Keep Thy's Word

The Gemorah in Nedarin (2b) says that an issur neder is an issur cheftzah.  The Ran and Rosh disagree if the Gemorah is teaching us the nature of neder or the terminology of neder is expressed as an issur on the cheftzah.  The question is neder purely an issur cheftzah or is there an element of issur gavrah as well?

The source for such an idea that it may be an issur gavrah would seem to stem from the language of the possuk, אִישׁ֩ כִּֽי־יִדֹּ֨ר נֶ֜דֶר לַֽי״י֗ אֽוֹ־הִשָּׁ֤בַע שְׁבֻעָה֙ לֶאְסֹ֤ר אִסָּר֙ עַל־נַפְשׁ֔וֹ לֹ֥א יַחֵ֖ל דְּבָר֑וֹ כְּכׇל־הַיֹּצֵ֥א מִפִּ֖יו יַעֲשֶֽׂה.  The issur is described as a desecration of the person’s speech. 

The Minchas Chinuch (368:4) assumes in a situation where a person accepts upon himself nezirut for less than 30 days or for only one of the prohibitions of nezirut, where he is established as a complete nazir for 30 days, that there is no violation of בל יחל because the Torah imposed upon him the additional stringencies but he never accepted it upon himself.  He clearly assumes that the issur is to violate one’s word, not the cheftzah of the neder. 

The Rambam (Laws of Nedarim 10:12) holds that if one forbids person B from receiving benefit from him and then person B benefits, it is person A, that made the neder that gets the punishment.  The Ran (Nedarim 15a bottom,) disagrees, and holds it is person B who gets punished for they violated the neder.  Clearly, the Ran holds the issur is to violate the cheftzah of the neder, not the violation of one’s word, not like the Minchas Chinuch.  However, the Rambam holds it is upon the one taking the neder to make sure his/her word is upheld.  He may hold like the Minchas Chinuch but we aren’t forced to say so.  He may hold the one who made the neder is the one responsible for it, but his/her responsibility isn’t limited to what was only explicitly stated in his/her neder.