Resources for Nedarim 17
1. The משנה says that is one make a שבועה to not eat an apple and then makes the exact same שבועה again, the second שבועה is not חל. The דבר יעקב points out the following: there is a three way מחלוקת ראשונים as to why the שבועה is not חל. The ר"ן says its not חל because the person is already מושבע ועומד. The רא"ש says the reason is because a שבועה can only be חל on something optional (איתא בלאו והן) and since this person already has an obligation to not eat the apple, the שבועה is not valid. תוספות says that the reason the second שבועה is not חל is because of אין איסור חל על איסור. There is an important אבני מילואים in שו"ת סימן י"ב which is very relevant to our סוגיא. He brings a ש"ך in יו"ד סימן רל"ה ס"ק א who says that a person who made a שבועה to not eat נבילה and then becomes a חולה שיש בו סכנה who is now allowed to eat נבילה, doesn’t need to try to get a התרה for his שבועה since the first שבועה was never חל anyway. The פּרי מגדים in his פּתיחה להלכות פּסח disagrees with this because he says that reason the second שבועה was not חל is because of the reason תוספות said of אין איסור חל על איסור. Consequently, the second איסור is not totally invalid. After all, the גמרא in יבמות דף ל"ב ע"ב says that אין איסור חל על איסור doesn’t mean the איסור is not there but only that there is no מלקות במזיד or חטאת בשוגג. The נפקא מינה is that the person who violates the double איסור will get buried amongst רשעים גמורים. The פּרי מגדים says that another נפקא מינה is this case! If the original איסור נבלה goes away then the שבועה should come back! This מנחת שלמה suggests that this is exactly the reason the רא"ש (and ר"ן) did not say תוספות’s explanation of אין איסור חל על איסור—he agreed with the ש"ך that the איסור is completely gone.
The אבני מילואים suggests that everyone should agree that the concept of אין איסור חל על איסור exists by שבועה. However, as the פּמ"ג said, that would leave the שבועה still intact, just without a חיוב מלקות. The concept that the ר"ן mentions of מושבע ועומד מהר סיני tells us that the נדר cannot be חל at all since he had no capability to make it. The קובץ הערות in סימן ל"ג אות ב has a different approach which is לשיטתו. He says that אין איסור חל על איסור does not apply to שבועה. The reason is that the fact that a person can’t eat נבילה is because the תורה says they may not eat it. The fact that one swore to not eat it has nothing to do with the act of eating the נבילה—the איסור is not to be מחלל your words in whatever form that takes. Therefore, you cant apply the principle of אין איסור הל על איסור. While he does not speak this out explicitly, it should come out that in our case as well where someone swore twice to not eat the same apple, if one spoke twenty times, one has twenty sets of words to not be מחלל.
2. As mentioned above, if a person makes a שבועה twice to not eat the same apple, the משנה says the second שבועה is not valid. The ריטב"א on the beginning of the next דף says that if a person makes this שבועה twice he gets מלקות anyway because it is a שבועת שוא (no purpose)! The רמב"ם in הלכות שבועות פּרק ד׳ הל׳ ט does not seem to agree with this and holds there is no מלקות at all. The מנחת שלמה points out that the ריטב"א must hold like the ש"ך mentioned above that there is no איסור created by the second שבועה or else it would not be considered “שוא” as it adds a second איסור.
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