The gemara on Bechoros 49b clearly infers that Pidyon HaBen is an issue of issurim and we would pasken like Rav normally, but here we make an exception. Why is Pidyon HaBen more of an issur issue rather than a din or mamon issue?
Aharon Levine, Baltimore, Maryland, USA
Tosfos in Kidushin (23b, DH "v'Rebbi Elazar") quotes an important Yesod regarding how to determine when a Machlokes Rav and Shmuel is one of Isur or Mamon when it affects both. Rabeinu Tam says that if the argument is about Isur, then it is one of Isur, even if it affects Mamon (and visa versa). Accordingly, in our Gemara where the argument is about the Torah's directive to redeem a Bechor once he has reached thirty days and therefore, whether or not he is redeemed, it follows that the argument is one of Isur (as probably most arguments regarding Pidyon ha'Ben would be classified according to Rabeinu Tam).
Kol Tuv,
Yaakov Montrose