Q: In what cases does minhag hamedina take precedence over Torah law?
A: We mentioned last week that minhag hamedina is a fundamental principle in monetary law, and in certain cases the common commercial practice supersedes the default halachah (Radbaz #545; Pischei Teshuvah 333:8).
This is because in most contractual monetary issues, the parties can agree to whatever binding terms they want. A community, as well, can establish monetary guidelines that are binding, as a matter of convention (C.M. 231:27-28).
Therefore, minhag hamedina applies only in cases that the parties can contractually agree, but it cannot uproot Torah law on issues that are not contractual.
Therefore, regarding the laws of inheritance, ribbis or ona’ah (unfair pricing), which entail absolute halachic rules and prohibitions that the parties cannot agree upon to violate, minhag hamedina cannot undo Torah law (Y.D. 160:1; C.M. 227:1; Rema 281:4).
However, regarding monetary obligations that the parties can obligate themselves through a kinyan – minhag hamedina can establish this obligation.
