Gemara

(Rava): Chachamim learn from "Yakir" that a man is believed about who is his Bechor (when we have no Chazakah).

Question: Is this needed in order to give to him an extra portion? One can give his money to whomever he wants!

Answer: He must establish him to be the Bechor in order that the son will receive an extra portion in money that the father will receive (after this).

Question: According to R. Meir, one can transfer ownership of something that is not yet in the world. He can give now an extra portion in money he will get later. Why do we need the verse?

Answer: It enables him to give an extra portion in property that the father will receive when he is Goses (deathly sick. Most Gosesim die.)

Gitin 28a (Mishnah): If Reuven made a Shali'ach to give a Get, (even) if he was old or sick, the Shali'ach gives the Get. We rely on the Chazakah that Reuven is still alive.

(Rava): This is if Shimon was was less than 80 years old, and only moderately sick, but not if he was at least 80, or Goses, for most Gosesim die.

70b (Shmuel): If a man's windpipe and foodpipe were cut, and he gestured to witnesses to write a Get for his wife, they write and give it;

(Beraisa): If a man was found cut up or hanging, and he gestured to witnesses to write a Get, they write and give it.

(Mishnah): If a man became unable to speak, and others asked him if we should write a Get for his wife and he nodded his head, we test him. If he answers properly, we write and give the Get.

71a (Beraisa): Just like we test him to give a Get, we test also regarding sales and gifts, for testimony, and for inheritances.

Erchin 6b: All agree that a Goses he can vow, be Ma'arich (vow to Hekdesh a certain amount based on a person's age and gender) and be Makdish.

Rishonim

Rosh (Kidushin 4:16): Rashi explains that believing the father enables him to give an extra portion in property that the father will receive when he is Goses. Had he said 'what I will receive when I am Goses is to my son', it would not work, for when he gets the property, he cannot give it. R. Chananel explains similarly. Most Gosesim die, so he is considered dead, and he cannot give. Therefore, had he said 'what I will receive when I am Goses is to my son', it would not work. However, regarding inheritance he is alive. What he receives then is considered Muchzak, and not Ra'uy, and the Bechor gets a extra share of it. R. Yo'el derived from here that a Goses cannot divorce, even if his mind is settled, for the Torah says "he will give in her hand." He must be able to give. A Tosefta (Semachos 1) says 'a Goses is like a living person in every way. He inherits, bequeaths, obligates (his brother's widow) to do Yibum (or Chalitzah) and exempts (his mother) from Yibum. Regarding what is automatic, it is as if he is alive, but not for what requires an action. In Gitin we say that if Reuven made a Shali'ach to divorce, if he was Goses, the Shali'ach does not give the Get, for mpst Gosesim die. This is when that he became Goses after sending the Get. Once he is Goses, he cannot make a Shali'ach to divorce. In Erchin, we say that a Goses can vow, be Ma'arich and be Makdish. This is a stringency, for speech to Hekdesh is like Mesirah (giving Metaltelim) to a person.

Rosh (ibid): The Rashbam (127b DH b'Nechasim) says that a father is believed about property that will come to him when he is Goses and unable to speak and give. This connotes that if he could speak, he could give. R. Yo'el asked, if so, why does it discuss a Goses? The same applies to any sick person who became mute! We check his sanity. If he is sane, he can divorce or give (Gitin 71a)! Rather, we discuss only a Goses. Even if he can speak, he cannot give. The Ri proves that he is alive in every way. The ultimate Goses is one who was slaughtered, and (if he authorizes a Get) we write and give it. If one was found cut up or hanging, and he gestured to witnesses to write a Get, they write and give it, and all the more so if he speaks and his mind is settled! Gitin 28a is a great proof. We do not give a Get sent by a Goses, because most Gosesim die. If we knew that he were alive, we would give it! If he were considered to be dead, his Shali'ach could not give it. Also, it connotes that his Shali'ach may not give it, but he himself could give it directly to his wife, just like an old person, which was taught with a Goses. R. Yo'el rejected the proof from Erchin, for speech to Hekdesh is like Mesirah to a person. This is wrong. If a Goses cannot give, also his Mesirah to a person is invalid! It is not difficult for the Rashbam why we say that "Yakir" teaches about property that he gets when he is Goses. If he merely became mute, he can give it when he recovers! Rather, he became Goses and mute, and he will not recover. Also, it is common for people to become Goses before death, but not to be slaughtered or become mute.

Ran (Gitin 34a DH ul'Inyan): R. Yo'el explains that when a man became Goses after sending a Get, we do not assume 'surely he recovered, and therefore we may give it.' This is because most Gosesim die. The Ri says that a Goses is considered alive in every way as long as he can speak and his mind is settled. One who was slaughtered is even worse than a Goses, for he cannot recover, and he can divorce. We discuss property that he gets when he is Goses, for most Gosesim cannot talk. If he can talk, he can give it away.

Poskim

Shulchan Aruch (CM 250:6): The gift of a Goses is a gift.

Rashba (2:327, cited in R. Akiva Eiger and Beis Yosef 257:1): Likewise, one can acquire for a Goses. Therefore, if one says 'my property is to you with (i.e. right before) your death', he acquires.

Question (Machaneh Efrayim, Hilchos Zechiyah 16): We say that a Goses can give only if he can speak and has a sound mind at the time. Likewise, one can receive just before his death only if he could speak and had a sound mind the moment before death, which is rare!

Shulchan Aruch (EH 141:68): If Reuven made a Shali'ach to divorce, and he was Goses when the Shali'ach left him, he should not give it, for most Gosesim die. If he gave it to her she is Safek divorced.

Beis Yosef (EH Sof Siman 121 DH Mihu): The Mordechai, Semag and Semak connote that that a Goses can divorce only if he can speak. I disagree. Since he is considered to be alive, he is like a Shechiv Mera who became mute. These three Poskim said so because they saw the Ri say 'he can speak.' The Ri (and Ran and Rashba) said so only regarding a gift, but he can divorce even if he cannot speak. They bring a proof from one who was slaughtered and gestured to write a Get. The same applies to a Goses due to illness. Also, a Tosefta (Gitin 5:1) says that if one authorized a Get and fell off the roof, we may write and give it as long as he has a Neshamah. It does not depend on ability to speak! Also Gitin 28a connotes that if he were alive, we would give the Get without knowing whether or not he can speak. Tosfos (Kidushin 78b DH Lo) brings these proofs that he can divorce through gesturing, and concludes that if he cannot speak, he cannot give a gift. However, Gitin 71a equates a gift to a Get! Rather, he can give a gift even if he cannot speak. Tosfos means that if he cannot speak, presumably there is no time to test him if he wants to give a gift, or his mind is not settled, so he cannot give a gift. R. Yerucham explicitly says that his gift is valid even if he cannot talk.

Beis Shmuel (105): Only a Goses who can talk can divorce. If he cannot speak now, even though he could speak when he gave the Get to the Shali'ach, we are concerned that he lost sanity, for a Goses must be checked. However, we could say that if he could speak and was sound-minded when he gave the Get, and later he became mute, he need not be checked, since he was Goses and his mind was settled.