Resources for Nedarim 78
The גמרא says that you need three הדיוטות to be מתיר נדרים if you don’t have a חכם. The גמרא never gives a clear source for the requirement of the number three—it just says that you are allowed to use three הדיוטות. The ר"ן says that since we know you need more than one we assume three because its כעין ב"ד. The רא"ש says that it must be three people because if it was just two then it would be a ב"ד שקול and that is פּסול for a ב"ד. He adds that even according to שמואל who says שנים שדנו דיניהם דין, that is only by דיני ממונות but not by איסור והיתר. It seems that you need a real דין ב"ד. There is a תשובות רבי עקיבא איגרin סימן ע"ג who was asked if a 15 year old boy could be part of a ב"ד to be מתיר נדר since he wasn’t מתמלא זקנו in which case we only know he is a גדול from חזקה דרבה which is not valid by a דין דאורייתא. He answered that he could be part of the ב"דbut there needed to be three others and he would be the 4th. But how can a ב"ד have 4? Wouldn’t that be an issue of a ב"ד שקול? This question is asked by רב יצחק אלחנן זצ"ל in נחל יצחק חו"מ סימן ג ס"ג. The נחל יצחק also says that some have the custom to try to do התרת נדרים in front of 10 an that is also an issue of a ב"ד שקול. The משנת יעב"ץ in או"ח סימן נ"ג suggests that perhaps a ב"ד of four or six is כשר לכתחילה since once you have a שיעור of a minimum ב"ד then you can add any amount. His proof is the גמרא in הוריות דף ג ע"ב that discusses a case of “מאה שישבו להורות” so you see that an even number of people can be a ב"ד. This also seems to be the שיטת הרמב"םin הלכות סנהדרין פּרק ב הל י"ג who says the bigger the ב"ד the better since its better to have the דין paskened by 11 then 10. Sounds like 10 can be a ב"ד as well.
In a related topic, there is a מחלוקת ראשונים whether the אחד מומחה needs to be a סמוך or not. The רמב"ן quoted by the ר"ן says that the person needs to be a סמוך whereas the ר"ן himself disagrees and says you don’t need to be a סמוך. The requirement to be a סמוך sounds related to the concept of needing a real concept of ב"ד which would fit well with the רא"ש whereas not needing a סמוך would fit better with the ר"ן who לשיטתו does not seem to need a full דין ב"ד. It should be noted that רע"א in the תשובה quoted above points out that relatives are כשר for התרת נדרים, and you can do it standing and at night which is not allowed in a typical ב"ד setting. However, those are cases where the people can be כשר for others or at other times, but people who are truly פּסול a פּסול הגוף cannot be part of התרת נדרים either.
The גמרא discusses שאלה בהקדש. That means that if you are מקדיש something you can go to the Rav and undo your הקדש. This also means that if you did שחוטי חוץ you can get out of the חיוב כרת by being שואל על ההקדש. Is there ever a time you lose that היתר? Can you be שואל on it while the כהן is eating it? תוספות in כריתות דף י"ג ע"ב ד"ה וארבע says that once the blood is sprinkled you stop being the בעלים and at that point you can’t be שואל on it anymore.
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