obligated in the city, he is not obligated even in the field.' He rules stringently, and requires returning in the field, for there he does not disgrace his honor. This is unlike 'if the Chacham hit the animal, he is obligated to return it.' There, he caused it to stray (and it is less likely to return home). Here, he brought it to (just outside the city,) a place more guarded than where he found it.

Question (Lechem Mishneh 11:13 and Gra CM 263:2): If this was the Rif's text, why did the Rif say 'therefore he does not return in the city'? There was no Hava Amina to return in the city!

Answer (Lechem Mishneh): The Rif's text said that surely he must return in the field. The question was whether he must return in the city. He concluded that he does not, for this would disgrace his honor.

Poskim

Shulchan Aruch (CM 263:2): (If a dignified Chacham found a bag or box, and he does not normally carry such Kelim in his hand...) if he would normally return such Kelim in a field, but not in the city, if he found them in the city, he need not return them. If he found them in the field, he must return them until reaching the owner's premises, even though it is in the city and he normally does not carry them there.

Beis Yosef (DH veha'Rambam): The Rambam holds that since the question was not settled, we are stringent and obligate a full return.

Rema: Some say that he does not return in the city. He just brings them from the field to the city, and leaves them.

Rebuttal (Beis Yosef DH v'Chosav): The Tur said that this is the Rosh's opinion. This is wrong! The Rosh's text of the Gemara said that either he is totally exempt, or he is totally obligated!

Defense #1 (of Tur - Darchei Moshe 1): The Rosh holds that the exemption is because it disgraces the honor of the Chacham's Torah. Surely he is liable to return in the field, when no one sees and there is no disgrace, even though he need not return in the city!

Hagahos Prishah (1 and Drishah 1): The Gemara said that either the law of the city is drawn after that of the field, or vice-versa. Since the question was not resolved, we must be stringent as long as there is no Isur in our stringency. The Gemara asked whether the Torah obligates fully returning. If it does, we are not concerned for disgrace. There is no disgrace in doing a Mitzvah! Even though the Rosh connotes that one returns it only until the city only according to the Rif's text, the Rema must explain that what is logically reasonable according to our text, is clear from the Gemara according to the Rif's text. However, Tur cites in the name of the Rosh the opinion that fully obligates, and says 'just the opposite!' I.e., he is totally exempt (according to our text). The Tur holds that the Rosh prefers the opinion and text of the Rif, for he brought it last.

Defense #2 (of Tur - Taz DH Ela): If the exemption is only due to disgrace, and this is only in the city, once we obligate in the field, he should need to return even in the city! It seems that there is a Mitzvah to return it in the field (to just outside the city) since it is guarded better there than in the field, like the Rosh says according to the Rif, so he does this return beyond the letter of the law. This answers the Beis Yosef's question. Had the Rif concluded this way from his own reasoning, he would have mentioned the Isur to return when one is exempt, like the Rosh mentioned. Rather, the Rif merely rules that one is exempt (in the city), not that there is an Isur to return.