The Gemara refutes the proof and says that in that case, there is both
Yi'ush and Shinuy ha'Shem, since the change from Chulin to Hekdesh, or from
Tevel to Terumah, is considered a Shinuy, and therefore the thief is Koneh
the item. Yi'ush alone, though, might not be enough to be Koneh the item.
The Gemara's answer is difficult to understand. We know that in a pile of
fruit, there are two parts -- the part that is Terumah, and the rest of the
pile that is Chulin. The part that is Terumah indeed had a Shinuy ha'Shem
when it was separated and turned from Tevel into Terumah, but the part that
is Chulin did not, apparently, have any Shinuy ha'Shem! It merely changed
from being Asur (Tevel) to being Mutar (Chulin), but it had no Shinuy
ha'Shem. Thus, the thief was not Koneh the rest of the pile; he was Koneh
only the Terumah. But if that is the case, then how is his separation of
Terumah a valid Terumah? He is separating Terumah from his own fruits (that
he was Koneh through Yi'ush and Shinuy ha'Shem, if we apply the principle of
"Ba'in k'Achas") on behalf of someone else's fruits (the Chulin, which had
no Shinuy ha'Shem and which he was not Koneh)!
(a) The OR SAME'ACH (Hilchos Gezeilah 5:4) answers simply that the Halachah
is that one who separates Terumah from his own fruits on behalf of someone
else's fruits does not need the consent of the other owner.
There are several questions on his answer, though. First, the reason why one
is able to separate Terumah from his own fruits on behalf of someone else's
is because of the principle, "Zachin l'Adam she'Lo b'Fanav." Here, however,
the concept of "Zechiyah" is not applicable, because the owner would have
preferred that the thief *not* take Terumah, because if the Terumah would
not take effect, then the thief would not be Koneh it. If the thief would be
Koneh the Terumah, it would be a "Chav" (a detriment or loss) to the owner,
and thus his separating of Terumah should not take effect! (See CHASON ISH,
Bava Kama 17:17; ACHI'EZER 3:55:3; RAV SHLOMO ZALMAN AUERBACH zt'l in
MA'ADANEI ERETZ, Terumos 4:11:2.)
Second, many Rishonim maintain that "Zechiyah" works through Shelichus, such
that, in our case, either we assume that the original owner would have made
the thief a Shali'ach to separate Terumah for him, or that the Torah makes
him a Shali'ach. However, Shelichus works only when the owner is able to do
the act that he is appointing his Shali'ach to do. Here, the owner is unable
to separate Terumah because the fruits are not in his domain, and thus the
thief should also not be able to separate Terumah. (The Or Same'ach himself
asks this question, as does the Achi'ezer 2:37:3.)
Third, the KETZOS HA'CHOSHEN (#243 and elsewhere) teaches that "Zechiyah"
works only to be Zocheh an item *to* a person (i.e. to put an item into his
possession), but not to be Zocheh an item *from* a person (i.e. to remove an
item from his possession). Here, the principle of "Zechiyah" cannot work to
enable the thief to take Terumah from his fruits for the fruits of someone
else, since he is not giving anything to the owner of the fruits. He is
merely attempting to use his own property to enable the owner to do a
Mitzvah, and for this, "Zechiyah" does not work.
These three questions on the answer of the Or Same'ach can be answered based
on what RABEINU CHAIM HA'LEVI SOLOVEITCHIK, the Brisker Rav, writes (in
Chidushei ha'Grach, "stencil" version, #244). Although in all other cases
where one person separates Terumah from his own fruits on behalf of someone
else's fruits, the Terumah takes effect through the mechanism of "Zachin
l'Adam she'Lo b'Fanav," in the case of our Gemara it works differently.
Normally, the only reason "Zechiyah" is necessary is because one must
separate Terumah from the pile of fruits that are Tevel, for which the
Terumah is being separated, and not from someone else's pile of fruits on
behalf of this pile (as derived from the verse, "Es Mikdasho Mimenu"
Bamidbar 18:29). However, to separate Terumah from one person's pile for him
is not a Zechus, but a Chov, and therefore one is only able to separate from
his own pile on behalf of his friend's pile, for then the principle of
"Zachin l'Adam" makes it as if the fruits of Terumah belong to his friend,
and the Halachah of "Es Mikdasho Mimenu" (Bamidbar 18:29) is fulfilled.
In our case, though, the thief is able to separate Terumah from this pile
itself (that he stole), since he is Koneh the Terumah through Yi'ush and
Shinuy ha'Shem, and thus the requirement of "Es Mikdasho Mimenu" is
fulfilled, and even without the principle of "Zachin l'Adam," the Terumah
takes effect.
(b) RAV SHIMON SHKOP (Chidushim 35:1) proves from this Gemara that the
change from "Tevel" to "Chulin" is also considered a Shinuy ha'Shem.
Consequently, the thief is certainly able to make the Terumah take effect,
because he is also Koneh the Chulin part of the fruits.
The ACHI'EZER rejects this answer and infers from the wording of the Gemara,
"Originally it was Tevel, and now it is *Terumah*," that only the change
from Tevel to *Terumah* is considered a Shinuy ha'Shem, and not the change
from Tevel to Chulin.
(c) The ACHI'EZER instead suggests that the Tosefta is discussing a case in
which the thief separated Terumah from the fruits of the original owner, on
behalf of the thief's own fruits (and not on behalf of the owner's fruits).
The Terumah takes effect because he is Koneh those fruits with Shinuy
ha'Shem. (See also ONEG YOM TOV 108.)
The GEDULEI SHMUEL writes that the Or Same'ach did not accept this answer
because the Tosefta says that the Terumah of the thief is valid, without
specifying that it is valid only when he separates Terumah from the original
owner's fruits on behalf of his own fruits.