The core principle of shinui koneh is set out in the mishna: one who robs wood or wool and fashions them into vessels or garments acquires them through the change and need only pay the value at the time of the robbery, not return the item itself (Bava Kamma 93b:1). The Gemara there, through Abaye, clarifies that this mishna discusses a rabbinically significant change that is reversible, and that a Torah-level, irreversible change acquires all the more so.
The Gemara extends this concept beyond physical change to a change of name alone: Rav Yosef resolves a longstanding difficulty by teaching that a change in what an item is called is equivalent to a change wrought by an action, since in both cases the item's prior identity has been replaced by a new one (Bava Kamma 66b:14-15). The principle that shinui koneh exists as a dispute is also stated directly, contrasting one view that a change effects acquisition with the view that it does not (Bava Kamma 66a:2).
The Shulchan Arukh codifies the rule that once the stolen item has changed, the robber need only pay its value as of the time of the robbery, provided the change is not one that reverts to its original form — giving examples such as nailing wood into a box (reversible, no acquisition) versus smoothing and cutting wood into vessels, dyeing or carding wool, or melting coins (irreversible, acquisition) (Shulchan Arukh, Choshen Mishpat 360:5-7). The Shulchan Arukh further rules that reducing large beams into small ones does not effect acquisition, while cutting them into boards does, once their name has changed (Shulchan Arukh, Choshen Mishpat 360:9).
The Rambam likewise holds that old coins melted and reminted are not acquired, since they can revert, whereas new coins made old are acquired because they now have a new identity, and a cut-down palm tree is not acquired unless it is fashioned into beams (Mishneh Torah, Robbery and Lost Property 2:13). He similarly rules that one who breaks a stolen vessel does not acquire it through depreciation but must pay its value, leaving the broken vessel with the robber unless the owner chooses otherwise (Mishneh Torah, Robbery and Lost Property 2:15).
Later commentators probe the theoretical basis of shinui koneh itself. The Ketzot HaChoshen traces the dispute among the Rishonim over which pesukim generate the law of shinui koneh and whether it applies even to a reversible change (Ketzot HaChoshen on Shulchan Arukh, Choshen Mishpat 360:2), while the Netivot HaMishpat questions whether a change of name alone, combined with despair of recovery, can ever acquire on a Torah level, given that the verse underlying shinui seems to require an irreversible change (Netivot HaMishpat, Beurim on Shulchan Arukh, Choshen Mishpat 361:1).
Modern analysis continues to ask whether shinui koneh is itself an independent form of acquisition or merely a release from the obligation to return the item in its original form, since the item's altered form is no longer identical to what was stolen (Reshimot Shiurim on Bava Kamma 66a:1). A parallel discussion considers why despair of recovery (yeush) requires the thief's intent to acquire while shinui apparently acquires even against the thief's will (Reshimot Shiurim on Bava Kamma 66b:1), and another treatment argues that the acquisition of offspring from a stolen animal may rest not on shinui koneh at all but on a separate rabbinic entitlement, since the Rambam limits that acquisition to cases following yeush (Reshimot Shiurim on Bava Kamma 95b:14).
Rabbeinu Chaim HaLevi examines whether the thief's inability to discharge liability by returning a damaged item stems from the fact that shinui generates acquisition, or independently from the fact that the item is no longer in the form in which it was stolen, drawing on the dispute over a stolen lamb that grew into a ram (Chiddushei Rabbeinu Chaim HaLevi, Robbery and Lost Property 2:15). The Chazon Ish addresses related applications: whether shinui koneh applies to an animal that has been fattened (Chazon Ish Bava Kamma 7), and whether shinui fails to effect acquisition where the person did not intend to steal, including the case of a poor person liable for a whole animal or vessel (Chazon Ish Bava Kamma 20).
The Chatam Sofer addresses the Rambam's position that one who acquires through yeush and shinui of possession must still return the value to the owner, raising and resolving the difficulty of how the Torah's prohibition against the act can nonetheless produce a valid acquisition (Responsa Chatam Sofer, Choshen Mishpat 56:1-2).
Rav Tzvi Pesach Frank, in Har Tzvi YD 42, rules that material alteration completes an acquisition only where the item had already become one's own through a prior obligation of onesin, whereas altering an item without having first become liable for it does not effect acquisition — a distinction he draws from the case of a thief who slaughters the animal in the owner's own domain.
