פירוש על עירובין 7:7

נתמעט האוכל – from its measurement that is explained further in our Mishnah (i.e., in Mishnah 8).

Introduction This mishnah is a continuation of yesterday’s mishnah which discussed how one sets up an alley partnership.

מוסיף ומזכה – if he comes to add from his own [food or wine], even from a different species [of food] from the first partnership/shared species, he adds and causes them to take possess and he doesn’t need to inform them (i.e., the other participants in the partnership alleyway), for since there remains a bit from the first species, it doesn’t appear like it an Eruv was made at the outset, but if he puts in from the partnership/shared species [of food], even if it was completely finished, he brings from the same species and he doesn’t need to inform them.

If the food was reduced, he must add to it and confer possession [upon the other residents] but he need not inform them. In tomorrow’s mishnah we will learn that there is a minimum amount of food that is necessary for the eruv to be valid. If the amount of food is reduced (before Shabbat begins) he (or another one of the residents) must add to it to make it reach the minimum measure. He must confer ownership of this extra food upon the other residents of the alley, in the same way that he did when he set up the eruv to begin with. However, since he already announced that he was setting up an alley partnership, and thereby let all of the residents know that he was including them, he need not inform them that he is adding to the food.

נתוספו עליהם דיורים מוסיף ומזכה וצריך להודיע – and especially at the time when the courtyard has two openings for two alleyways, for when they make an Eruv with the people of this alleyway, it is forbidden to use another alleyway, therefore it is necessary to inform them, for perhaps it is not satisfactory for them to acquire in this direction and to effect a possession in the direction that is opposite it, but if it lacks an opening other than to this alleyway that they have participated/shared in from the outset, there is no need to inform, because you may obtain a privilege in behalf of a person in his absence, but you cannot act in his behalf to his disadvantage (see the conclusion of Tractate Eruvin, Chapter 7, Mishnah 11, where this phrase is used).

If the number of residents has increased, he must add food and confer possession [upon them], and he must inform them. As we will learn tomorrow, the size of the eruv is somewhat related to the number of residents in the alley. If between when he set up the eruv and the beginning of Shabbat the number of residents increased (this is admittedly unlikely) he might have to increase the food in the eruv. When doing this he must again confer possession upon them and in this case he must inform them of what he is doing, because some of the residents were not there when he made his original announcement.