Shenui and Yayush TB Baba Kama 65-67

Dappim TB Baba Kama 65-67 discuss two basic topics in Jewish law. The first is when a thief acquires ownership of the stolen object. The general agreement is when a change  (שִׁינּוּי) happens to that object, the thief now owns it. There is a discussion whether there’s a difference when there is an actual change (שִׁינּוּי מַעֲשֶׂה) in the object or just the name changes (שִׁינּוּי הַשֵּׁם). Everybody agrees that the thief has to make restitution to his victim even though he gets to keep the stolen object. The stolen value is calculated at the time the animal or item was stolen which includes the kefel fine or double the value of the stolen object. The penalty of four or five times the worth of the animal is calculated at the time of judgment. The Gemara sees no difference between actual change (שִׁינּוּי מַעֲשֶׂה) and a name change (שִׁינּוּי הַשֵּׁם). Nevertheless, Tosefot ד"ה שִׁינּוּי הַשֵּׁם  כְּשִׁינּוּי מַעֲשֶׂה דָּמֵ disagree and say that a name change by itself is insufficient when comes to a stolen object. For the thief to acquire the stolen object when the name changes, there has to be either be an actual change or the owner has to despair (יֵאוּשׁ) of ever retrieving the stolen object.

The second topic is when does the despairing of the original  owner (yayush  (יֵאוּשׁ) allows somebody to acquire the object. Everybody agrees concerning a lost object, the finder acquires it when the original owner despairs of ever finding it again yayush (יֵאוּשׁ) because the finder acquired it in a permissible way. However, there is a disagreement whether a thief acquires the stolen object because of yayush.

In the latter case there are three points of view. 1, Deoraita, according to Torah law, yes the thief acquires the stolen object because of yayush. 2, Derabanan, according to the rabbis decree, the thief acquires the stolen object. 3, Rav Yosef, Rav Ulla, and Rava all agree that the thief never acquires the stolen object because of yayush.

Tosefot ד"ה אָמַר עוּלָּא cites the Gemara later in our massekhet daf 114a where Ulla seemingly contradicts himself and holds the position that the thief acquires the stolen object because of yayush.  Rebbeinu Tam finds a qualitative difference between the two sugiyot. Generally speaking Rav Ulla holds that yayush is effective for the acquisition; however, the Gemara on daf 67 is speaking about a special case concerning sacrifices. May a thief offer up an animal that he has stolen as a sacrifice in the Temple? Rav Ulla forbids this sacrifice according to Rebbeinu Tam because one is forbidden to do a mitzvah whose origin is a sin (מצווה הבאה בעבירה). Because the animal was stolen which obviously is a sin, this animal cannot be used for a mitzvah, as a sacrifice on behalf of the thief.