Eruvin 36a:16

רָבָא אָמַר: הָתָם תְּרֵי חֶזְקֵי לְקוּלָּא, וְהָכָא חֲדָא חֲזָקָה לְקוּלָּא. Rava said: That is not the way to resolve the apparent contradiction between the two rulings; rather, there is a difference between the cases with regard to the ritual impurity itself: There, with regard to touching a person who was later found dead, there are two presumptions supporting leniency, whereas here, with respect to the teruma being used for an eiruv, there is only one presumption supporting leniency. How so? With regard to one who touched another person who was later found to be dead, there are two presumptions of purity: Firstly, the person who was found dead was previously alive, and the presumption is that he remained in that state until we know with certainty that he was dead. Secondly, the one who touched that person was previously pure, and he remains in that presumptive state until we know with certainty that he became impure. Therefore, Rabbi Meir had adequate reason to be lenient. However, with regard to teruma, only one presumption exists, that the teruma was previously pure and presumably remained in that state until proven otherwise. Since there is no additional presumption, Rabbi Meir ruled stringently.

קַשְׁיָא דְּרַבִּי יוֹסֵי אַדְּרַבִּי יוֹסֵי! All the difficulties raised above are based on the seemingly conflicting statements of Rabbi Meir. Yet it would appear that there is also a contradiction between one statement of Rabbi Yosei and another statement of Rabbi Yosei, for he was stringent with regard to the doubts involving ritual baths but lenient with regard to doubts involving eiruv.

אָמַר רַב הוּנָא בַּר חִינָּנָא: שָׁאנֵי טוּמְאָה, הוֹאִיל וְיֵשׁ לָהּ עִיקָּר מִן הַתּוֹרָה. שַׁבָּת נָמֵי דְּאוֹרָיְיתָא הִיא? קָסָבַר רַבִּי יוֹסֵי: תְּחוּמִין דְּרַבָּנַן. Rav Huna bar Ḥinnana said: The law with regard to ritual impurity is different, since it has a basis in the Torah. Therefore, Rabbi Yosei was stringent even with respect to immersion performed in order to remove impurity that is only of rabbinic origin. The Gemara asks: The prohibitions of Shabbat limits are also prohibited by Torah law; why isn’t Rabbi Yosei stringent about them as well? The Gemara answers: Rabbi Yosei holds: The laws of Shabbat limits are by rabbinic law, not by Torah law.

וְאִיבָּעֵית אֵימָא: הָא דִּידֵיהּ, הָא דְּרַבֵּיהּ. דַּיְקָא נָמֵי, דְּקָתָנֵי: אָמַר רַבִּי יוֹסֵי: אַבְטוּלְמוֹס הֵעִיד מִשּׁוּם חֲמִשָּׁה זְקֵנִים שֶׁסְּפֵק עֵירוּב כָּשֵׁר — שְׁמַע מִינַּהּ. And if you wish, say instead: This stringent ruling is his; that lenient ruling with regard to an eiruv is his teacher’s. The Gemara comments: The language of the mishna is also precise according to this explanation, as we learned in the mishna that Rabbi Yosei said: The Sage Avtolemos testified in the name of five Elders that an eiruv whose validity is in doubt is valid. This formulation indicates that Rabbi Yosei was merely reporting a ruling that he had heard from his teacher, although he may not have accepted it. The Gemara concludes: Indeed, conclude from this that this resolution of the contradiction is correct.

רָבָא אָמַר, הָתָם הַיְינוּ טַעְמָא דְּרַבִּי יוֹסֵי: הַעֲמֵד טָמֵא עַל חֶזְקָתוֹ, וְאֵימָא לֹא טָבַל. Rava said that a different resolution of the contradiction may be suggested: There, with regard to ritual baths, this is the reason for Rabbi Yosei’s opinion: Keep the impure person in his presumptive state of ritual impurity, and say that he did not properly immerse himself.

אַדְּרַבָּה הַעֲמֵד מִקְוֶה עַל חֶזְקָתוֹ, וְאֵימָא לֹא חָסַר! בְּמִקְוֶה שֶׁלֹּא נִמְדַּד. The Gemara responds: On the contrary, keep the ritual bath in its presumptive state of validity and say that the ritual bath was not lacking the requisite measure of water. The Gemara answers: We are dealing here with a ritual bath that had not been previously measured to determine whether it contained forty se’a, and therefore it had no prior presumption of validity.

