We have learned that in order to create an eiruv that would allow residents of the houses surrounding the courtyard to carry on Shabbat, the residents all need to become partners in food which will legally create a common community among them.
The Mishna on our daf discusses a case where a business relationship – a partnership between neighbors – already exists.
If a homeowner was in partnership with his neighbors, with this one in wine and with that one in wine, they need not establish an eiruv, for due to their authentic partnership they are considered to be one household, and no further partnership is required.
If, however, he was in partnership with this one in wine and with that one in oil, they must establish an eiruv. As they are not partners in the same item, they are not all considered one partnership. Rabbi Shimon says: In both this case and that case, i.e., even if he partners with his neighbors in different items, they need not establish an eiruv.
In the Gemara, Rav emphasizes that the case where the business partnership can, itself, be considered an eiruv would only be if the wine was all in one barrel. If, however, there were two separate partnerships, each one with its own barrel of wine, the tanna kamma (first) would not consider that relationship enough to act as an eiruv.
Rav Shmuel Strashon in his commentary to the Gemara (known as the Rashash) points out that Rav’s explanation is based on the fact that we need to have a relationship between all parties in order for the partnership to have the effect of an eiruv. If one person is a partner separately with each neighbor, we do not have a true “community.” Therefore the business partnership will only serve the purpose of an eiruv if all three of them are joined together – by virtue of a single barrel of wine.