QUESTION: The Gemara teaches that if one forgets to make an Eruv Tavshilin on Wednesday before a two-day Yom Tov that begins on Thursday, he may make the Eruv on Thursday (Yom Tov) with a condition (Tenai) by saying, "If today is not really Yom Tov and tomorrow is, then I am making the Eruv today, and if today is Yom Tov and tomorrow is not, then I do not need an Eruv to cook tomorrow for Shabbos."

The RAMBAM (Hilchos Yom Tov 6:12) cites this Halachah, but he adds (6:14-15) that nowadays -- when the two days of Yom Tov are observed not because of a doubt but because of the enactment of "Minhag Avoseinu" -- "one may not make an Eruv with a Tenai... but rather it must be done only on Erev Yom Tov."

The RA'AVAD says that while the Rambam's ruling has logical basis, there is no source for such a ruling in the Gemara or among the earlier Poskim. He therefore rules that one is permitted to make an Eruv with a Tenai on the first day of Yom Tov nowadays as well.

What is the logic of the Rambam's ruling? Why should one not be allowed to make an Eruv with a Tenai today? In the times when Beis Din established the new month based on the testimony of witnesses, the Jews in Chutz la'Aretz observed a second day of Yom Tov due to the doubt about when Beis Din declared the new month. Today, the Jews in Chutz la'Aretz observe a second day of Yom Tov not out of doubt, but because of "Minhag Avoseinu." If our forebears were permitted to make an Eruv Tavshilin with a Tenai on the first day of Yom Tov, then certainly we, who observe the second day of Yom Tov only because they did, should be permitted to make an Eruv Tavshilin with a Tenai on the first day of Yom Tov. After all, the "Minhag Avoseinu" includes the Minhag to permit making an Eruv with a Tenai on Yom Tov. Why do we observe the second day of Yom Tov in a more stringent manner than our forebears?

Second, the Rambam himself (Hilchos Yom Tov 1:24) rules that an egg laid on the first day of Yom Tov is permitted on the second day of Yom Tov, as the Gemara earlier (4b) teaches. From the fact that the Rambam does not differentiate between nowadays and earlier times it is evident that he maintains that the second day of Yom Tov is not more stringent nowadays than in days of yore. The fact that the egg is permitted on the second day of Yom Tov nowadays shows that the two days of Yom Tov are not one long Kedushah, but rather two separate Kedushos, just as they were when the second day of Yom Tov was observed due to a doubt. Since they are two separate Kedushos, one should be able to make an Eruv with a Tenai on the first day of Yom Tov.

(a) The LECHEM MISHNEH explains that there is an important difference between making an Eruv Tavshilin with a Tenai nowadays and making it with a Tenai in the times when the second day of Yom Tov was a genuine Safek. In order to make the Eruv Tavshilin, one must express a condition, just as his ancestors used to do. They used to say, "If today is not really Yom Tov and tomorrow is, then I am making the Eruv today, and if today is Yom Tov and tomorrow is not, then I do not need an Eruv to cook tomorrow for Shabbos." They had a genuine doubt as to which day was Yom Tov. Hence, they were able to make such a conditional statement. Nowadays, however, one knows for certain that the first day is Yom Tov, and thus he cannot make a conditional Eruv by saying, "If today is not really Yom Tov and tomorrow is, then I am making the Eruv today," because that is not a true statement. He knows that the first day is Yom Tov and that there is no doubt. On the other hand, he cannot say, "Since today is definitely Yom Tov, tomorrow is definitely not Yom Tov and therefore I may cook tomorrow," because the Rabanan instituted that a second day of Yom Tov be observed with all of the laws of Yom Tov. Therefore, no condition can be applied in order to make an Eruv Tavshilin.

In contrast, when an egg is laid on the first day of Yom Tov, one does not need to make any sort of conditional statement in order to partake of the egg on the second day. One may observe the Minhag Avoseinu and eat the egg on the second day of Yom Tov.

(b) RABEINU CHAIM HA'LEVI explains that the reason why the Rambam does not allow one to make an Eruv with a Tenai on the first day of Yom Tov is not because the statement of the Tenai is false, but because the Tenai cannot take effect because the first day certainly is Yom Tov. He explains that not only is the status of the first day more stringent today than it used to be (when it was observed as a doubt), but even the status of the second day is more stringent today than it was in the times when it was observed out of doubt. This is because the Rabanan enacted a decree that the day be observed as Yom Tov as a Safek, a doubt. The status of the second day of Yom Tov, therefore, has a greater element of certainty, and thus a Tenai cannot take effect.