תַּנְיָא: כֵּיצַד אָמַר רַבִּי יוֹסֵי סְפֵק עֵירוּב כָּשֵׁר? עֵירַב בִּתְרוּמָה, סָפֵק מִבְּעוֹד יוֹם נִטְמֵאת סָפֵק מִשֶּׁחָשֵׁיכָה נִטְמֵאת; וְכֵן בְּפֵירוֹת, סָפֵק מִבְּעוֹד יוֹם נִתַּקְּנוּ סָפֵק מִשֶּׁחָשֵׁיכָה נִתַּקְּנוּ — זֶה הוּא סָפֵק עֵירוּב כָּשֵׁר. It was taught in the Tosefta: In what case did Rabbi Yosei say that an eiruv whose validity is in doubt is nevertheless valid? For example, if one established an eiruv with teruma that had been ritually pure but later became impure, and there is doubt whether it became impure while it was still day, before the onset of Shabbat, or whether it became impure only after nightfall, and similarly, if one made an eiruv with untithed produce that was later tithed and thereby became permissible for eating, and there is doubt whether it was rendered fit while it was still day, before the onset of Shabbat, or whether it was rendered fit only after nightfall, this is an eiruv whose validity is in doubt which Rabbi Yosei said is valid.

אֲבָל עֵירַב בִּתְרוּמָה, סָפֵק טְהוֹרָה סָפֵק טְמֵאָה; וְכֵן בְּפֵירוֹת, סָפֵק נִתַּקְּנוּ סָפֵק לֹא נִתַּקְּנוּ — אֵין זֶה סְפֵק עֵירוּב כָּשֵׁר. However, if one established an eiruv with teruma about which there was doubt whether it was ritually pure or ritually impure from the outset; and similarly, if one established an eiruv with produce about which there was doubt from the outset whether it had been tithed and thereby rendered fit or whether it had not been tithed and thereby rendered fit, this is not a case of an eiruv whose validity is in doubt that Rabbi Yosei said is valid.

מַאי שְׁנָא תְּרוּמָה — דְּאָמַר הַעֲמֵד תְּרוּמָה עַל חֶזְקָתָהּ, וְאֵימָא טְהוֹרָה הִיא; פֵּירוֹת נָמֵי — הַעֲמֵד טֶבֶל עַל חֶזְקָתוֹ, וְאֵימָא לֹא נִתַּקְּנוּ! The Gemara raises a question in order to clarify the Tosefta: What is different about teruma, with regard to which we say: Keep the teruma in its presumptive state of ritual purity, and say that it was still pure at the onset of Shabbat, since it had been previously pure and it is not known when it became impure? According to that reasoning, with regard to untithed produce [tevel] it should also be said: Keep the untithed produce in its presumptive state, as the produce had certainly been untithed originally, and say that it was not tithed and thereby rendered fit prior to the onset of Shabbat.

לָא תֵּימָא: סָפֵק מִבְּעוֹד יוֹם נִתַּקְּנוּ, אֶלָּא אֵימָא: סָפֵק מִבְּעוֹד יוֹם נִדְמְעוּ, סָפֵק מִשֶּׁחָשֵׁיכָה נִדְמְעוּ. Rather, emend the wording of the Tosefta: Do not say: There is doubt whether it was rendered fit while it was still day, before the onset of Shabbat. Rather, say: There is doubt whether regular produce became mixed with untithed produce while it was still day, or whether it became mixed only after nightfall. In other words, one used regular food to establish his eiruv, but then tevel was mixed with that food, prohibiting the entire mixture from being consumed until tithes are separated for the tevel. However, there is doubt whether the produce became mixed with the tevel while it was still day, in which case the eiruv is invalid, or whether it became mixed only after nightfall, in which case the eiruv is valid. In that case, we say: Keep the produce in its presumptive state and say that it was not mixed with tevel during the day, and therefore the eiruv is valid.

בְּעָא רַב שְׁמוּאֵל בַּר רַב יִצְחָק מֵרַב הוּנָא: הָיוּ לְפָנָיו שְׁתֵּי כִכָּרוֹת, אַחַת טְמֵאָה וְאַחַת טְהוֹרָה, וְאָמַר: עָירְבוּ לִי בַּטְּהוֹרָה בְּכׇל מָקוֹם שֶׁהִיא, מַהוּ? Rav Shmuel bar Rav Yitzḥak raised a dilemma to Rav Huna: If there were two loaves of teruma before someone, one that was ritually impure and one that was ritually pure, and he did not know which one was pure; and he said: Establish an eiruv teḥumin for me with the pure loaf, wherever it is, i.e., even though I do not know which it is, I wish to establish my Shabbat residence at the location of the pure loaf, and those present placed both loaves in the same place, what is the halakha? Is this a valid eiruv or not?

