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Safek Derabbanan Lkula
- There is a discussion if safek derabbanan lkula allows doing something initially or only after the fact. Some rishonim hold it is only permitted after the fact. However, others hold that safek derabbanan is permitted even initially.
- Some say that everyone agrees that safek isur derabbanan lkula is permitted even initially, but only a safek mitzvah derabbanan lkula is to be avoided initially.
- There is a dispute if safek derabbanan lkula applies to an area of halacha that is primarily deoritta even if this application is derabbanan.
Safek Derabbanan Lkula Bchezkat Isur
- The Shach holds that when there is a chazaka of an isur we're strict about a safek derabbanan, while the Pri Chadash disagrees. Gilyon Hashas Brachot 12a explains that the Ri holds like the Shach. Rashba Niddah 61b s.v. ha clearly seems to side with the Pri Chadash who is lenient. See further in Yabia Omer YD 8:5 and Taharat Habayit v. 3 p. 11. Sidrei Tahara end of 199 cites Taz in Hilchot Chatzitza who is lenient. Rash Mikavot 2:2 implies that he's lenient. Shaar Hamelech Mikvaot 10:7 writes that the dispute in the Tosfot Pesachim 9a centers around whether you can have a safek derabbanan lkula if there was a chazaka of it being asur. How do we pasken on those answers? (See Gra YD 331:84 who says we’re lenient but Derech Emunah Maaser 3:63 disagrees.) Shach (YD 110:21 and Nekudat Hakesef 69:5) is strict. Pri Chadash 110:34 and Taz 198:21 are lenient. Sidrei Tahara 199:40 and Taharat Habayit (v. 3, pp. 85-6) discuss this at length. Taz YD 69:24 is lenient and the Shaar Hamelech Mikvaot 10:6:7 disagrees. Meor Yisrael Pesachim 9a answers locally for the Taz but also that we’re lenient on every safek derabbanan where there’s a chezkat isur. Chida in Machzik Bracha 69:14 agrees with Pri Chadash. Meor Yisrael Pesachim 4a s.v. hamaskir (1) brings a proof for the Pri Chadash from Rosh Pesachim 1:2.
- Shach YD 201:148 contradicts himself and holds that safek derabbanan lkula is permitted even where there's a chezkat isur. Chazon Ish (Mikvaot 10:2) notes this contradiction.
- If there was a piece of something rabbinically forbidden that was recognizable in its own place before it fell into a mixture then it isn't considered itchazek isura and we're lenient to apply safek derabbanan lkula. If the pieces weren't recognizable when they fell into a mixture then it is considered itchazek isur and according to the Shach we don't apply safek derabbanan lkula.
Safek Derabbanan Lkula where you can be lenient either way
- If there's a safek derabbanan for two items and it is possible to be lenient either way but it is impossible logically to be lenient on both, then the halacha is that both are forbidden.
- For example, if 3 lugin of sheuvim water fell into one of two mikvaot that are incomplete both are invalid since there's no reason to assume it fell into one of them more than the other one. After the fact, if someone used one of these two mikvaot it is effective after the fact. Some disagree.
- For example, if something asur midrabbanan fell into one of two pots and it is unknown which it fell into, both are forbidden.
Safek Derabbanan Lkula when one didn't do anything
- Mishna Lmelech writes that safek derabbanan lkula only applies if he did something to permit the rabbinic prohibition. However, if he did nothing (dvar hamatiro) and there just is a safek, it is forbidden. However, Shaar Hamelech argues. Here are his proofs:
- Gemara Brachot 21a states that if Shema is only derabbanan and there's a safek if someone said Shema he doesn't need to repeat it. That indicates that safek derabbanan lkula is applied even though it is possible that no action was taken. However, it is possible to answer for Mishna Lmelech that a rabbinic mitzvah is more lenient and this type of safek is sufficient.
- Taz YD 69:24 writes that if someone doesn't remember if they salted a piece of meat before cooking it, it is permitted based on safek derabbanan lkula. Knesset Hagedola (Hagahot Bet Yosef 69:31) agrees. This implies that even though it is possible that no action was taken safek derabbanan lkula applies.
