each to the other.

The Gemara questions this ruling: Whichever way you look at it, Shmuel’s opinion is difficult. If he holds in accordance with the opinion of the Rabbis with regard to this issue, he should have sent them a response in accordance with the opinion of the Rabbis, and if he holds in accordance with the opinion of Rabbi Yehuda, he should have sent them a response in accordance with the opinion of Rabbi Yehuda. Shmuel’s response is not in accordance with either tannaitic opinion.

The Gemara answers: He is uncertain whether the halakha is in accordance with the opinion of Rabbi Yehuda or in accordance with the opinion of the Rabbis. Therefore he sent them a response that incorporates both opinions.

The Gemara explains: What is the dispute between Rabbi Yehuda and the Rabbis? As it is taught in a baraita: Expounding the verse: “He shall acknowledge the firstborn” (Deuteronomy 21:17), the Sages said: He shall acknowledge him to others. In other words, a father is deemed credible to tell others that this is his firstborn.

From here, Rabbi Yehuda says that a man is deemed credible to say: This is my firstborn son, even if he has sons presumed to be older. And just as a man is deemed credible to say: This is my firstborn son, so too, a man who is a priest is deemed credible to say about his son: This is a son of a divorced woman, or: This is a son of a yevama who has performed ḥalitza [ḥalutza], in which cases he is disqualified from the priesthood due to his flawed lineage [ḥalal]. And the Rabbis say: He is not deemed credible.

Rav Naḥman bar Yitzḥak said to Rava: Granted, according to Rabbi Yehuda, this is the reason that it is written: “He shall acknowledge;” he derives from these words that a father is deemed credible to attest to the identity of his sons. But according to the Rabbis, why do I need the term “he shall acknowledge”?

The Gemara answers: It is necessary for a case when he requires identification, i.e., when there is no presumption as to the identity of the firstborn. In such a situation the verse teaches that the father is deemed credible. The Rabbis disagree with Rabbi Yehuda’s opinion only in a case where another son is presumed to be the firstborn.

The Gemara asks: According to the Rabbis, with regard to what halakha is it necessary for the verse to teach that a father’s identification of his firstborn is deemed credible? If it is with regard to giving him a double portion, it is superfluous. Let the son be only like another person, i.e., one who is not an heir; if the father wants to give him a double portion of his estate as a gift, can he not give it to him? Since the father can give a double portion to the firstborn without having to testify that he is his firstborn, it cannot be that the verse is teaching us that he is deemed credible with regard to the halakha that a firstborn receives a double portion.

The Gemara answers: No, it is necessary with regard to property that came into the father’s possession afterward, after he testified that his son is his firstborn. He could not have given him this property as a gift, as at the time of his testimony, the property did not yet belong to him, and one cannot transfer ownership of an item that one does not own. Therefore, it is necessary for the verse to teach that the father’s testimony is deemed credible so that the son can receive a double portion of the father’s future property as well.

The Gemara asks: And according to Rabbi Meir, who says that a person can transfer an entity that has not yet come into the world, which would mean that one can give away his property even before it enters his possession, why do I need the term “he shall acknowledge”?

The Gemara answers: The term is necessary for a case where property came into the father’s possession when he was moribund, at which point he cannot transfer ownership of any of his property to others. It is with regard to such property that the verse states: “He shall acknowledge,” to teach that the son who the father states is the firstborn will receive a double portion even of that property.

The Sages taught in a baraita (Tosefta 7:3): If the court had a presumption concerning a son that he is a firstborn, and his father said concerning another son of his that he is his firstborn, the father’s statement is deemed credible. If the court had a presumption concerning a son that he is not a firstborn, and his father said that he is his firstborn, the father’s statement is not deemed credible.

The Gemara asserts that as the two halakhot of the baraita seem to contradict each other, it must be that the first clause represents the opinion of Rabbi Yehuda, and the latter clause represents the opinion of the Rabbis.

§ Rabbi Yoḥanan says that if one says about another: He is my son, and then says: He is my slave, his latter statement is not deemed credible. It cannot disqualify him from marrying a Jewish woman or exclude him from his inheritance. Conversely, if he first says: He is my slave, and then says: He is my son, his latter statement is deemed credible, as in his first statement he presumably was saying: He serves me as a slave does.

And the opposite halakha applies to one at the tax house: If one is passing the customs house and says about a certain person: He is my son, and then later says: He is my slave, his latter statement is deemed credible, as he presumably says that the other is his son only to evade paying a tax for possessing a slave. Conversely, if he says at the customs house: He is my slave, and then later says: He is my son, his latter statement is not deemed credible, as one would not unnecessarily render himself liable to pay a tax.

The Gemara raises an objection from a baraita: If one was serving another person like a son serves his father, and the person being served came and said: He is my son, and then said: He is my slave, his latter statement is not deemed credible. Additionally, if one was serving another person like a slave serves his master, and the one being served came and said: He is my slave, and then said: He is my son, his latter statement is not deemed credible. This contradicts Rabbi Yoḥanan’s statement that if he first says that he is his slave and then says that he is his son, his latter statement is deemed credible.

Rav Naḥman bar Yitzḥak said: There, in Rabbi Yoḥanan’s statement, it is a case where he is presumed to be a slave because everyone calls him: A slave on whose border [metzar] are one hundred. Since everyone is referring to him in this manner, the person he served cannot call into question his status as a slave by saying that he is his son. The Gemara asks: What does it mean that on his border [metzar] are one hundred? The Gemara answers: One hundred dinars are adjacent to [metzar] this slave. In other words, he is worth one hundred dinars.

§ Rabbi Abba sent several rulings from Eretz Yisrael to Rav Yosef bar Ḥama, including the following: In the case of one who says to another: You stole my slave, and he says in response: I did not steal him, and when the first inquires: If so, what is the nature of his presence in your possession, the latter responds: You sold him to me,