Although contracts and agreements usually “seal the deal,” in contemporary law, there are certain circumstances under which the law will allow a buyer to change his mind about the purchase, even after agreeing to it. Our Gemara presents a similar question. Once a kinyan – a symbolic purchase agreement – is made, until when can the parties back out of the deal?
Rabba rules that as long as the two parties are still sitting together, the kinyan can be cancelled; according to Rav Yosef they can only do it so long as they are still discussing that particular matter.
The R”i Albarceloni, quoted by the Ramban and others, brings an opinion that limits this question to the case of a shekhiv me-ra – someone who is on their deathbed – who is instructing the people around him regarding how to dispose of his property after his death. According to this approach, it is only someone like this who may change his mind at any moment whose kinyan would not have full force. Rabbeinu Tam argues that the Gemara’s question applies to all cases and all circumstances.
Most rishonim agree with the position taken by the R”i Albarceloni himself, who limits the possibility of backing out of the agreement only to cases where the kinyan was performed by symbolic means, e.g. a kinyan sudar, where the means of the kinyan was an object that represents the item that was purchased. If the kinyan was meshikha or hagbaha (pulling or lifting the object itself as a show of ownership – see Bava Batra 84), then there would be no opportunity to back out of the agreement. The explanation given for this distinction is one of gemirut da’at – how certain were the parties about the finality of the sale. When the object itself has been taken by the party who is purchasing – or if money has changed hands, then we can be fairly certain that both parties have reached a final understanding that the exchange of ownership has taken place. On the other hand, if there was only a symbolic kinyan, the finality of the agreement is less clear and the Sages allow a small window of opportunity for the parties to cancel the agreement.