Gemara

Question: (When a Shechiv Mera may retract,) if he retracted part of the gift, is this a retraction of the entire gift?

Answer (Beraisa): If Reuven said 'I give all my property to Ploni. I give some of it to Almoni', Almoni acquires, but Ploni does not.

Suggestion: Almoni acquires after Reuven dies, but Ploni does not. Retracting part of the gift to Ploni (i.e. what he gave to Almoni) is a retraction of the entire gift.

Rejection: No. The case is, Reuven recovered. (The gift to Almoni was partial, therefore Reuven cannot retract from it.)

Support (Seifa): If he said 'I give some of my property to Ploni. I give all of it to Almoni', Ploni acquires, but Almoni does not.

Granted, if Reuven recovered, he can retract. However, if Reuven died, both should acquire! (Reuven gave all his property. 'I give all of it to Almoni', means the rest!)

Objection (Rav Yemar): Even if the entire Beraisa discusses when he recovered, it shows that a partial retraction is a full retraction!

If it is a full retraction, this explains why Almoni acquires.If it were not a full retraction, Reuven gave all his property, and he would be able to retract also the gift to Almoni!

The Halachah is, a partial retraction is a full retraction.

We can explain the Reisha whether Reuven died or recovered. In the Seifa, we must say that he recovered.

Rishonim

Rif and Rosh (9:22):The Halachah is, a partial retraction is a full retraction. A Beraisa teaches that if Reuven gave all his property to Ploni, and then some to Almoni, only Almoni acquires. If he gave some to Ploni, and then all to Almoni, only Ploni acquires. The Reisha is whether or not Reuven recovered. In the Seifa, we must say that he recovered. If not, Ploni would acquire his gift, and Almoni would acquire the rest! We must say that they did a Kinyan to acquire from him.

Nimukei Yosef (DH Ibo'i): The Gemara says that a partial retraction is a full retraction. This is not when he explicitly said that he retracts only from part. Then, surely the first keeps the rest of the gift. Even though now it is a partial gift, which (normally) requires a Kinyan, it depends on the time he gave. At the time, he gave through words, and if he died, Ploni would acquire everything. If he gave to two people and later retracted from one of them, this is a retraction from the other, since both were in one document. If one wrote some of his property to others and some to his heirs, and retracted regarding his heirs, the gift to others stands, for a gift to heirs is like a mere inheritance. The Ritva says so in the name of the Rif and Ramban. I say that this is when what he took back from his heirs, he gave to others, for he must give away all his property. If he kept part for himself, he showed that it is not Matnas Shechiv Mera, rather, a healthy person's gift, so it cannot work without a Kinyan.

Rambam (Hilchos Zechiyah 9:17): If a Shechiv Mera (Reuven) partially retracted, this is like a full retraction. If Reuven gave all his property to Ploni, and did a Kinyan for Yifuy Ko'ach (to give greater rights), and then gave part to Almoni, and did a Kinyan for Yifuy Ko'ach, Almoni acquires, but Ploni does not. This is whether or not Reuven recovered.

Rambam (18): If he gave some to Ploni and did a Kinyan for Yifuy Ko'ach, and afterwards gave all to Almoni and did a Kinyan for Yifuy Ko'ach, if Reuven died, Ploni acquires his gift, and Almoni acquires the rest. If Reuven recovered, Ploni acquires, but Almoni does not acquire.

Poskim

Shulchan Aruch (CM 250:12): If a Shechiv Mera (Reuven) partially retracted, presumably he fully retracted.

Rema: Even if he gave to two people in one document, and later retracted from one of them, also the second is Batel.

SMA (34): We do not say that a document is powerful, and his retraction does not show that he retracted also from the first. The Rema discusses in one document, for if there were two, it would not be a retraction regarding the other, for it is in a separate document. This follows from the Nimukei Yosef.

