The Mishna on our daf teaches about a case where a son can shave (i.e. cut off his hair following nezirut) based on his father’s nezirut: ha-ish megale’ah al nezirut aviv. The Mishna explains that the case is where the father was a nazir and set aside money for his end-of-nezirut sacrifices without specifying which they were for, but he died before completing his nezirut. Should his son say, “I accept upon myself nezirut, and will use his money for my sacrifices,” he is allowed to do so.
Rabbi Yosei argues that in such a case, the money cannot be used by the son, and must go instead to voluntary sacrifices. He suggests that the case of ha-ish megale’ah al nezirut aviv is when a father and son are nezirim together, and the father set aside money to pay for the sacrifices that he needs to bring upon completing his nezirut without specifying which korbanot they are for. In such a case, if he dies before the period of nezirut is over, his son can make use of the sacrifices for himself.
The explanation for this appears to be that in the first case, according to Rabbi Yosei, there is no connection whatsoever between the nezirut if the father and the son, since the son’s nezirut begins only after the father’s has ended. In the second case, however, the fact that father and son are experiencing nezirut together allows the son to make use of his father’s money.
There is an alternative reading to this Mishna, which offers a diametrically opposite approach to the case of ha-ish megale’ah al nezirut aviv. According to the alternative reading, all agree that in a case where the father and son are nezirim at the same time, the son can use his father’s money for the sacrifices. The argument is in the case where the son accepts nezirut in the wake of his father’s death. The explanation according to this reading is that when the father and son are nezirim at the same time, the son has an independent obligation and cannot use his father’s money. When he accepts nezirut and states that it will be based on his father’s obligation, he has the right to do so.