Ran:
https://dafyomi.co.il/nedarim/tosfos/nd-ts-018.htm
Ran proves that Neder trumps Shvua, but how can he (seemingly) ignore the gemara's position -- on this page -- that Shvua is stronger than Neder (https://www.sefaria.org/Nedarim.18a.6?lang=bi&with=all&lang2=en)?
Paul Davidowitz, Long Beach
Great to hear from you. I had not thought about this question before.
The passage of the Gemara which you cite is actually the proof that the Ran adduces to prove his Yesod. He observes that even though a Shevu'ah is in some ways more stringent than a Neder, (e.g. it can be Chal on a Davar she'Ein Bo Mamash (e.g. sleep) and also it is "not cleansed" of punishment), nevertheless in another application a Neder has more ability to be Chal than does a Shevu'ah, for example on a Mitzvah. The Ran explains that the principle behind that is because a Neder is an Isur Cheftza [and Gavra] whereas a Shevu'ah is [only] an Isur Gavra. For this very reason, says the Ran, a Neder can apply on top of a Shevu'ah, but not vice versa.
Best wishes,
Yishai Rasowsky