Resources for Yevamos daf 45
1. The גמרא says that if you hold עבד ועכו"ם הבא על בת שראל הולד כשר then the לימוד from אשת אב is that just as אשת אב has תפיסת קידושין with other people, so to in order to create ממזירות you need to have קידושין with other people. Consequently עכו"ם cannot create ממזירות. The רשב"א asks that it should be a ק"ו that an עכו"ם should create a ממזר? If someone never has תפיסת קידושין why would that make him less likely to create a ממזר? He answers as follows: if normally there is a תפיסת קידושין then we can assume if there is no תפיסת קידושין then it must be because of the איסור ערוה. However, if there is never a תפיסת קידושין then perhaps it isn’t because of ערוה and perhaps the child isn’t a ממזר. In the קובץ הערות in סימן ל"ה he explains this in terms of a חקירה: is the lack of תפיסת קידושין a “סיבה” which in and of itself is the cause for ממזירות, or is it just a "סימן" where the lack of תפיסת קידושין happens to be caused by the same issue that causes ממזירות which is ערוה but it is really the ערוה that is the cause for the lack of תפיסת קידושין. He explains that according to the רשב"א these are the two sides of the מחלוקת of how we learn from אשת אב. The one who holds the child from an עכו"ם is a ממזר holds no תפיסת קידושין is a סיבה. However, if you hold the ולד is כשר then it must be that no תפיסת קידושין is just a סימן and you don’t have that סימן if קידושין is anyway not valid by an עכו"ם. He then asks an interesting question from the famous גמרא in תמורה that discusses the concept of אי עביד לא מהני (if you do something against the תורה it doesn’t work): the גמרא asks that if אי עביד לא מהני were true then why if a כהן marries a גרושה is the קידושין valid? The גמרא answers that if the קידושין wasn’t חל, then the children would have to be ממזירם. However, we have a special דרשה that the children from that marriage aren’t ממזרים so it must be the קידושין was חל. רב אלחנן ז"ל asks that this only makes sense if you say that lack of תפיסת קידושין is a סיבה for ממזירות. However, if it is just a סימן there is ערוה then the issue here is אי עביד לא מהני and not ערוה so why do you need a פּסוק to say he isn’t a ממזר? He suggests that אי עביד לא מהני isn’t what makes it not חל but rather the איסור itself in which case it is ערוה here as well that stops the קידושין.
2. The גמרא says “מי לא טבלה לנידותה” which sounds like a person can become a גר when going to the מקוה for reasons other than גירות. תוספות in ד"ה מי asks a fundamental question: what about the requirement of having a ב"ד of three witness the טבילה? He answers that perhaps that is only necessary for קבלת המצוות but not for טבילה. The רמב"ן brings the בה"ג who says you don’t need three בזמן הזה but the רמב"ן rejects that opinion and answers similar to תוספות that as long as there was a קבלת מצוות in front of three (which includes the commitment to do מילה וטבילה ) then doing the טבילה in front of three is not מעכב the גירות. The רמב"ם in הלכות איסורי ביאה פּרק י"ג הל׳ ט seems to understand our גמרא completely differently. He learns that our גמרא is saying that if we see someone acting in accordance with Jewish law like going to the מקוה for נדה or קרי then we can assume that they did their original גירות correctly in front of a ב"ד. The אחיעזר in חלק ג סימן כ"ז points out that the according to theרמב"ם the גמרא is much easier to read since the גמרא says מי לא טבל לקרויו? טבילת קרי post the destruction of the בית המקדש is just a תקנת עזרא and can even be done with מים שאובין so how would seeing someone do that help them become a גר when מים שאובין is not valid for גרות? However, like the רמב"ם ‘s understanding there is no question since the טבילה is only an indicator that the גירות done in the past was valid. However, the רמב"ן disagrees with the רמב"ם because if the רמב"ם was correct then why mention טבילה at all? Why not say are they שומר שבת? He does not answer the question.
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