תַּנְיָא, רַבִּי אֱלִיעֶזֶר בֶּן תַּדַּאי אוֹמֵר: אֶחָד זֶה וְאֶחָד זֶה צְרִיכִין לְעָרֵב. וַאֲפִילּוּ לָזֶה בְּיַיִן וְלָזֶה בְּיַיִן?
It was taught in a baraita: Rabbi Eliezer ben Taddai says: In both this case, of wine and wine, and that case, of wine and oil, they must establish an eiruv. The Gemara expresses wonder: Did he say this even if the partnership is with this one in wine and also with the other one in wine? Why should these partnerships not be sufficient to consider the items merged?
אָמַר רַבָּה: זֶה בָּא בִּלְגִינוֹ וְשָׁפַךְ, וָזֶה בָּא בִּלְגִינוֹ וְשָׁפַךְ — כּוּלֵּי עָלְמָא לָא פְּלִיגִי דְּהָוֵי עֵירוּב.
Rabba said: If they partnered in the following manner, such that this one came with his wine-filled jug and poured its contents into a barrel, and the other one came with his jug and poured his wine into that same barrel, everyone agrees that it is a valid eiruv, even if they did not act specifically for that purpose.
כִּי פְּלִיגִי כְּגוֹן שֶׁלָּקְחוּ חָבִית שֶׁל יַיִן בְּשׁוּתָּפוּת, רַבִּי אֱלִיעֶזֶר בֶּן תַּדַּאי סָבַר: אֵין בְּרֵירָה, וְרַבָּנַן סָבְרִי: יֵשׁ בְּרֵירָה.
Where they disagree is in the case where they bought a barrel of wine in partnership. Rabbi Eliezer ben Taddai holds: There is no principle of retroactive clarification, i.e., there is no halakhic assumption that the undetermined halakhic status of items can be retroactively clarified. Consequently, after the wine is consumed, it is not possible to clarify retroactively which portion of the wine belonged to each person. Therefore, they cannot each be said to own a particular part of the wine, which renders it unfit for an eiruv. But the Rabbis hold that there is retroactive clarification, and therefore they may rely on this partnership to establish an eiruv.
רַב יוֹסֵף אָמַר: רַבִּי אֱלִיעֶזֶר בֶּן תַּדַּאי וְרַבָּנַן בְּסוֹמְכִין עַל שִׁיתּוּף בִּמְקוֹם עֵירוּב קָמִיפַּלְגִי.
Rav Yosef said that this dispute should be understood differently, as Rabbi Eliezer ben Taddai and the Rabbis disagree about whether one may rely on a merging of an alleyway instead of an eiruv, i.e., whether the merging of an alleyway to permit carrying in the alleyway, exempts the courtyards that open into the alleyway from having to establish an eiruv for the purpose of carrying from one courtyard to the other.
This Tanna, Rabbi Eliezer ben Tadai is relatively rare. One of the few other instances he is quoted comes from a three way machlokes in how to interpret the Shira that the Jews sang at Yam Suf (Mekhilta Derabbi Yishmael 15:1):
ויאמרו לאמר, ר' נחמיה אומר שרת רוח הקדש על ישראל ואמרו שירה כבני אדם שהן קוראין את שמע. ר' עקיבא אומר רוח הקדש שרת על ישראל ואמרו שירה כבני אדם שהן קוראין את ההלל. ר' אליעזר בן תדאי אומר משה היה פותח בדברים תחלה וישראל עונין אחריו וגומרין עמו. משה היה פותח ואומר אשירה לה' וישראל עונין אחריו וגומרין עמו אשירה לה' כי גאה גאה משה היה פותח ואומר עזי וזמרת יה וישראל עונין אחריו וגומרין עמו עזי וזמרת יה ויהי לי לישועה, משה היה פותח ואומר ה' איש מלחמה וישראל עונין אחריו וגומרין עמו ה' איש מלחמה ה' שמו:
(Exodus, Ibid.) "And they said, saying": R. Nechemiah says: The Holy Spirit reposed upon them and they intoned song as one reciting the Shema (i.e., one, beginning, and the other continuing). R. Akiva says: As men reciting the Hallel. R. Eliezer b. Tadai says; Moses would begin with his words, and Israel would respond (with theirs). Moses would begin: "I shall sing to the L-rd," and Israel would end with him and respond: "I shall sing to the L-rd for He is high on high. Horse and its rider He cast into the sea." Moses would say (2) "The strength and vengeance of the L-rd" and Israel would end with him and respond "The strength and vengeance of the L-rd has been salivation to me." Moses would begin (3) "The L-rd is a man of war," and they would end with him: "The L-rd is a man of war; the L-rd is His name."
I would like to suggest that Rabbi Eliezer ben Tadai is leshitaso consistent. In this Midrash we have three opinions about how the Az Yashir was sung. Rav Nechemia said Moshe began, and then another one continued, and another continued. Rabbi Akiva said the Jews recited it in unison like Hallel. Rabbi Eliezer ben Tadai says Moshe would start a verse, but the Jews would then repeat the beginning of the verse and continue to the end.
While I cannot figure out the significance of this three way machlokes, it is interesting to note that Rabbi Eliezer ben Tadai opinion that the Jewish people’s words mixed with Moshe’s, but Moshe’s words did not miix with the Jewish people -- That is the Jews said the full verse while Moshe said only part. Somehow this is parallel to Shituf not working for chatzer vs. it working.
for Video Shiur click here to listen: Psychology of the DAF Eruvin 71
Translation Courtesy of Sefaria
Translations Courtesy of Sefaria, except when, sometimes, I disagree with the translation 
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