Why must the verse state: “He may not make the son of the beloved the firstborn” (Deuteronomy 21:16)?

Abba Ḥanan explains: It is necessary because it is stated previously in the verse: “Then it shall be, in the day that he causes his sons to inherit,” as one might have thought: Could this not be derived through an a fortiori inference, as follows: And if with regard to an ordinary son, one who is not a firstborn, whose power is enhanced in that he takes in inheritance the property due the deceased as he does the property the deceased possessed at the time he died, nevertheless, the Torah gave the father permission to bequeath his estate to whichever of his sons he wishes, depriving his other sons of their portions, then with regard to a firstborn, whose power is diminished in that he does not take a double portion of the property due his father as he takes of the property the deceased possessed at the time of his death, is it not clear all the more so that his father can deprive him of the double portion he receives as a firstborn? Therefore, the verse states: “He may not make the son of the beloved the firstborn.”

Abba Ḥanan continues: And let the verse state only the prohibition of: “He may not make the son of the beloved the firstborn.” Why must the verse state: “Then it shall be, in the day that he causes his sons to inherit”?

It is necessary because one might have thought: Could this not be derived through an a fortiori inference, as follows: And if with regard to a firstborn, whose power is diminished in that he does not take a double portion of the property due his father as he takes of the property the deceased possessed, nevertheless the Torah states: “He may not make the son of the beloved the firstborn,” i.e., the firstborn may not be deprived of his double portion, then with regard to an ordinary son, whose power is enhanced in that he takes in inheritance the property due the deceased as he does the property the deceased possessed, is it not clear all the more so that his father cannot deprive him of his portion of the inheritance?

Therefore, the verse states: “Then it shall be, in the day that he causes his sons to inherit,” indicating that the Torah gave the father permission to bequeath his estate to whichever of his sons he wishes. Consequently, the prohibition “he may not make the son of the beloved the firstborn” is not available to prove that one may bequeath his estate to whichever of his sons he wishes.

§ The Gemara resumes discussion of the halakhic ruling: Rabbi Zerika says that Rabbi Ami says that Rabbi Ḥanina says that Rabbi Yehuda HaNasi says: The halakha is in accordance with the opinion of Rabbi Yoḥanan ben Beroka. Rabbi Abba said to Rabbi Zerika: It was stated that Rabbi Yehuda HaNasi ruled in an actual case in accordance with the opinion of Rabbi Yoḥanan ben Beroka.

The Gemara asks: With regard to what principle do they disagree? Since both Rabbi Zerika and Rabbi Abba agree that the halakha is in accordance with the opinion of Rabbi Yoḥanan ben Beroka, why did Rabbi Abba state that Rabbi Yehuda HaNasi ruled as much in an actual case? The Gemara answers: One Sage, Rabbi Zerika, holds that a ruling in principle is a preferable source for a halakha, rather than a ruling from an incident; and one Sage, Rabbi Abba, holds that a specific incident ruled upon by a Sage is a preferable source.

The Gemara examines which source is preferable. The Sages taught in a baraita: One may derive the halakha neither from a statement nor from an incident where one saw a ruling issued in a certain manner, unless the Sages explicitly tell him that it is the practical halakha. If he asked the Sages and they told him the practical halakha, he may go and act upon the ruling in those circumstances, provided that he does not compare between cases and apply the ruling to other circumstances.

The Gemara asks: What is the meaning of the statement: Provided that he does not compare? But don’t we compare cases throughout the entire Torah? The main method of halakhic derivation is through comparing cases where the halakha was already established to cases where the halakha is unclear.

Rav Ashi said that this is what the baraita is saying: Provided that he does not compare between various cases of animals with wounds that will cause them to die within twelve months [tereifot], which are forbidden for consumption. In general, one may compare cases, but with regard to the definition of a tereifa, one may not compare.

This is as it is taught in a baraita: With regard to tereifot, one does not say: This wound is similar to that wound. Every type of wound has its own halakhot. And do not wonder about this principle, as there are organs with regard to which one cuts it from here, i.e., one side, and the animal dies within twelve months, but one cuts it from there, i.e., another side, and it lives.

Rabbi Asi said to Rabbi Yoḥanan: When the Master, i.e., Rabbi Yoḥanan, says to us: This is the halakha, should we act upon the ruling? Rabbi Yoḥanan said: Do not act upon the ruling unless I say that it is a practical halakha.

Rava said to Rav Pappa and to Rav Huna, son of Rav Yehoshua: When a legal ruling of mine comes before you and you perceive a refutation of it, do not tear it up until you come before me to discuss it. If I have a valid explanation, I will tell you, and if not, I will retract my ruling. If a ruling of mine comes before you after my death, when you can no longer discuss it with me, do not tear it up, but do not learn from it either, i.e., do not rule in accordance with it. Do not tear it up, as had I been there, perhaps I would have told you a valid explanation that you would have accepted;