It is clear that a person cannot set up two eiruvin that will allow him to travel outside the precincts of the city in one direction in the morning and in the opposite direction in the afternoon. The Mishna (38a) presents a case where Yom Tov immediately precedes Shabbat. In such a case, can an eiruv be set up to allow travel in one direction for Yom Tov and in the other direction for Shabbat? Rabbi Eliezer rules that such arrangements can be made, as Shabbat and Yom Tov are separate entities. The hakhamim, however, believe that they should be considered as having kedusha ahat – that they share the same element of holiness – and whatever is established at the beginning of the holiday remains in force until after Shabbat.
In this case, Rav rules that the halakha follows the opinion of Rabbi Eliezer, as four sages are known to accept that position. Our Gemara lists the names of the four sages – Rabban Shimon ben Gamliel, Rabbi Yishmael the son of Rabbi Yoḥanan ben Beroka, Rabbi Elazar son of Rabbi Shimon and either Rabbi Yosei bar Yehudah or Rabbi Elazar – but does not quote their ruling. The Jerusalem Talmud quotes their ruling as referring to someone who placed an eiruv at the beginning of Yom Tov, which was eaten or destroyed before the onset of Shabbat. According to these sages, the eiruv cannot be relied upon for Shabbat, since the separate kedusha of Shabbat demands a separate eiruv.
This ruling of Rav is followed in the Gemara by a question presented by Rav Hisda.
Did Rav actually say: The halakha is in accordance with the opinion of the four Elders and in accordance with the opinion of Rabbi Eliezer, who said that when Shabbat and a Festival fall out on consecutive days, they constitute two distinct sanctities?Wasn’t it stated that with regard to a case where Shabbat and a Festival occur on consecutive days, Rav said: An egg that was laid on one is prohibited on the other, just as an egg that was laid on a Festival day is prohibited on that same day? This statement indicates that the two days constitute a single sanctity. How, then, can he say here that the halakha is in accordance with the opinion that they are two distinct sanctities?
Rabba answers that this ruling is based on a different halakha, that all preparations for Shabbat need to be done on a non-holiday, so that an egg born on Yom Tov cannot be used on Shabbat even if they are separate kedushot, since that would be preparing for Shabbat on Yom Tov.
Rav Hisda’s question is introduced with a curious statement – “When Rav Huna passed away, Rav Hisda entered the beit midrash and pointed out a contradiction within Rav’s rulings.” Rav Tzvi Hirsch Chajes explains that due to a misunderstanding, the relationship between Rav Huna and Rav Hisda was tense, and they did not interact for many years. Therefore Rav Hisda did not enter the Bet Midrash to raise a question on Rav Huna’s mentor, Rav, until after Rav Huna had passed on.