I, and many others in my building, store my succa in the building’s underground shelter. When I was dismantling my succa this year, I noticed that the sechach that I used was not the one I had originally bought. The difference was slight and one could easily overlook the discrepancy but I clearly remember that this is not what I bought. I asked all the neighbors and no one has sechach which even resembles the sechach I used this year. Apparently, it belonged to a neighbor who no longer lives in the building and we exchanged sechach a few years ago. I have two questions. First, about the past: Did I fulfill the mitzvah of succa or is there a problem because one does not fulfill the mitzvah of sitting in the succa if one sits in a stolen succa? My second question concerns the future: May I continue using the sechach?
Concerning the past, you have nothing to be concerned about. Even if we assume (as we will discuss later) that the sechach has the status of stolen goods, you fulfilled the mitzvah. While it is true that the Torah states (see Succa 27B where this law is derived from a pasuk) that one does not fulfill the mitzvah if he sits in a stolen succa, and according to Torah law one who steals sechach would have to remove the sechach and return it to its owner, the Rabbonon instituted a leniency (which they are able to do because they can render a person’s property ownerless). The Gemara (Succa 31A) rules that if one stole wood and used it as his sechach he is not required to remove the sechach during Succos. After Succos when the succa is dismantled the thief is required to return the sechach. However during Succos the Rabbonon said that the thief does not need to dismantle his succa and, as long as he is willing to pay for the sechach, he may leave his succa intact and he even may make a brocho when sitting in the succa (Mishna Beruro 637, 15). Therefore, even if the sechach has the status of stolen property you fulfilled the mitzvah of succa and it was okay for you to make a brocho.
Furthermore, many would not classify the sechach as stolen property. One is the Ketsos (25, 1) who proves that anyone who, due to a mistake took someone else’s property, is not considered a thief. Even if the reason the person took the object is because he thought that according to the law it is really his (but this was not the case), the Ketsos maintains that he does not have the status of a thief and the object that he took remains the property of its true owner.
The position of the Ketsos is controversial and many poskim disagree, However, your situation is much better because there is a second major opinion that the sechach is not considered stolen property. This is the Machane Efraim (Gezeilo 7) who proves that if one did not intend to take another person’s object and used something because he thought it was his, he did not commit theft. In order to be considered an act of theft one must at least intend to take another person’s possession. Unlike the Ketsos, according to the Machane Efraim it is theft even if the action was based on a mistake, but you never wanted to take someone else’s sechach.
Since you thought the sechach was yours, according to the Machane Efraim you never stole the sechach. It is true that the sechach may not have been yours but that is not a problem because, in contrast with lulav on the first day of Succos which must be yours, a succa does not have to belong to you (OC 637, 2). As long as it is not stolen, one can fulfill the mitzvah even by sitting in another person’s succa.
Thus, we determined that you fulfilled the mitzvah of sitting in the Succa all these years and we must only determine what to do now.
Since your original sechach is no longer in the shelter we can assume that it was taken by the owner of the sechach that you have been using. Since you do not know the owner’s identity we have to consider two possibilities.
One possibility is that the one who took your sechach is still unaware that he exchanged sechach with you. If that is the case, then the real owner never legally abandoned hope of recovering his own sechach since we follow the opinion of Abaye (BM 21B) that yi’ush (abandoning hope that his object will be recovered) is only legally effective if the owner is aware that he lost his object. Thus, if the one who exchanged sechach is unaware of the exchange you certainly cannot take ownership of his object.
However, since the owner of your sechach is unaware of the exchange we can assume that he is using your sechach. In this case Rav Eliashev (cited in Mishpat Ho’aveido 260, ST 169) ruled that you may use his sechach. His rationale is that since if he is using your sechach he owes you money for using your sechach. We assume that in lieu of payment for his use of your sechach he would prefer that you use his sechach in order to avoid indebtedness. Therefore, if he is unaware of the exchange you would be allowed to use the sechach since that is his preference. It is not yours but, as we mentioned before, one does not need to own the succa in which he sits.