- Gemara Pesachim 9a is clear that fruit which were untithed in the possession of a religious person who passed away and it isn't clear if the owner tithed them before he passed away are permitted. This is an application of safek derabbanan lkula even though it is possible that nothing was done to permit the prohibition. See Shaar Hamelech how he deflects this proof.
- Ran and Rashba (Chullin Elu Terefot) write that food which is muchzak to be infested with bugs is forbidden even if it is cooked and perhaps the bugs dissolved. Seemingly, that indicates that safek derabbanan lkula does not apply if nothing was done to permit the prohibition. However, this can be because of the reason that safek cannot change a vaday or safek derabbanan does not apply if there's a chezkat isur.
- Mishna Mikvaot 2:2 establishes that according to Tana Kama safek derabbanan lkula applies to a person who is tameh midrabbanan even if there's a question he went to mikveh. Seemingly, this proves that safek derabbanan lkula applies even if it is unknown if anything was done to permit the prohibition. Mishna Lmelech answers that the case must be where the person who is tameh went to dip in the mikveh and there's a question if he dipped his body in the mikveh completely or if there was a chatzitza. This discussion is quoted by Pitchei Teshuva 201:44.
- Tur OC 394:1 holds that if there's a safek if he left the eruv he may not rely on it for carrying in the chetzer. This is Mishna Lmelech's proof to his thesis. Shaar Hamelech argues that the reason for this is there's two safekot why this would be forbidden: maybe he didn't place the eruv and maybe the eruv didn't last until ben hashemashot. If there's a safek safeka against a safek derabbanan Tur might hold that this is forbidden.
Safek Safeka - Safek Echad Bguf Safek Echad Btarovet
- If there is a safek safeka that is built of one safek about the status of the item in question and one safek since it was lost in a mixture, many rishonim consider this an invalid safek safeka. Others consider an acceptable safek safeka. One example is a safek teref piece of meat that was mixed up with other pieces of kosher meat (when bitul wasn't relevant). The halacha holds that it is an invalid safek safeka.
- If it is a safek safeka with one safek that is about the status of the item potentially a dvar sheyesh lo matirin and one safek of the tarovet it is an invalid safek safeka.
Safek Safeka MShem Echad
Safek Safeka With Kulot that are Soter One Another
- LChumra: Tosfot Niddah 27a and Bava Kama 11 are machmir. Pri Megadim Klalei Safek Safeka Hamechudashim n. 1 codifies this.
- Derabbanan’s: Ginat Veradim of pri megadim klal 2 says that the whole din of two sefakot that are soter one another might only apply to a deoritta safek safeka but not safek derabbanan lkula. It is like a taz and against a darkei moshe. Rabbi Akiva Eiger 49 is machmir.
- Maharshal on niddah 27a asks on tosfot so what there’s two kulot that are soter each other why can’t you be meikel on either you choose, why machmir on both. It is like kesil bchoshesh holech. Rav Ovadia in Taharat habayit v1 p276 quotes this and adds that the binyan tzion 1:60 and torat shlamim 187:29 agree. Rav Ovadia is machmir in end. (Maharsha there answers for tosfot. Aruch Lner niddah 27a says that from the proofs of tosfot it is mutually exclusive to prove kulot which are tartei dsatrei lchumra and also hold safek safeka doesn't work bchezkat isur (shach klalim 29). Therefore, acc to pri chadash we could accept tosfot but not acc to shach.)
