The Shulchan Aruch (Orach Chaim 630:12) rules, that one may use his friend as one of the walls of the succah, even on Yom Tov. However, the friend isn’t allowed to know that he is being used for the mechitzah [wall]. In the week, however, even if the friend knows about it, it’s ok.
The question is, if one is being used as a wall of the succah, is he allowed to eat in the succah, or do we say that since he doesn’t have succah walls - as he is the walls - it’s forbidden for him to eat in this succah?
The Oiver Oirach (Aderes in his Hago’as on the Orchos Chaim siman 630) is in unsure about the above.
He cites proof from the Gemara in Eruvin (44a). the Gemara in Eruvin concludes that the beraisa which allows a person to act as a wall for the succah is like Rebbi Eliezer. This same Rebbi Eliezer holds in Succah (27a) that one must use the same succah for all seven days of Succos and one can’t keep changing which succah he uses.
If the person being used as a wall isn’t allowed to eat in the succah, then he will need to go and eat in a different succah. If so, when he leaves the succah he is being the wall of, that succah will become pasul [disqualified] as it isn’t fit for seven days. Therefore, it must be that the person acting as a wall can eat in the succah.
However, he refutes the proof, as there is a big question on the opinion of Rebbi Eliezer. Rebbi Eliezer holds (Succah 27b, 31a) that one can’t fulfil the mitzvah of succah using a borrowed succah. If, so, how can a person be used for a succah wall, surely one doesn’t own him? Even when it comes to little children we don’t say that the parent owns them (Eruchin 28a)? It must be, that the person being used for the succah wall is an eved [slave] and by slaves we say that they are owned by their masters. If, we are talking about a slave, then our proof falls away, as slaves are exempt from eating in the succah.
R’ Zilberstein (Chasukei Chemed Shabbos 99b) tries to bring proof from the Shulchan Aruch which says: יכול לעשות מחבירו דופן לסוכה להכשירה – “One can use his friend as a wall for the succah”. Why does the Shulchan Aruch only mention a friend, why can’t the person himself be the wall?
However, he refutes this proof, as on Shabbos and Yom Tov one can only be a mechitzah if he doesn’t know about it, and if one would be the mechitzah himself then obviously he would know about it. Therefore, the Shulchan Aruch specifically mentioned the case of a friend.
The Sefer Vayishmah Moshe (R’ Moshe Fraund pg. 167) brings that R’ Mordechai Gross shlita asked this question to R’ Elyashiv and he said that it’s contradictory, and one can’t be both the wall and at the same time eat in the succah. (This riddle was adapted from Madanay Asher)