Rema: However, if he specified that he retracts only partially, the first acquires the rest, even though it was a partial gift and no Kinyan was done, for when he gave it it was a total gift and it did not need a Kinyan. Some say that this is only if he went back and gave that part (he retracted from) to others, but if he kept it for himself, also what the first has is Batel, until he does a Kinyan. If one wrote some of his property to others and some to his heirs, and retracted regarding his heirs, the gift to others stands, for the gift to his heirs is like a mere inheritance.

SMA (36): The gift to the others is a partial Matnas Shechiv Mera, and it requires a Kinyan. However, perhaps it is considered a total gift, for initially he gave away everything. If he specified that he does not totally retract, it helps. Here also, even though he did not specify, we say that a retraction from his sons and heirs is not considered retraction. If he kept what he retracted from giving to his heirs, surely the first recipients need a Kinyan. This requires investigation.

Taz (DH k'Yerushah): If what he gave to his heirs is a mere inheritance, what he gave to the others is a partial Matnas Shechiv Mera, and it should require a Kinyan! We must say that since he mentioned heirs, this shows that (he expects to die, and) the part he gave is like a Matnas Shechiv Mera, which does not need a Kinyan.

Shulchan Aruch (ibid): Therefore, if Reuven gave all his property to Ploni, and then gave part to Almoni, Ploni does not acquire even if Reuven dies, for he retracted. Almoni's gift is a partial Matnas Shechiv Mera. If it has a Kinyan, he acquires even if Reuven recovered. If it has no Kinyan, he does not acquire even if Reuven died. If Reuven gave part of his property to Ploni with a Kinyan, and then gave the rest to Almoni, Ploni acquires even if Reuven did not die. Almoni's gift is a total Matnas Shechiv Mera. If Reuven died, Almoni acquires even without a Kinyan. If he recovered, Almoni does not acquire even if there was a Kinyan.

SMA (38): Even if he interrupted between the gifts to Ploni and Almoni, Ploni acquires even if Reuven recovered, because there was a Kinyan. It is not considered a total Matnas Shechiv Mera from which one can retract. Since he said that he gives the rest to Almoni, the gift to Ploni is considered a partial Matnas Shechiv Mera. This is why the Tur and Shulchan Aruch repeated this law. Also if he made a Kinyan for Ploni but not for Almoni, this shows that Ploni's gift was a partial Matnas Shechiv Mera and Almoni's was a total Matnas Shechiv Mera.

Bach (20): Also above (Sa'if 17) the Tur discussed this. There he taught not to say the following. If one gave with a Kinyan, we are not concerned for an interruption, for from the beginning he intended to give away everything and retract if he wants. He interrupted in the middle to think about what to give to everyone. Therefore, if he recovers, even the first does not acquire, even if there was a Kinyan. If he dies, all acquire, even if there was no Kinyan. We do not say all this. Stam, a Shechiv Mera first plans what he will give, and then gives. An interruption shows that he reconsidered, so the first, for whom a Kinyan was done, acquires even if Reuven recovers, like the law of a partial Matnas Shechiv Mera. Above, the primary Chidush was that the first acquires even if Reuven recovered. Here, the primary Chidush is that the latter does not acquire if Reuven recovered, even if there was a Kinyan with Yifuy Ko'ach. The Rashbam said 'and went back and gave...', and the Rambam said 'and afterwards gave' to show that he interrupted in the middle. What the SMA wrote is wrong.

Shach (13): The Bach is correct. I think that the correct text of the SMA should say 'even if he did not interrupt between the gifts. (The SMA explicitly says so in the Prishah (20) - PF.)

Shach (14): The Shulchan Aruch says that if Reuven died, Almoni acquires even without a Kinyan, i.e. and all the more so if there was a Kinyan with Yifuy Ko'ach. A Kinyan without Yifuy Ko'ach weakens the recipient (Magid Mishneh Hilchos Zechiyah 8:21, Beis Yosef Sa'if 17).