- Rabbi Akiva Eiger in Beitzah 14a writes that the peshat in Tosfot is not that something for which you have a safek which would lead to a kula in opposite cases is asur. He says that’s wrong and against Shabbat 34b that for ben hashemashot we say we’re lenient for derabbanan’s like establishing an eruv even if for one person it is valid because he only set it up in middle of ben hashemashot and the other person’s had a dog eat his in middle. Same is true of one person over multiple shabbaton. Rather that peshat is wrong. Peshat in tosfot is dvar sheyesh lo matirin. He said he had an argument with the baal bet meir about this and this is how the bet meir concluded. (He’s assuming it is a dvar sheyesh lo matirin because you could grind it with a shinuy, that’s like the rif and not trumat hadeshen; also it is against pri chadash that dvar sheyesh lo matirin doesn’t apply to machloket haposkim; also it is against nodeh beyehuda’s idea of dvar sheyesh lo matirin by moving muktzeh).
- Rabbi Akiva Eiger (Drush V'chiddush Eruvin Maarechet 4) asks why safek eruv is kosher (Eruvin 35, Shulchan Aruch O.C. 409:6 and 415:2), but yet if he made two eruvin in two opposite directions which halacha doesn't allow for, he is stuck since he can't pick one to be valid (Eruvin 50, Shulchan Aruch O.C. 412:1). He (s.v. v'nireh li d'lechora) answers based on Tosfot Beitzah 14a that since either option would cause a different leniency he can't be lenient about either one. That's why when he made an eruv in both directions it doesn't work since he can't have both contradictory leniencies. However, if he wants just one eruv and it is a safek if it is valid, it is valid since that is only one leniency. Even though in that case he would have alternative techum which has other leniencies, since he wants his eruv to be valid it is considered as having only one leniency.
- Raavad in the Katuv Sham in Beitzah 14a says that anyone who listens to the pesak of tosfot to be machmir on both cases of spices is a kesil bchoshech holech. The Baal Hameor agreed with Tosfot.
- Korban Netanel moed katan 2:80 points out that the rosh and rif m”k are meikel on a mochleket amoraim for chol hamoed in both directions even though rosh beitzah agreed with tosfot. He said that tosfot beitzah 14a was only machmir because it was a safek cheshron yediya of which amora was the rav and which talmid so it was barur the din but we don’t know what it was.
- Raavad in Baalei Hanefesh (cited by rosh niddah 9:2 and s”a YD 184:4) writes that originally he was machmir for a veset safek by day and safek by night on both. Then he concluded to be lenient and only asur the daytime one. The Baal Hameor in the end is lenient as well. S”A follows the raavad. Chatom sofer on s”a says that s”a is wrong because of other opinion in raavad said tartei dsatrei kulot here so why be lenient you have to be machmir on both. He compares it to a case of being toleh a ketem with two woman (niddah 60a) which we’re machmir on because of chucha vtelula. Rest of poskim follow s”a. Haflah on yd 184:4 says in theory chatom sofer’s right from Tosfot Beitzah 14a but the raavad came up with a hachraah why the second was more chamur.
- Pri Megadim E”A 538:2 cites from mishna lmelech megillah based on Ran Pesachim 108a that if it isn’t oker takana completely it is muter to be lenient in both directions. Gra on s”a 538 says s”a is stirah to s”a 504 by yom tov. Tzarich iyun.
- Rabbi Akiva Eiger megillah 5b s.v. nitkashti seems to be assuming unlike tosfot bk 11 as he’s trying to explain why the gemara ask on rebbe who did melacha maybe it was because of safek derabbanan. There he backs down because of pri chadash that safek dvar shyesh lo matirin doesn’t apply to a machloket haposkim. See R’ Yitzchak Yosef’s article on tartei dsatrei bderabbanan in Ayin Yitzchak Shulchan Marechet p.55 who quotes his father’s answer (Chazon Ovadia 1:13:198) to this R’ Akiva Eiger based on tosfot bk 11 and nidah 27 and the yerushalmi megilah.
- With respect to tefillah see tosfot brachot 2a and kehilat yakov that avid kmar is unique because of elu velu.
Safek Safeka - Safek Eched Deoritta Safek Eched Derabbanan
- Rashba Brachot 31a cites a dispute regarding something which is a biblically forbidden but there’s a doubt if it is forbidden and additionally another reason why it might not be a biblical prohibition but would be a rabbinic one. Do we say safek safeka in such a case?
