Another difference between nedarim and shevuot is whether you can make two nedarim or two shevuot on the same thing. The Mishna on our daf teaches that this cannot be done in the case of shevuot, but it can take place in the case of nedarim. The example presented by the Mishna is a person who says, “If I eat I will become a nazir,” and then repeats the same statement a second time. In such a case of a vow within a vow, once the person eats he is obligated in nezirut twice.
There are two approaches to this rule about neder.
Tosafot, the Ran and others argue that it is only in the case of nazir that a neder will take effect twice. In other cases, once a person has declared an object to be forbidden it cannot become “more forbidden” by the person’s statement. According to this approach, the unique status of nezirut stems from a gezeirat ha-katuv – a passage in the Torah – nazir le-hazir, which is understood by the Gemara to teach this law. Furthermore, nazir is unique in that the two obligations of nezirut will take effect one after another, unlike ordinary cases of neder where the prohibition would need to affect the object twice in the same way.
The Ritva and Rabbi Avraham min HaHar follow the Rambam in arguing that the Mishna means that all cases of neder have this rule. Therefore, if a person states two times that a given object is forbidden to him as a neder – and then eats it – he will be liable for two sets of punishment for breaking his word. This works because of the parallel between neder and korban, which we have noted in the past. Just as a person can obligate himself to bring repeated sacrifices similarly when he says, “This object is to me like a korban,” it will take effect more than once. The Ritva explains that the Mishna chose the example of nezirut not because of its unique status, but because the source for this law – the repetition of the words nazir le-hazir – appears in that specific case.