Gemara

Yakov's son Levi used to steal flax. Yakov forbade his property to Levi son. Friends suggested that perhaps Levi's son will be a Chacham!

Shimon: Levi should acquire the property on condition to give it to his son if his son will be a Chacham.

Question: Does this work?

Answer #1 (Chachamim of Pumbadisa): No. One cannot acquire on condition to give to someone else.

Answer #2 (Rav Nachman): It works. In Kinyan Sudar (acquisition through giving a garment), one takes the garment only in order to give something else!

Objection #1 (Rav Ashi): Perhaps the one who takes the garment can keep it (and Rav Nachman has no proof)!

Objection #2 (Rav Ashi): One who does Kinyan Sudar takes the garment in order to give now to someone else;

In the above case, Levi acquires only when his son will be a Chacham. By then, the garment has already been returned!

Kidushin 6b (Rava): If one said 'here is money on condition that you return it to me', this is not a valid Kinyan Kesef (to buy land), it cannot make Kidushin, and it cannot redeem a firstborn son. Such a gift fulfills the Mitzvah of giving Terumah.

Objections: If a gift on condition to return it is considered a gift, it should work in all the cases! If it is not a gift, it should not help for Terumah, either! Also, Rava taught that one fulfills the Mitzvah of Esrog through such a gift!

(Rav Ashi): Rather, such a gift works in all cases, except for Kidushin, because it resembles Chalipin (exchange), which cannot make Kidushin.

Kesuvos 82a (Rav Dimi citing R. Yochanan): If Reuven told Shimon 'do Meshichah on this cow (take it to your premises), but it is not yours until 30 days from now', 30 days later he acquires it, even if it is in a swamp.

Contradiction (Ravin citing R. Yochanan): The cow is not acquired 30 days later.

Answer: Rav Dimi discusses when he said 'acquire from now.' In Ravin's case, he did not say this.

86b (Rav Nachman): If Reuven told Shimon 'be Moshech this cow, but it is not yours until 30 days', he acquires it then, even if it is in a swamp.

Rishonim

The Rif and Rosh (5:5) bring our Gemara.

Rambam (Hilchos Nedarim 5:7): If Yakov forbade his property to Levi, and said 'if his son will be a Chacham, Levi should acquire my property in order to give it to his son, this is permitted.

Rosh: The Rambam says that the Halachah follows Rav Nachman, who says that Chalipin is Kinyan in order to be Makneh (transfer ownership), i.e. a gift on condition to return it. Rav Ashi said 'perhaps the one who takes the garment can keep it'. This is a mere Dichuy; he himself (Kidushin 6b) said that a gift on condition to return it always works, except for Kidushin, in which we decree lest people say that Chalipin makes Kidushin. It seems that Chalipin cannot be Makneh to the grandson through Levi, for the garment was returned beforehand. Surely Chalipin to take effect after 30 days works only if he said 'from now'. If not, it is invalid, for the garment was already returned.

Ran (Nedarim 48b DH Amrei): Yakov's gift to Levi to be Makneh to Levi's son is unlike a gift on condition to return it. There, the recipient may use it while he has it. Here, Levi received no rights in the property at all. Rav Nachman says that it works, just like in Chalipin one takes the garment merely for the sake of the Kinyan. Rav Ashi said that perhaps this is not true. And even if it is true, here the Kinyan to Levi is Batel before Levi's son receives. Rav Nachman agrees that Meshichah to acquire after 30 days does not acquire if the cow is in the swamp after 30 days. He thought that here, since Yakov did not specify that Levi not acquire until he has a son who is a Chacham, it is as if he said 'from now'. Rav Ashi rejects this. Since Yakov wanted to give only to the grandson, he did not want Levi to acquire beforehand.

Question (Ran 27b DH v'Hu): The Gemara says that Asmachta acquires in a distinguished Beis Din. Why is this necessary? The Gemara (Bava Metzi'a 66b) says that there is no problem of Asmachta when they said 'from now'. Every Chalipin must be 'from now', for otherwise it is invalid, for the garment was already returned!

Answer (Ran): R. Tam says that 'from now' avoids Asmachta only in a case like in Bava Metzi'a (a field was given for collateral, on condition that the lender can keep it if the loan is not paid in three years). If the property was not given over, Asmachta still applies. I say that a distinguished Beis Din merely avoids the need to say 'from now'. It is as if he said it, for people do not jest in Beis Din.

Magid Mishneh (Hilchos Mechirah 11:13): The Rambam says that Asmachta applies to Chalipin. It seems that he holds that Chalipin works without 'from now'.

Poskim

Shulchan Aruch (CM 195:5): Some say that Chalipin works only if the sold or given object is acquired immediately, but if the buyer said 'acquire this garment and be Makneh (transfer ownership of) your item to me after 30 days', he does not acquire, for at the time he should acquire, the garment was returned to the buyer. If he said 'acquire (this garment) on condition to be Makneh to me from now and after 30 days', he acquires.

Beis Yosef (DH v'Chosvu ha'Tosfos): Tosfos (Kidushin 63a DH Chegon) asks, according to R. Yochanan, how we acquire anything for a later time, such as Shiduchim (commitments to get married) or other Tana'im. R. Yochanan holds that saying 'from now' does not help if one retracted, or regarding Chalipin, for the garment already returned to the owner. Rabbeinu Meir answered that perhaps 'Al Menas' (on condition) helps even according to R. Yochanan. It is a Tanai, not a deficiency in the Kinyan. Therefore, it is good to say 'Al Menas from now.' It is not clear why 'from now' is needed. Perhaps it is to publicize that it is from now. Talmidei ha'Rashba say that if Chalipin is not to acquire, rather, merely to avoid Asmachta, it helps even for later if it was in a distinguished Beis Din.

Beis Yosef (DH u'Maharik): The Maharik says that when Chalipin is done, one need not write 'from now'. Others disagree.

Mordechai (Kidushin 525,526): Kinyan Kesef does not need 'from now', for if the Kinyan is Batel the money must be returned. Chalipin is like Kinyan Kesef; it does not require 'from now'.

Note: Returning the garment does not depend on Bitul of the Chalipin! Perhaps Chalipin is a form of Kinyan Kesef, and therefore the same laws apply. Alternatively, here 'Chalipin' refers only to a swap (e.g. a donkey for a cow), but not to Kinyan Sudar. However, the Shach (CM 191:5) understands that the Mordechai discusses Kinyan Sudar.

Gra (191:10): Regarding Chalipin, we must say that Rav and R. Yochanan agree with Shmuel (that it helps to say 'from now').

Rema: Stam, we say that it is as if he said 'from now' in a way that works. People do not do things for naught.