Siman 416

We hold in Eruvin (38b) that Shabbat and Yom Tov adjacent to one another—such as when Yom Tov falls on the eve of Shabbat or on Sunday—are two separate sanctities. That is to say, the two days of Yom Tov of Pesach, Shavuot, and Sukkot, which are called the Yom Tov of the Diaspora because in Eretz Yisrael they observe only one day, are two separate sanctities, for only one of them is truly holy, and we observe two days due to doubt. However, the Yom Tov of Rosh Hashanah is one sanctity, and is like a single long day, for the reason that will be explained elsewhere. Regarding Shabbat and Yom Tov, there is a dispute in the Gemara there, and the halacha was decided that they are two separate sanctities; therefore, they have no connection to one another.

Therefore, a Yom Tov adjacent to Shabbat, whether before it or after it, and similarly the two days of Yom Tov of the Diaspora—a person can make an eruv for two directions: the first day to the east of his house, and the second day to the west of his house. And he relies on whichever of them he desires for the first day, and on the eruv in the second direction for the second day, and he places both of them on the eve of Yom Tov. And similarly, he can make an eruv for the first day, and on the second day he will be like the residents of the city, or on the first day like the residents of the city, and on the second day the eruv shall take effect. And on the day that he is like the residents of the city—he has two thousand amot in every direction from his city, and on the day the eruv takes effect—he has two thousand in every direction from the location of the eruv. And he recites a blessing over both of them and says: 'With this eruv it shall be permitted for me to walk on one of the two days in this direction,' and similarly regarding the second eruv, and tomorrow he will clarify for whichever he desires, for we have already written that regarding techumin there is bereirah, because it is of rabbinic origin.

And this is on Shabbat and Yom Tov and on the two days of Yom Tov of the Diaspora. But on Rosh Hashanah, since the two days are as one day—he can only make an eruv for both days, and if he made an eruv for one day, it is like making an eruv for half a Shabbat—and it is not an eruv. And so too he may make a condition on his eruv, and say: "My eruv shall be for this Shabbat and not for another Shabbat," or "for another Shabbat and not for this Shabbat." And so too "my eruv shall be for Shabbats and not for Yamim Tovim," "for Yamim Tovim and not for Shabbats." And if he wishes, he may make one eruv also for Shabbat and Yom Tov and for the two days of Yom Tov of the Diaspora, for both days in one direction. However, against this there is a stringency, for every day requires the acquisition of the place of rest for itself, since they are separate from one another, and how shall he acquire the place of rest from one for the other, and this is like the acquisition of the place of rest on Thursday for the day of Shabbat, which is not the case on Rosh Hashanah.

Therefore, on Yom Tov and Shabbat, and on the second day of Yom Tov in the Diaspora, when one makes an eruv with bread—the eruv must be whole also during the twilight of the first day, and if it was lost, he has no eruv for the second day. Therefore, one who makes an eruv with bread, how does he act: he brings it on the eve of Yom Tov or on the eve of Shabbat and remains with it until dark, and takes it in his hand if it was the night of Yom Tov, and comes to his home. And the next day, he brings it to that place and leaves it there until it grows dark, and eats it if it was the night of Shabbat, or brings it if he wishes when it was the night of Yom Tov. If it was eaten on the first day—it is an eruv for the first day but not for the second.

And if he established the eruv with his feet—he must establish the eruv on the first and on the second. And this means that on the first day he must be there during bein hashemashot, and he should think in his heart that he shall acquire residence there. But he shall not say anything, because it is forbidden to make any preparation from Yom Tov for Shabbat, or from Shabbat for Yom Tov, or from the first day of Yom Tov for the second, even with mere speech. And all the more so that he cannot establish an eruv with bread that he did not use for an eruv on the first day, because he would need to designate it as an eruv, and it would turn out that he is preparing from today for tomorrow, and if he did establish the eruv—it is not an eruv. But regarding the speech, if he spoke—it is an eruv. (Magen Avraham, subsection 2)

This is the rule: If one made an eruv on the first day with food, if he wishes to make an eruv with his feet on the second day—it is a valid eruv. And he should do so through thought; and if he spoke—it is not a hindrance. But if he wishes to make an eruv with bread on the second day as well—he must make the eruv specifically with the same bread with which he made the eruv on the first day, for he does not need to say anything, as he has already designated it as an eruv, and if so, he is not preparing anything. And if he made an eruv with other bread—it is not an eruv. And also, that which is permitted with his feet on the second day is only when he made an eruv on the first day, either with bread or with his feet. But when he did not make an eruv at all—it seems to me that it is forbidden to make an eruv with his feet on the second day even without speech, for this would be a complete preparation and a new matter, as this is explicitly implied by the language of the Shas (39a) which says: "If he made an eruv with bread on the first day—he may make an eruv with his feet on the second day." That is to say, even though there is a change from an eruv of bread to an eruv of feet—because in any event it was designated as an eruv on the first day, and the preparation is not so recognizable. This is not the case if he did not make an eruv at all on the first day—he cannot make an eruv on the second day with anything, and if he made an eruv—it is not an eruv, because this is a great preparation. (So it seems to me)

And all this is regarding Shabbat and Yom Tov and regarding the two festival days of the Diaspora. However, regarding the two festival days of Rosh Hashanah—one establishes an eruv on the eve of Yom Tov for both days, and even if it was eaten on the first day, it remains an eruv for the second. Similarly, if one established an eruv with his feet on the first day, he does not need to establish an eruv with his feet on the second, and this is the opinion of the Rambam in chapter 8. The Ra'avad there disagrees with him, and holds that only for stringency do we say that it is one sanctity, and not for leniency; therefore, one must establish an eruv with his feet also on the second day. Likewise, if one established an eruv with bread on the first day and it was eaten, he has no eruv for the second, see there. But most of the poskim agreed with the Rambam, for the sages treated it entirely as a single long sanctity, and behold, this is not a Torah prohibition, and techumin are rabbinic. And they ordained the mitzvah of eruvei techumin, and they said that it is one sanctity whether for leniency or for stringency, and so ruled the Tur and the Shulchan Aruch.

And know, that which they said that one may mix two eruvin from two directions for the two days—this is specifically when it would be possible for him to reach each of the two eruvin on the first day. But if it is impossible for him to reach the eruv of the second day on the first day—it is not an eruv for the second, for we require that the eruv be a meal that is fit while it is still day. And even though regarding the two days of Yom Tov in the diaspora it is a "from whatever [perspective]"—if the first is a weekday, he may go to his eruv, and if the first is holy, then the second is a weekday and does not require an eruv—nevertheless, since ultimately he cannot reach the eruv on the first day due to the doubt, it is not an eruv (Magen Avraham, subsection 3).

Therefore, one must be careful not to place the eruvin very far apart. How so? If one placed his eruv for the first day at the end of two thousand cubits to the east, and placed the second eruv for the second day to the west—it is not an eruv even if he placed it nearby, for he cannot reach it while it is still day, as nothing remains for him toward the western side. But if he placed it for the first day fifteen hundred cubits to the east, behold, five hundred cubits remain for him toward the western side—he may place it for the second day toward the western side up to five hundred cubits and no more, for with this measure he can come to his eruv of the second day on the first day. And Yom Kippur is like Shabbat, whether regarding eruvei chatzerot or regarding eruvei techumin, and one may also make an eruv with bread. For even though he cannot eat—nevertheless it is fit for a child, as we do not require a meal fit specifically for him, as was written in siman 409. And Yom Tov—eruvei techumin applies to it but not eruvei chatzerot, and the reason for the matter we explained in siman 397, section 4; see there.