2) A FIRSTBORN'S RIGHT TO DECLINE THE DOUBLE PORTION WHILE HIS FATHER IS ALIVE
OPINIONS: The Mishnah states that when one stipulates that "my firstborn son shall not inherit the double portion," his stipulation is not valid because it conflicts with the law of the Torah which entitles the Bechor to a double portion. The Gemara asks that this stipulation is one concerning a monetary matter, and such a stipulation is binding even when it conflicts with the law of the Torah. The Gemara answers that such a stipulation is binding only when it may be assumed that there is consent on the part of all of those who are affected by the stipulation. In this case, it cannot be assumed that the Bechor consents.

This seems to imply that if the Bechor explicitly expresses his consent, then he indeed relinquishes his right to his double portion. Does this mean that a Bechor may relinquish his right, during his father's lifetime, to receive the double portion of inheritance after his father dies?

(a) The RASHBAM (DH Hasam Ka Machlah) writes that the reason why the father's statement is not binding in this case is that the silence of the Bechor is not considered consent; he remains quiet merely in order to avoid angering his father. He does not have any intention to forgo his double portion. The Rashbam's words imply that if the Bechor explicitly consents to forgo his double portion, then his consent is valid and he does not receive the double portion.

The OR ZARU'A suggests that the Rashbam maintains that only a Bechor can forgo his double portion, but an ordinary son cannot forgo his portion. This is because the Torah refers to the Bechor's double portion as a "gift" (see Insights to Bava Basra 124:1). Since a person is entitled to decline a gift, the Bechor is entitled to decline the double portion. An ordinary heir, in contrast, cannot decline his share, because doing so would be counter to the Torah's law of Yerushah. (See also KOVETZ SHI'URIM #403.)

The KETZOS HA'CHOSHEN (278:13) explains that, according to the Rashbam, the Bechor's right to forgo his double portion applies not only when his father says that he does not want the Bechor to receive the double portion, but even when the Bechor, on his own initiative, declares that he does not want the double portion. This is because the mechanism by which the Bechor is able to forgo his double portion is through Mechilah; a person can be Mochel and forgo something that he is entitled to receive. The NESIVOS HA'MISHPAT, on the other hand, explains that the Bechor cannot forgo his double portion; the Torah requires that he receive it as an inheritance. Only when the father of the Bechor says that he does not want the Bechor to receive the double portion, and the Bechor consents, does the Bechor not receive the double portion. This is because the father has the right to re-direct the inheritance to any of his heirs. Even though the Torah prohibits him from re-directing the double portion away from the Bechor, when the Bechor consents the Torah's prohibition is removed and the double portion can be re-directed by the father. When the father does not re-direct the double portion, though, and the Bechor declares that he wishes to forgo the double portion, he cannot forgo the double portion that the Torah gives him.

(b) The RASHBA and other Rishonim argue and maintain that a Bechor cannot forgo his right to the double portion while his father is alive. The Torah gives the property to the Bechor when his father dies, and until that time there is nothing that the Bechor can do to stop the Torah's law from taking effect.

(The RAMAH explains that the son's right to receive the inheritance comes at the moment that he is born. At that moment, he did not renounce that right, and thus the Torah's law takes effect and he receives the Yerushah and he cannot decline it.)

The Rashba adds that the Gemara, when it says that the Bechor did not consent, does not mean that if he did consent his consent would be valid. Rather, the Gemara means that the Bechor cannot consent to forgo his double portion, and even if he does consent, his consent is not valid. This is also the explanation of the NIMUKEI YOSEF here (see also TOSFOS to Kesuvos 56b).