- The Gemara Pesachim 9a implies that a case where there’s a doubt if it was checked for chametz and additionally there’s a doubt if bitul chametz occurred it must be checked again. That seems to prove that it isn’t a safek safeka and is forbidden. The Rashba answers that chametz might be more serious than other prohibitions. The Tosfot HaRash Pesachim 9a answers that the case was where there was no bitul. They’re both assuming that we would apply safek safeka in such a case.
- Do we follow that answer of the Rashba or Rash? Locally in Brachot 31a this question which the Rashba was discussing affects a case of food brought into the house unprocessed whether it is exempt from trumah altogether. The Gra YD 331:84 writes that we follow the strict opinion in that discussion and accordingly we’d be lenient to consider it a safek safeka. Rav Chaim Kanievsky in Derech Emunah Maaser 3:63 holds that the Rambam is lenient and if so we’d be strict about the safek safeka.
- Shach Klalei Safek Safeka YD 110:16 writes that is a safek safeka. A proof for this can be found in Rama YD 122:9 and Shach 122:8.
- Application: Rabbi Akiva Eiger OC 184 says it about if a woman isn't sure if she said birkat hamazon that she doesn't have to repeat it.
- How it works: The Teshuva Mahava 234 explains that seemingly it is a safek that isn't mithapech since one safek is whether it is biblical or rabbinic. Either way according to that safek it is forbidden. He explains that on a biblical level it is a safek safeka that is mithapech.
Chazaka - Tzarich Levarer
- Something which is permitted based on the principle of chazaka should be checked to verify that it is nonetheless still the case. Some say that this is only necessary when there is a previous status of a forbidden chazaka.
Safek Safeka - Tzarich Levarer
- Some hold that anything which is permitted with a safek safeka and can be verified with further investigation must have that done. Others disagree. The Shach concludes that if clarifying the safek safeka would involve a large loss of money one doesn't have to investigate it.
- For example, if someone cooked in a pot and the only way to permit the food would be if the pot wasn't used within 24 hours some hold that one should investigate when it was last used and others hold it isn't necessary.
Safek Safeka with Chezkat Isur
Safek Safeka Lheter against a Safek Safeka Lisur
- If there are three safekot to permit something and only two to forbid it it is still considered a safek safeka and it is permitted.
- Many achronim are lenient on kavuah of a rabbinic prohibition.
Rov of Poskim
- If poskim didn't argue face to face we don't consider them to be a majority that is effective in conclusively deciding a halacha.
Rov Efsher Levarer
- Anytime that we rely upon majority and the actual facts can be investigated one must do so. For example, even though majority of animals are kosher we nonetheless check the lungs of an animal to verify that indeed it is kosher.
Safek Deoritta Lchumra
- Reem on Samag Megillah writes that the principle of Safek Derabbanan is only permitted after the fact. Ran Menachot 65a agrees. Rav Ovadia in Chazon Ovadia v. 1 p. 201 supports this from the position of the Ran, Maharam Chalavah, and Raavad that when it is easy we should be strict for a safek derabbanan.
- Ramban (Yevamot 24a), Rashba (responsa 4:48), Rambam (Responsa Blau siman 308, 310). Ramban is quoted by Otzar Haposkim EH 6:1:8. Pri Chadash (Klalei Safek Safeka 110:4) holds that safek derabbanan is permitted even initially. Rav Ovadia cites many who agree including the Get Mekushar 147c and Divrei Emet 9:4.
- Rav Ovadia citing the Mutzal M'esh 13 based on Menachot 68b, Michtam LDovid 17 s.v. amnam
- Rashba Eruvin 11a s.v. may is strict on a doubt regarding walls for an eruv even in a case that it is derabbanan since there's another 3 walls, because in general the halacha of having walls for an eruv is deoritta. He cites two sources for this and expands this to a general concept that we're strict anywhere that the primary discussion is deoritta.
