Resources and Review Tests for Nedarim 52
The גמרא says that if you made a food אסור on yourself with a נדר and it gets mixed in with other food, it is בטל שישים. The ר"ן very famously asks why this isn’t a case of דבר שיש לו מתירין which is never בטל? He answers with a new concept which is also a major חידוש להלכה: the notion of דבר שיש לו מתירין only applies where there is a conflict of sorts. The logic is as follows: רבי יהודה says מין במינו isn’t בטל because like things do not dilute one another. In fact, they make each other stronger. The חכמים who disagree just hold that since one is איסור and one is היתר, they are not in the halachic sense truly the same and hence they can be subject to ביטול. However, there are many nuances. If two of the exact same item are in a sense both מותר such as in our case where the דבר הנדור is a דבר שיש לו מתירין since he can be שואל על נדרו, then מדרבנן we view it as if its already מותר and hence there is no conflict between the items and there cant be ביטול. However, if they are two physically different items then there is enough conflict for ביטול to take place. Nonetheless, if the two items are both fully מותר such as in the case of an item which cant be moved out of one תחום which gets mixed with something that cant be moved from another תחום, then even if they are both physically different there isn’t enough of a conflict and there cant be ביטול.
This פּשט of the ר"ן is on contrast to רש"י in ביצה דף ג׳ ע"ב ד"ה אפילו who says that the concept of דבר שיש לו מתירין is simply that if one can make something מותר why eat it with ביטול? There is an incredible תשובה in the באר יצחק in יו"ד סימן י who asks a lot of questions: first, the ר"ן is based on the fact that רבי יהודה holds that מין במינו isn’t בטל. But the נודע ביהודה says that even רבי יהודה holds that this is only true by liquid items. However, if three pieces of meat get mixed up and two are slaughtered and one is not, everyone agrees it is בטל ברוב. According to the ר"ן, how can this be? There is no conflict there so why should it be בטל? Secondly, many אחרונים including the רש"ש and פּני יהושע ask on the ר"ן from the גמרא on דף ד in ביצה which says that ספק דבר שיש לו מתירין is אסור even by a ספק דרבנן. According to רש"י, that makes perfect sense since why eat something that might be אסור if you can eat it when it becomes מותר? But according to the ר"ן, the whole issue is a problem with ביטולand there is not ביטול going on there so why should it be more חמור? Third, how can רש"י say that when an item becomes בטל בשישים it cannot be eaten because better to eat when it becomes מותר—it already is מותר since its בטל שישים! Finally, he asks the question brought by רבי עקיבא איגר in שולחן ערוך יו"ד סימן צ"ט סעיף ו who asks that the משנה in כלאים says that camel wool can be בטל in sheep wool such that it can be sown with linen. Those are both מותר items so according to the ר"ן, if there is no conflict, how can it be בטל? He answers with a wonderful תירוץ: רש"י and the ר"ן really don’t argue at all. רש"י is in ביצה discussing eggs and wood chips and the like, all of which are solids. The ר"ן is discussing liquids where ביטול בשישים is relevant. The ר"ן agrees that when it comes to solids you needs רש"י’s פּשט. And in the case of solids, the three pieces don’t become fully מותר as you aren’t allowed to eat all three pieces. We just allow you to pick one and assume it’s מותר because of רוב. So we are מחמיר בספק there since its better to eat it when its really מותר. By liquids, even רש"י needs the ר"ן since if its בטל it really is מותר, so the issue must be a problem with the ביטול itself. He says that this also answers רע"א’s question since everyone agrees by solids that they are בטל, including by wool. רש"י doesn’t apply there as well since it is מין באינו מינוand the ט"ז in סימן ק"ב says that if it will be נקרא על שם ההיתר it is מותר.
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