The other possibility is that he is aware of the exchange. In this case, we cannot apply the argument of Rav Eliashev since we cannot assume that the one who took your sechach is using it. However, if this is the case we can assume that he has abandoned hope of ever recovering his own sechach, i.e. yi’ush, since so much time has elapsed since the exchange transpired. Perhaps you may even acquire ownership of his sechach. However, it is possible that his yi’ush will not enable you to keep his sechach because the Gemara (BM 21B) rules that one only acquires ownership of a lost object if he took possession of it after the owner abandoned hope. Since you probably found it before that time it could be that yi’ush will not enable you to take possession.
However, it is possible that in your case you can acquire ownership of the sechach even though you took it before its owner abandoned hope. In order to decide this issue we must understand the reason that one cannot acquire ownership of an object that he took before the owner abandoned hope.
The Rishonim have two approaches to explain this. The Ramban (BM 26B) explains that the reason is because yi’ush is only effective on objects that are no longer situated on their owner’s property. If a person gives up hope of finding his object but that object actually was situated in his own property, then yi’ush does not take effect. Furthermore, he states that when one picks up a lost object, since the Torah gives the finder the status of a shomeir, his property is dedicated to the loser’s object and it is as if the loser’s object is still sitting on its owner’s property. Therefore, yi’ush does not take effect.
There are many difficulties with understanding the Ramban’s approach and the Acharonim suggest various interpretations of the Ramban in order to avoid these difficulties. (Many difficulties are raised by the Ketsos 259, 1.)
According to some of the explanations, if the one on whose property it sat did not realize that the object was lost, like in your situation, yi’ush is effective. For example, the Nesivos (259, 1) says that only if the lost object is being watched for the owner is yi’ush not effective. In your situation you did not watch it for him so yi’ush should be effective.
Similarly, the Ohr Someach (R. Meir Simcha BM 26B) writes that the Ramban only understands that yi’ush is ineffective if the owner gave up hope because he had a mistaken impression that his object was lost, when it was really being watched for him by the finder. Since you were unaware that you had someone else’s property, it seems that yi’ush is effective because it just sat in your property but you were not safeguarding it on behalf of the owner.
The other approach to explain why yi’ush is ineffective if it took place before the owner realized that he lost anything is given by Tosafos (BK 66A). They say the reason that yi’ush is ineffective is because the finder is commanded by the Torah (hosheiv teshiveim) to return the lost object, as soon as he finds it. If he finds it before the loser gave up hope, then giving up hope does not free the finder from his obligation. According to this approach, it seems that if the loser gave up hope before you noticed that it did not belong to you, yi’ush would be effective since you were not commanded at that time to return the object since you were unaware that it did not belong to you at the time of the yi’ush. Similarly, the Imrei Moshe (37, 1) writes that if a lost object fell into a person’s property but the owner was unaware of that, he is not commanded to return the lost object.
Therefore, there are many reasons to allow you to keep the sechach.
Furthermore, even if you are not able to acquire the sechach as your own, you could still keep using the sechach. When one finds an object that is available for purchase and the owner cannot be located, the finder may evaluate the value of the lost object and record that, as well as the identifying features, on a document that is kept in a safe place and then he may use the lost object. (See Hashovas Aveido Kehalocho (6, 1) in the name of the major contemporary poskim.) The only difference between this approach and the previous one is that according to this approach if the true owner is discovered and comes to you for his sechach you will have to pay him for his sechach. Of course, it is possible that the cost will be offset by the value of your sechach. However, in any case you may keep using the sechach.
In conclusion: You may certainly keep using the sechach. You should write down the estimated value of the sechach you found and its identifying features. If you ever discover the identity of the true owner there will be an issue if you owe him money or he owes you money after considering what happened with your sechach and its value.