- Klalei Safek 110:21, Shach 111:4
- Shach 111:4, Pri Megadim S"D 110:38
- Mishna Mikvaot 2:3, Rambam Mikvaot 10:2, Shulchan Aruch Y.D. 201:68, Shach 201:142
- Shach 201:148
- Chazon Ish Mikvaot Tinyana 10:2
- Shulchan Aruch Y.D. 111:6
- Hilchot Bechorot 4:1
- Mikvaot (10:6:1 and 7 at the end)
- The Reem on Smag Megillah writes that safek safeka is only permitted after the fact. See Rosh Bechorot 9a
- Rav Ovadia in Chazon Ovadia 1:202 citing Perach Shoshan EH 3:2, Kol Eliyahu YD 2:2, Rosh A"Z 2:35
- Tosfot Beitzah 3b s.v. vacherot writes that Rabbenu Tam considers a safek safeka even if one safek is about the status of an item and one safek is about a tarovet. This is also the opinion of Tosfot Zevachim 71a and Riva in Shitah Mikubeset Zevachim 74a. However, the Ri cited by Tosfot disagrees that such a safek safeka is an invalid safek safeka. Rashba Beitzah 3a s.v. nitarva explains the opinion of the Ri; since the first safek is about the status of an item we determine that we are strict since it is a safek deoritta lchumra. Then we consider the second safek however at that time there's only one other safek. Rashba responsa 401 agrees with Rabbenu Tam.
- Shulchan Aruch YD 110:9 holds it is an invalid safek safeka. Gra 110:10 writes that most poskim assume that it is an invalid safek safeka.
- Shulchan Aruch 102:1. Shach 102:2 writes that everyone agrees for dvar sheyesh lo matirin one safek in the guf and one in the tarovet is forbidden.
- Tosfot Ketubot 9a
- Shach Klalei Safek Safeka n. 12. His proof is Tosfot Avoda Zara 38b with regards to Stam Kli Eino Ben Yomo.
- The Rashba Chullin 10b establishes that when if something is permitted based on a previous status which established a chazaka if it can be verified it should be. For example, if a shochet's knife was previously knife it should nonetheless be checked before being used.
- The Shulchan Aruch O.C. 8:9 states that one should check his tzitzit before reciting a bracha upon it each morning even though there is a chazaka that it was kosher the previous day. Magen Avraham 8:11 compares this to YD 1 where it is necessary to check into the status of the shochet even though there's a majority that are experts. Dagul Mirvava (on Magen Avraham 8:11) notes that the Magen Avraham seems to be in contradiction his ruling in Magen Avraham 437:4 that it is only necessary to further investigate if there was a chazaka of something prohibited. Nodeh Beyehuda OC 2:1 also notes this contradiction. In Hilchot Niddah, Dagul Mirvava on Shach YD 187:19 proves that this is also the position of the Shach. Generally, the Magen Avraham and Shach's position is also that of the Bet Yosef OC 437:2 as the Magen Avraham notes. However, Chatom Sofer answers the Nodeh Beyehuda's question by saying that a chazaka does need verification always, whereas a rov doesn't unless it is going against a chazaka of something previously prohibited. Even though a majority is greater than a previous chazaka it is only slightly better and still needs to be verified. When there is no previous chazaka of something prohibited the majority doesn't need any verification. However, a chazaka is intrinsically weaker and as long as there's some concern something could have changed it always needs to be verified. Even Haazel (Chametz Umatza 2:17) agrees. The Bach 437:2 argues with the Bet Yosef and differentiates between whether the permitted status is established with an action or a natural phenomenon. If it is based on an action then it needs to be verified since it is subject to error, however, if it is a naturally occurring process it doesn't need to be verified. See Meor Yisrael Pesachim 4a s.v. lmay who compares the argument of the Bach to Bechorot 20a. See Yabia Omer EH 7:1:2.
