Gittin 55: Stolen Chatas

When one who lost an item or was a victim of theft gives up hope of ever recovering it, this is termed Yi’ush. According to all opinions, a finder/thief acquires the item when Yi’ush is combined with a Shinuy. A Shinuy is a change of status, be it physical (Shinuy ha’Guf, such as grinding wheat into flour) or otherwise (such as a Shinuy ha’Shem, when the item is given a new designation – see Sukah 30a). Our Gemara records a disagreement over Yi’ush without a Shinuy (Yi’ush Kedi – Yi’ush alone). Ula maintains that Yi’ush on its own does not suffice for the current holder to acquire an item, and therefore the Chatas that had been stolen (before it was designated as such) does not belong to he who wishes to offer it. Therefore, it is invalid mid’Oraisa. R’ Yehudah maintains that Yi’ush Kedi is Koneh, and therefore the animal is his. Consequently, when designated a Chatas it is Mechaperes for him mid’Oraisa.