תִּיבְּעֵי לְרַבִּי מֵאִיר, תִּיבְּעֵי לְרַבִּי יוֹסֵי. תִּיבְּעֵי לְרַבִּי מֵאִיר: עַד כָּאן לָא קָאָמַר רַבִּי מֵאִיר הָתָם — דְּלֵיכָּא טְהוֹרָה. הָכָא — הָא אִיכָּא טְהוֹרָה. אוֹ דִילְמָא: אֲפִילּוּ לְרַבִּי יוֹסֵי, לָא קָאָמַר אֶלָּא הָתָם, דְּאִם אִיתָא דְּהִיא טְהוֹרָה — יָדַע לַהּ. אֲבָל הָכָא, הָא לָא יָדַע לַהּ? The Gemara clarifies: The question may be asked according to the stringent opinion of Rabbi Meir, and it may be asked according to the lenient opinion of Rabbi Yosei. The question may be asked according to the opinion of Rabbi Meir in the following manner: Perhaps Rabbi Meir only stated his stringent opinion with regard to a questionable eiruv there, where there is no teruma that is definitely pure present, but only teruma whose purity is in doubt. Here, however, there definitely is a pure loaf, and therefore even Rabbi Meir may agree to rule leniently. Or perhaps it may be argued that even according to the opinion of Rabbi Yosei, he only said that we are lenient with regard to an eiruv whose validity is in doubt in the case dealt with there, where, if indeed the teruma is pure, he knows where it is; but here, he does not know how to identify it.

אֲמַר לֵיהּ: בֵּין לְרַבִּי יוֹסֵי בֵּין לְרַבִּי מֵאִיר בָּעִינַן סְעוּדָה הָרְאוּיָה מִבְּעוֹד יוֹם — וְלֵיכָּא. Rav Huna said to Rav Shmuel bar Rav Yitzḥak: According to both the opinion of Rabbi Yosei and the opinion of Rabbi Meir, we require that an eiruv consist of a meal that is fit to be eaten while it is still day, prior to the onset of Shabbat, and in this case there is none. Due to the uncertainty as to which loaf is pure and which is impure, neither of the two loaves may be eaten, and an eiruv made with food that may not be eaten while it is still day is not a valid eiruv.

בְּעָא מִינֵּיהּ רָבָא מֵרַב נַחְמָן: כִּכָּר זוֹ הַיּוֹם חוֹל וּלְמָחָר קֹדֶשׁ, וְאָמַר: עָירְבוּ לִי בָּזֶה, מַהוּ? אֲמַר לֵיהּ: עֵירוּבוֹ עֵירוּב. Rava raised another dilemma to Rav Naḥman: If one said: This loaf shall remain unconsecrated today, and tomorrow it shall be consecrated, and he then said: Establish an eiruv for me with this loaf, what is the halakha? Do we say that since the twilight period’s status as part of the previous day or part of the day that follows is questionable, the consecration of the loaf may take effect before the eiruv establishes one’s Shabbat residence, and since an eiruv cannot be made with a consecrated object, the eiruv is not valid? Rav Naḥman said to Rava: In that case, his eiruv is a valid eiruv.

הַיּוֹם קֹדֶשׁ וּלְמָחָר חוֹל, וְאָמַר: עָירְבוּ לִי בָּזֶה, מַהוּ? אֲמַר לֵיהּ: אֵין עֵירוּבוֹ עֵירוּב. מַאי שְׁנָא? Rava then asked about one who made the opposite statement: This loaf shall be consecrated today, and tomorrow it shall be unconsecrated, i.e., it shall be redeemed with money that I have in my house, and he then said: Establish an eiruv for me with this loaf, what is the halakha? Rav Naḥman said to him: His eiruv is not a valid eiruv. Rava asked him: What is different between the two cases? If we are lenient with regard to the twilight period, we should be lenient in both cases.

תְּנַן הָתָם: לָגִין טְבוּל יוֹם שֶׁמִּלְּאוֹ מִן הֶחָבִית שֶׁל מַעֲשֵׂר טֶבֶל, וְאָמַר: הֲרֵי זֶה תְּרוּמַת מַעֲשֵׂר לִכְשֶׁתֶּחֱשַׁךְ — דְּבָרָיו קַיָּימִין. We learned in a mishna there: If one filled a flask that was immersed during the day [tevul yom] but does not become fully ritually pure until night from a barrel of tithe that was still tevel, meaning that the produce inside was first tithe from which teruma of the tithe had not yet been separated, and he said: Let the contents of this flask be teruma of the tithe for the contents of the barrel when night falls, his statement takes effect. If he were to say that the designated portion should immediately become teruma of the tithe, the teruma of the tithe would be defiled by the flask that is still a tevul yom. Once night falls, however, the flask is absolutely pure, and if the designation of the flask’s contents as teruma of the tithe takes effect at that time, the produce remains pure. The mishna teaches that teruma of the tithe can be separated in this manner.

וְאִם אָמַר: עָירְבוּ לִי בָּזֶה — לֹא אָמַר כְּלוּם. אָמַר רָבָא זֹאת אוֹמֶרֶת: סוֹף הַיּוֹם קוֹנֶה עֵירוּב, The mishna continues: And if he said: Establish an eiruv for me with the contents of this flask, he has not said anything, as the contents of the flask are still tevel. Rava said: That is to say that the end of the day is when the eiruv acquires one’s Shabbat residence. The critical time with respect to an eiruv is the last moment of Shabbat eve, rather than the first moment of Shabbat.