- An alternate approach is taken by the Gra (on OC 8:9). He addresses the issue by stating it depends on whether there is a miyut hamatzuy. In the case of Pesachim 4a there is a miyut hamatzuy of people who don't do bedikat chametz and as such it needs verification. The same is true of checking whether the shochet was an expert or whether the tzitzit strings broke. However, the other terefot besides the lungs don't need to be verified since there isn't a miyut hamatzuy of terefot. Chatom Sofer (on Magen Avraham 437:4) agrees. This is almost explicitly also the approach of the Ran Chullin 3b s.v. vheycha. See further the Ritva Pesachim 4a.
- See also Avnei Nezer YD 1 for a novel explanation as to why the Gemara Pesachim 4a uniquely requires verification. Finally, note that the Rambam Chametz Umatzah 2:17 entirely omits the Gemara Pesachim 4a's requirement for verification. Pri Megadim E"A 437:4 supposes that the Rambam held like the Bach 437:2's reading of the gemara that it is never necessary to verify something established with a majority.
- Ran (Respona 66) writes that it is a good thing to check the mikveh that it has 40 seah before using it even though the chazaka is that it is kosher and it isn't known to change over time. Ran compares this with checking the house if it had bedikat chametz. This clearly indicates that it is necessary to check something established by a chazaka. Shulchan Aruch YD 201:65 codifies this. This seems to be against Bet Yosef and Magen Avraham 437 but can be explained by Chatom Sofer that something with a chezkat heter needs a birur. Gra 201:115 follows his position to explain that it is only necessary to check if there's a miyut hamatzuy of there being an issue.
- Rama Y.D. 110:9 writes that one does not need to investigate anything that is permitted with a safek safeka because it is completely permitted. Shach YD 110:66 disagrees based on the Rashba. Rashba Chullin 53b s.v. ki pligi writes that whenever one can investigate a safek safeka further one must do so. He compares it to something in a mixture which is recognizable not being nullified and extends it to where it is possible to verify the facts that one should do so. Shach then shows from the Smag, Sefer Hatrumah, and Mordechai that we can be lenient and not require checking into a safek safeka. Finally he makes a compromise to requrie checking when possible and wouldn't cause a large loss of money. Pri Chadash (Klalei Safek Safeka n. 2) disagrees and hold that it isn't necessary and proves it from the Rashba in two other places and answers the Shach's proofs. Chavot Daat (Klalei Safek Safeka 35) disagrees with the Shach's proofs but concludes (Safek Safeka Bkatzara 35) that he agrees with the Shach. In one of his arguments he says that it isn't necessary to investigate a safek safeka if you can't investigate both of the sefakot. For that proposition he also cites that the Nodeh Beyehuda YD 43 s.v. omer, 57 s.v. heneh agrees. Yabia Omer YD 5:3:2 concludes like the Pri Chadash and Shaar Hamelech that it isn't necessary to verify once there is a safek safeka. He also adds that asking someone something that they might be embarrassed answering isn't necessary.
- Yabia Omer YD 5:3:2. He cites the Beer Sheva 30 who writes that it is necessary to figure out whether a pot was used within 24 hours and one can't just rely upon the principle that most utensils weren't used within 24 hours. His proof is Pesachim 4a. Yabia Omer disagrees based on the Pri Chadash (Safek Safeka n. 2) in his disagreement with the Shach that it isn't necessary to investigate a safek safeka and stam kelim einan bnei yoman is based on a safek safeka (Tosfot Avoda Zara 38b). To this end he cites the Radvaz 4:296 and Kneset Hagedola Hagahot Hatur 122:13 who agree with him.
- Shach 110:27, Taz 110:15
- Rama 110:9, Pri Chadash safek safeka 16. See Rashba teshuva 401
- Shach 110:28
- Rama 96:4 since it might not be cut with a non-kosher knife and the food might not be charif and the knife was eino ben yomo. The knife being eino ben yomo itself is a safek safeka.
