I found this, from the Chicago Community Kollel. Footnote 8 does quote a heter. Ask your posek; I don't know if it is commonly accepted.
Rabbi Moshe Rosenstein
It has happened to almost everyone at some point in their lives – on the coldest Shabbos night of the year, after davening, Reuvain walks over to the coat rack to get ready to bundle up and brave the elements. As he chats with his friends, he leafs through the hanging coats, wondering if he may have left his coat on the other rack. One by one his friends find their coats and leave, bidding him a “Good Shabbos.” Finally, Reuvain is left alone in the coatroom with only one coat left on the rack. While it does indeed look nearly identical to his, he knows it is not, as his had a small tear in the back of the left pocket. Looking outside at the howling wind and whirling snow, looking around him and realizing that he is the last one left in the shul and some other Chicagoan is toasty warm in his coat, Reuvain scratches his head and wonders if it is permissible to take that one coat that was left behind “for him.”
The Halachic Background
The Gemora [Bava Basra 41a] and Shulchan Aruch [Choshen Mishpat 136:2] are clear regarding this din. “If someone’s clothing was switched in a house of mourning or a house where there was a party, he may not use the [clothing that was switched with his own].” The Shulchan Aruch is discussing a case where the switch has already taken place, and only later did the parties realize that the item they had taken is not their own. The Halacha, however, is the same if one realizes that his item was taken and another item accidentally left in its stead. He may not take the item that does not belong to him even though his item was taken by the owner of the item left behind. The reason for this prohibition is that since the real owner is not present to allow use of his item, “borrowing” (i.e. using) that item is forbidden and is considered to be gezel, stealing [sho’el shelo mida’as].1 Depending on the circumstances, the item left behind may indeed have the status of an aveidah, a lost item, and the finder may have the responsibility to see to it that it is returned to its rightful owner (hashavas aveidah). However, this in no way would permit him to use the item in the interim. The only time it is permissible to use an aveidah that one finds is if it is picked up after the true owner realizes his loss and gives up hope of finding his item. This status is referred to as “yei’ush.” The ramifications of this status will be discussed below.
The Practical Halacha
We will discuss how the poskim instruct us to deal with various different practical scenarios of switched articles of clothing.
An item is missing and there is another, similar item left in its place:
Even if one is completely certain that his item (coat, towel, hat, etc.) was taken accidentally and he is certain that the item left behind belongs to the person who took his (i.e. it is very similar and hanging in the same place his was left), under most circumstances it will not be permissible for him to take the item left behind, even for temporary use.
There is, however, an exception to this rule. If the finder can assume that enough time has passed and the true owner of the item left behind has already realized that he accidentally took the wrong item, it is permissible for the finder to take and use the item left behind.2
He must have taken the wrong item home – this is similar to his coat, but it’s not his:
Even if he already took the item home accidentally, and only then realizes that it is not his own, it is not permissible to use the item. If there is a way for him to find out whose it is, he should do so. Otherwise, the item should be treated like an aveidah and he should return it to the place he took it from, as the real owner may return to look for it there. Even after the lapse of a significant amount of time, and even if we can be sure that by now the original owner has given up finding his item (yei’ush), it will still not be permissible to use the item. Since when it was originally taken yei’ush did not yet set in, it is considered to have been “stolen” by the finder. Therefore, it is an item that “came into his hands in a prohibited manner” and may not be used.
Some poskim, however, do not consider this a permanent status. They contend that if two criteria are met, the finder may indeed use the item he took home. If both
· a very long time has passed and
· the finder knows for sure that his original (now lost) item is in the hands of the owner of the item he now has.
If these conditions are met, the poskim say, it can be assumed that the original owner has not only given up hope of finding his item, but he has also resolved himself to considering this switch permanent.3 Some add that before using the item the finder should estimate its monetary value and write in his monetary record books that should he find the actual owner he will pay him back for the item.4
There is, however, an exception to this leniency. If the switched items are exactly the same, then there is no way for the finder to ever be sure that the original owner has even realized that a switch took place. Under these circumstances, it will not be permissible for him to use the item he has found.5
A prevalent custom not to be particular about allowing use of an item
There are certain rulings found in the later poskim that should be mentioned regarding this topic. As with all issues of this nature, a shailoh should be asked if one feels that a situation has arisen that would require clarification of the Halacha.
The Aruch HaShulchan6 ruled regarding switched galoshes that since it is the norm to leave all the galoshes together at the entrance to a building, and since the prevalent practice is not to be particular about letting others take one’s own galoshes, this halacha would not apply. HaGaon Rav Moshe Feinstein zt”l, however, limited the application of this ruling only to a situation where there is a clearly defined minhag not to be particular about switching items. In a situation where there is no well-defined common practice, one may not be lenient even regarding common, everyday items.7 Rav Moshe zt”l suggests that every shul (or other public place) have a well defined policy clearly posted regarding this matter. That would, in effect, make the “minhag” of that institution clearly defined.8
Additionally, if the finder knows who the owner of the left-behind coat is, and knows that the owner would not mind allowing him to use his coat, it will be permissible. [For more on this, see Parsha Encounters for Parshas Noach, “It Takes a Thief.”]
1 See Rashbam B.B. s.v. harei zeh and Shulchan Aruch C.M. 358:5
2 Pischei Choshen vol. 1 Aveidah 4:19:45. Rav Yisroel Belsky shlit”a is also quoted as ruling this way in Halacha Berura vol 5, 12.
3 Pischei Choshen ibid. Rav Bloi shlit”a maintains that under these circumstances the switch may be viewed as an actual sale. Under these circumstances, even if the item was originally taken b’issur, it would now be permissible to use.
4 Mishpitei HaTorah vol. 3 3:17. [He does not mention the reasoning above in note 3.]
5 Pischei Choshen ibid. s.v. ela.
6 C.M. 136:2
7 Iggeros Moshe O.C. 5:9.7 regarding switched “davening jackets” in a shul.
8 It should be noted that a more encompassing leniency is to be found in the poskim. HaGaon Rav Yaakov Kaminetsky zt”l, in a seemingly novel approach to this halacha, is quoted as ruling that it is permissible for the finder to take the coat item left behind. Since the first person to take the wrong coat in effect “stole” the coat that he took, the one whose coat was taken may take the coat left behind as “payment” for the stealing of his coat. While the ruling does not include the following caveat, it would seem clear that this would only be permissible if the coat left behind is of equal or lesser value to the coat that was taken. See there for more details regarding this ruling.
Rabbi Rosenstein is a full-time member of the Kollel and is a frequent contributor to Halacha Encounters.