Why, then, is an egg laid on the first day of Yom Tov permitted on the second day? Both days should be considered days that are definitely Yom Tov and the egg should be prohibited, just as an Eruv Tavshilin cannot be made with a Tenai for this reason. Rabeinu Chaim answers that when each day is viewed independently, each one can be considered definitely Yom Tov. Only when the two days are viewed together as a pair must one of them be considered not a definite day of Yom Tov. When an egg is laid on the first day of Yom Tov, in order to determine whether it is permitted on the second day requires that both days be viewed together, because it is the preparation of the egg (Hachanah) from one day of Yom Tov to the next that would prohibit it. When the two days of Yom Tov are viewed as a single, two-day unit, only one of the two can be considered definitely Yom Tov.

OPINIONS: The Gemara says that the Halachah follows the view of Beis Hillel in the Mishnah, who says that one may make an Eruv Tavshilin by setting aside only one Tavshil (cooked dish) before Yom Tov as the Eruv.

What is the source for the common practice today to set aside both a cooked food and a baked item (Chalah or Matzah)?

(a) RABEINU TAM (cited by Tosfos) writes that even Beis Hillel agrees that setting aside a cooked food permits one only to cook, fry, and boil (that is, to heat a food through the medium of a liquid) on Yom Tov for Shabbos. It does not permit one to bake (with dry heat) on Yom Tov for Shabbos. If one wants to bake on Yom Tov for Shabbos, he must set aside a baked item before Yom Tov.

Rabeinu Tam proves this from the Beraisa (15b) in which Rebbi Eliezer derives from the verse (Shemos 16:23) that a person must have already baked something for Shabbos prior to Yom Tov in order to be permitted to bake more on Yom Tov for Shabbos, and one must have already cooked something for Shabbos prior to Yom Tov in order to be permitted to cook more on Yom Tov for Shabbos. The Beraisa clearly says that one must set aside a baked item in order to bake on Yom Tov for Shabbos.

This is also implied by the Mishnah which mentions only cooking and not baking ("one may not cook on Yom Tov for Shabbos... unless one prepared a cooked item on Erev Yom Tov"). The Mishnah does not say that one is permitted to bake based on having set aside a cooked food.

How does Rabeinu Tam understand Chananyah's statement? Chananyah said that while Beis Shamai maintains that in order to be permitted to cook on Yom Tov for Shabbos one must set aside a cooked item before Yom Tov, and in order to bake one must set aside a baked item, and in order to insulate boiling water one must set aside insulated water before Yom Tov, Beis Hillel argues. Rabeinu Tam rules that one needs to set aside a baked item in order to be permitted to bake, but this seems to be the opinion of Beis Shamai and not Beis Hillel! Rabeinu Tam explains that Beis Hillel argues with Beis Shamai only with regard to insulating boiling water on Yom Tov. Beis Hillel maintains that insulating boiling water is included in cooking, and thus setting aside a cooked item suffices to permit one to insulate water on Yom Tov for Shabbos. Beis Hillel agrees, however, that in order to bake, one must set aside a baked item before Yom Tov.

How does Rabeinu Tam understand the Gemara (16a) in which Abaye says that one may not use bread for an Eruv Tavshilin? Rabeinu Tam explains that Abaye means that one may not use bread instead of a cooked item to permit cooking. He certainly agrees that to permit baking one must set aside bread before Yom Tov.

This is also the opinion of the BA'AL HA'ME'OR, RA'AVAD, and ME'IRI. This is the source for the common practice to set aside both a cooked dish and a loaf of bread for the Eruv Tavshilin.

(b) The RI disagrees and maintains that a single cooked dish certainly suffices to permit both cooking and baking. The Beraisa (15b) which mentions preparing a baked item for baking and a cooked item for cooking is the opinion of Rebbi Eliezer. The Yerushalmi here cites the rest of the Beraisa in which Rebbi Yehoshua disagrees and says that setting aside a baked item suffices for both cooking and baking. In general, when Rebbi Eliezer and another Tana argue, the Halachah follows the other Tana because Rebbi Eliezer is "Shamuti" (a disciple of Beis Shamai; Yerushalmi, cited by TOSFOS to Shabbos 130b), and in this case, too, Rebbi Eliezer expresses the opinion of Beis Shamai as quoted by Chananyah.

This interpretation of the view of Beis Hillel is also supported by the Tosefta (2:2), and it is the ruling of RABEINU CHANANEL (17b), the RAMBAM (Hilchos Yom Tov 6:1), the RAMBAN and other Rishonim.