Resources for Kesubos daf 15
1. The משנה says that if רוב אנשי העיר are כשר then she can marry a כהן. רבי עקיבא איגר on our משנה says a fascinating חידוש which is an important יסוד: if there are 51 כשר men in the town and 50 פּסולים (which means רוב are כשרים ), then if one of the 51 כשרים are a כהן he can’t marry this lady because he knows that he isn’t the one who was מאנס her in which case without him its really 50 כשרים and 50 פּסולים so there is no רוב! In other words, רע"א holds that if you aren’t part of the ספק then you don’t count as part of the רוב. The רש"ש disagrees with this רע"א and says that when it comes to הולכין אחר הרוב (as opposed to ביטול ברוב) even people who aren’t part of the ספק count towards the רוב.
2. The גמרא asks how we know that the דין of כל קבוע כמחצה ומחצה דמי is even said לקולא—perhaps it is only לחומרא? The גמרא responds that this is why we need the פּסוק of וארב לו to teach us that it even applies לקולא. The שערי יושר in שער ד׳ פּרק א ד"ה ועפּי"ד asks what the הוה אמינא was that כל קבוע would only apply לחומרא? He explains that if there is an איסור קבוע then that is a status that has a lot strength. However, היתר is not a real status—it is just the absence of איסור. Therefore, you might have thought that it is not חשוב enough. Therefore the פּסוק of וארב לו teaches us that just like someone who kills by accident is פּטור ממיתה even though not killing him is also just the absence of חיוב מיתה, so too by היתר.
3. The רמ"א in הלכות חנוכה in סימן תרע"ג סעיף א brings from the תרומת הדשן that if you mix up your חנוכה candles with other candles then it isn’t בטל because candles are a דבר שבמנין during חנוכה which are not בטל. The ט"ז in ס"ק ס"ק ו disagrees with the רמ"א’s reasoning but agrees that it isn’t בטל if the חנוכה candles didn’t move and the other candles got mixed in with it since כל קבוע כמחצה על מחצה דמי. The פּרי מגדים there says that this is incorrect since the rule of כל קבוע כמחצה על מחצה is only said where the אסור object is ניכר בפני עצמו. However, if all the candles look the same and got mixed up then we would say it is בטל חד בתרי.
4. The גמרא quotes a ברייתא that says that if you find a child in the street, if it is רוב גוים then you assume the child is a goy and if רוב ישראל then you assume he’s a Jew. The גמרא explains that this refers to the חיוב להחיותו. תוספות in ד"ה אם רוב says that if it is exactly 50/50 then you aren’t required to support the child. However, the רמב"ם in הלכות איסורי ביאה פּרק ט"ו הל׳ כ"ו says that in a case of exactly 50/50 there is a חיוב להחיותו. The קובץ שיעורים here explains the מחלוקת between תוספות and the רמב"ם as follows: תוספות understands that this is primarily a ספק ממון. Therefore, you can’t force someone to pay מספק because המוציא מחברו עליו הראיה. However, theרמב"ם views it primarily as a ספק מצוה and you therefore need to give the צדקה מספק since it is a ספק דאורייתא. רב אלחנן ז"ל questions both sides: if you hold like תוספות that it is primarily a ספקא דממונא, then even if it were רוב ישראל you should be פּטור since we have a principle of אין הולכין בממון אחר הרוב. If you hold like theרמב"ם that it is primarily a ספק מצוה then why would this be any different than a ספק מתנות כהונה which you are not obligated to give? He suggests that perhaps you (the owner) are fully מוחזק in the מתנות כהונה until you give it, as opposed to the מתתנות עניים which comes from a communal pot so there isn’t the classic מוחזק. However, he isn’t really happy with this תירוץ and leaves it צ"ע. The חתם סופר in משנת תקע"ג explains theרמב"ם’s שיטה differently. He explains that the child himself is obligated to keep the מצוות since he is a ספק דאורייתא. Therefore, even if כלפּי שמיא גליא he isn’t actually Jewish he isn’t worse than a גר תושב where there is a חיוב להחיותו.
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