- Pri Megadim S"D 110:38, Rav Poalim YD 1:28, Minchat Cohen Tarovet 3:5 cited by Pri Megadim. Pri Megadim Mishmeret Shalom fnt. 152 cites that the Pri Chadash 339:1, Aruch Hashulchan 110:10, and Kahal Yehuda 110:3 are lenient and Yad Yehuda 110:47 is strict. It also references Maharsham CM 46, Bet Yitzchak (Shaar Kavuah 7), Taz 673:6, Aruch Hashulchan 453:9, Rabbi Akiva Eiger 112:1, and Chikrei Lev YD 1:105.
- The Pri Megadim explains that if the prohibition was not identifiable before the question arose it is forbidden because of the principle that when there's two pieces and we can't choose which to permit using safek derabbanan lkula we're strict on both. That isn't relevant here since the pieces were identifiable that they are forbidden or permitted before the doubt arose and as such there's no principle that we're strict on both pieces (Shach Klalim n. 21, Shach 111:4).
- The Tosfot Pesachim 9b s.v. haynu tesha is a proof that for a rabbinic question we are lenient even though it is kavuah. The case is where there's a mouse who took a piece of either chametz or matza and the piece in question was taken from a place that was kavuah. Once he brought it into the house there's a question whether it is obligated in Bedikat Chametz which is rabbinic. Tosfsot thinks it is clear that we are lenient since it is only rabbinic. Tosfot Rosh and Tosfot Rabbenu Shimshon make this even more explicit. Baal Hameor has the same conclusion. The Raavad only disagrees for a local reason because of chametz. Rambam Chametz Umatza 2:10 and Rashi Pesachim 9b who seem to hold unlike Tosfot could similarly hold like the approach of the Raavad as the Maggid Mishna notes. Tur 439:1 and Pri Chadash 439:1 rule like Tosfot.
- Get Pashut by Maharam Ben Chaviv at the end Klal 1, Minchat Chinuch 78:2. See Yabia Omer 2:12:3 and other places where rov poskim is certainly used as a factor in pesak though not as a definitive rov.
- Ran (on Rif Pesachim 1b; on Gemara Pesachim 4a) writes that it is evident in the gemara that even if there is a majority of people who do bedikat chametz if someone rents a house and doesn't know whether the owner checked, he should verify with the owner if that is possible. He compares it to the ruling of the Rif Chullin 3b that if someone did a shechita and we don't know if he's an expert in the laws of shechita, even though a majority are experts we should verify that he knows the laws if that is possible. Maharam Chalavah Pesachim 4b s.v. may and Rabbenu Dovid Bonfid Pesachim 4a s.v. may agree. The Rashba Chullin 3a s.v. amar and 10b s.v. umiyhu accepts the Rif and proves it from the Gemara Chullin, though he does not connect it to the Gemara Pesachim. He gives 3 examples where we rely upon a rov and yet require verification when possible: we check that the shochet is an expert, we check the knife for shechita, and we check the lungs of an animal to make sure it is kosher even though a majority are kosher. He attributes this approach to his teacher, the Ramban, as well. The Ritva Chullin 3b s.v. mishum cites this approach of the Rif, yet the Raah disagreed. Whenever there is a majority there is no need to check or verify further. In Pesachim, Ritva 4b s.v. delayteh addresses the proof of the Ran and answers that in fact it depends on the percentage of the majority. When there is a certain higher threshold no verification is necessary, but below that it is. See Bet Yosef 437 and Magen Avraham 437:4 who accept this Ran and apply it further.
- Rambam (Responsa Blau, siman 310). Rav Shlomo Ginzler (Yeshrun p. 34) quotes the fuller text of that teshuva with the line that makes it clear that safek deoritta lchumra is only derabbanan is learned from mamzer vaday v'lo mamzer safek.
- Taz 201:85 indicates that Ran holds that a mikveh which is not known to leak is kosher if it was known to have 40 seah and currently has 40 seah. Even though it is unknown that there were 40 seah when someone used it in between that is fine since there's no suspicion that it became invalidated. This implies that if it wasn't known to begin with that it had 40 seah it would be an issue. However, Rash Mikvaot 2:1 implies this is permitted. Taz adds that it is possible that even Ran agrees that it is permitted.