There was a certain man who had a son who seized in theft sheaves [keifei] of flax, and the father took a vow prohibiting his son from deriving any benefit from his possessions. They said to the father: And if the son of your son would become a Torah scholar, and you would want him to be able to inherit your possessions, what would you do? He said to them: Let this son of mine acquire the possessions, and only if the son of my son becomes a Torah scholar then let him, my grandson, acquire them from my son. They asked: What is the ruling?
אמרי פומבדיתאי: ״קני על מנת להקנות״ הוא, וכל ״קני על מנת להקנות״ — לא קני.
The rabbis of Pumbedita say: This is just as if he stated: Acquire the property on the condition that you transfer it to your son. In such a case he has not given anything to the recipient, but has merely made him a conduit to transfer the item to someone else. And in any case where one says: Acquire this item on the condition that you transfer ownership, the recipient does not acquire the item, and the statement has no effect.
ורב נחמן אמר: קני, דהא סודרא ״קני על מנת להקנות״ הוא.
But Rav Naḥman said: He does acquire, as an acquisition by means of a cloth is a case of an act of acquisition performed only in order to transfer ownership. In such a case, one gives another a cloth in order to confer ownership of some other item, but the cloth itself does not assume new ownership. Still, this is an effective means of acquisition. So too, the property of the grandfather may be effectively conferred upon the grandson through the son, without the son acquiring it himself.