Before R"H a fellow blogger bemoaned the lack of attention paid to the Ketzos these days, as bnei torah spend more time delving into the brisker lomdus of the great roshei yeshivos rather than reading classics. Maybe we should devote more time in the coming year to the Ketzos, Shmaytza, and Avnei Miluim... this sukkos piece is a good place to start, as it is two parter; you get twice the lomdus for the same mareh mekomos.
There is a mitzvah to return stolen goods. If you steal a beam and use it in your home, the chachamim made a special takanah as an incentive to tshuvah and allow you to pay for the beam rather than force you to dismantle your home to return it. What if the stolen beam was used in a sukkah? The gemara says that for the duration of sukkos the beam is considered owned by the thief -- he is obligated to repay the original owner, but we do not force the dismantling of the sukkah any more than we would force the dismantling of a home. However, once sukkos is over and the sukkah is dismantled anyway, the original beam must be returned.
Yesterday we discussed whether a kinyan derabbanan has a chalos d'oraysa (parenthetically, someone asked a great kashe in the comments that is worth taking a look at). The Sha'ar haMelech suggests that this case of the stolen beam can help us resolve that issue. Min haTorah the stolen beam is not owner by the thief -- it should be returned. It is only the takanah derabbanan that allows the thief to keep it. QED: by virtue of a takanah derabbanan we have a chalos of a sukkah that is kosher min hatorah!
The Avnei Miluim (28:33) rejects this proof. There is a basic difference between a stolen lulav (for example) and a stolen sukkah (actually, stolen schach). A stolen lulav is pasul because the Torah requires ownership of the lulav as a condition of fulfilling the mitzvah; a thief is not the lulav's true owner. A stolen sukkah is pasul not because the Torah requires ownership of a sukkah -- the reason a stolen sukkah is pasul is simply because stolen goods are unacceptable for a mitzvah purpose (mitzvah haba'ah b'aveira). A kinyan derabbanan may not have a chalos d'oraysa in the sense of being "yours" from a Torah perspective, but a kinyan derabbanan is certainly sufficient to remove the label of "stolen goods" from the object. Think about it this way: if you make a kinyan derabbanan on an item without a kinyan min haTorah, whether or not the object is truly "yours", it is inconceivable that min haTorah you should be considered a thief!
The Avnei Miluim uses this same case as proof in a different controversy - stay tuned for part II.