Reuven and Shimon shared an apartment.
One day, while Reuven was at his parents’ home, he called Shimon. “I have an old printer that I’m giving away,” Reuven said. “Do you want it?”
“What condition is it in?” asked Shimon.
“The printer works OK,” said Reuven, “but my father’s office upgraded their printers. They let him take one of the old ones, which is much better than mine.”
“I certainly am interested,” said Shimon. “As you know, my printer has been making problems recently.”
Reuven brought the printer to the apartment that evening. “Here is the printer!” he said to Shimon.
“Thank you,” said Shimon. “Please just leave it on the floor in the living room near my computer.”
That evening Reuven’s father called him. “I was using the printer that I brought from the office,” he said. “It had a short and stopped working. You should bring your printer back.”
“Oh,” said Reuven, “I gave it to Shimon.”
“You handed the printer to him already?” asked Reuven’s father.
“Actually, Shimon said to put the printer on the floor,” said Reuven, “but I told him that I brought it for him.”
“I normally would expect you to uphold your word,” said Reuven’s father, “but you offered the printer because you thought it was extra; now you still need it.”
“But I placed the printer in the apartment with intention that it should be Shimon’s,” said Reuven. “He may have already acquired it! We are learning now in yeshiva about kinyan chatzer, acquisition through one’s property.”
“If it already became his, that’s a different story,” said Reuven’s father. “But it’s not just his apartment; you share it with him. I suggest that you clarify this with Rabbi Dayan.”
Reuven called Rabbi Dayan and asked:
“Did Shimon acquire the printer? Can I retract from the gift?”
“Indeed, the Gemara (B.M. 11a) teaches that a person’s property can acquire for him,” replied Rabbi Dayan (C.M. 200:1; 243:20-21).
“Elsewhere, the Gemara (B.B. 84b) discusses the case of a seller who measures food into the buyer’s basket that is sitting in joint property (C.M. 200:7).
“Ketzos (176:1; 260:1) proves from this gemara that only when measured into his basket does the buyer acquire in the joint property. However, were the seller to place the item on the ground of the shared property, the implication is that the buyer does not acquire it through kinyan chatzer. (Nonetheless, Ketzos suggests that if one partner were to place items there with intention that they become assets of the partnership, the joint property would acquire for the partnership.)
“Some Acharonim explain this gemara is based on the idea that joint property belongs to whichever partner is using it at that moment. Thus, if the buyer places his basket there, the area underneath is currently his, so that he can acquire in his basket. However, if the seller placed his item there, that area is temporarily his, so that the buyer cannot acquire there through kinyan chatzer” (Nesivos 176:2).
“Machaneh Ephraim (Hil. Kinyan Chatzer #6) suggests, though, that if the seller initially places the item there with intention to sell or give it to the buyer, the buyer would acquire it, since the seller places it there with intention that the area underneath should now serve the buyer to acquire the object” (Pischei Choshen, Shutafim 8:26).
“Thus, according to the Ketzos, the transaction was not completed, and you can retract from the gift, whereas according to Machaneh Ephraim, Shimon already owns it. Due to the dispute, you can still reclaim the printer.
“Nonetheless,” concluded Rabbi Dayan, “it is considered untrustworthy – mechusar amanah – to back off from one’s word without good reason – which exists here” (C.M. 204:7-8,11; 241:1; Pischei Teshuvah 207:5).
Verdict: Partners cannot sell or give one to another in joint property through kinyan chatzer, but if the item was initially placed in the joint property with intent for the transaction, there is a dispute whether it is valid.