Resources and Review Test for Nedarim 58
The גמרא says that שביעית will be אוסר במשהו because of the principle of דבר שיש לו מתירין. The גמרא then qualifies that this is talking about ביעור, but for אכילה it would have regular דיני ביטול. The ר"ן explains that we are talking about either an onion planted originally in the sixth year and then uprooted and replanted again in the שמיטה year or a regular mixture of פּירות שמיטה and regular fruit. The case where it is considered דבר שיש לו מתירין is where the mixture occurred before the time of ביעור. If you left that mixture hanging around until after the time of ביעור it would be אוסר במשהו because you could have eaten it earlier בהיתר. This is an unusual type of דבר שיש לו מתירין. As we know, there are two explanations for דבר שיש לו מתירין. רש"י in ביצה דף ג׳ ע"ב says that the reason דבר שיש לו מתירין is אסור במשהו is because of the concept of “עד שתאכלנה באיסור, תאכלנה בהיתר”, which basically means why eat איסור for no reason. However, in our case, “that ship has already sailed”. It’s too late now so it is a חידוש to say don’t eat it when at this point there is nothing I can do about it. It is even a bigger חידוש like the ר"ן in נדרים דף נ"ב. The ר"ן there had said that the reason דבר שיש לו מתירין is אסור במשהו because nothing can be מבטל itself (מין במינו אינו בטל) so if the two items are identical then there is no ביטול. Normally one is אסור and one is מותר but if in some sense we view one as היתר then it cant be בטל at least מדרבנן. In our case, to view it now after ביעור as היתר because a month ago I could have eaten it בהיתר seems like a significant חידוש.
There is another חידוש in our ר"ן as well. The רמ"א inיו"ד סימן ק"ב סעיף ד says that anything where the איסור is born בתערובות is not an issue of דבר שיש לו מתירין. For example, if you squeeze grapes before Shabbos into a bowl and leave them there over Shabbos and they continue to drip out juice on שבת (that juice is אסור on Shabbos), we do not say that the juice that came out on Shabbos is אסור במשהו because of דבר שיש לו מתירין (you can just wait till after שבת to drink it) since the איסור was נולד בתערובות. The הגהות רע"א there points out that our ר"ן must not hold like that since in our case of an onion that grew some in the seventh year, the איסור was נולד בתערובות.
It is important to note that there is a מחלוקת ראשונים as to what ביעור is. The רמב"ם in הלכות שמיטה ויובל פּרק ז הל׳ ג says it needs to be destroyed. The רמב"ן in ויקרא פּרק כ"ה פּסוק זsays it just means you need to make it הפקר and a minute later you can reacquire them. However, if you fail to be מפקיר then the פּירות become אסור.
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