Kinyan HaGuf L'zman

The Ktzos HaChoshen in Simanim 241:4, 257:3, 346:5 discusses the issue of "kinyan haguf l'zman". We generally know of two types of kinyanim on an object. First, a person can own something straightaway. This is a kinyan haguf. It implies full ownership of the object. The second type of ownership is what we call a kinyan peiros. A kinyan peiros means that you don't actually own the object, but you have the right to use it. For example, a person might lease a field in order to work it and keep the produce. He doesn't actually own the field, he has only purchased the right to use the field.

The Ktzos (241:4) discusses the halacha that one is allowed to be yotzei the mitzvah of lulav and esrog with a matanah al m'nas l'hachzir. This halacha states that if someone gives me his esrog on condition that I return it to him after, it is considered good enough ownership as far as being yotzei the mitzvah. The Ktzos quotes a Ritva (1st perek of kiddushin) and a Rosh (in Perek Lulav HaGazul) who both say that the only way that this can work is if the person takes that esrog to fulfill the mitzvah, and is then "re-makneh" the esrog back to the original owner. However, if the original owner says, "I am giving you this esrog and it will automatically go back to me when you finish", both the ritva and the rosh say that this is basically a borrowed esrog and would not be a sufficient kinyan to be yotzei the mitzvah. (We are speaking now about the first day of sukkos when a borrowed esrog is not good.)

The Ktzos disputes these rishonim based on a gemara in Baba Basra 137a that discusses giving an esrog to someone "v'acharecha liploni". The gemara implies that even though the esrog will automatically leave the first guys reshus and go to the next guys, it is still a good enough kinyan to be yotzei.

Based on this the Ktzos is mechadesh the idea of kinyan haguf lizman. He says it is possible to have a kinyan for only a temporary time period and yet the kinyan is still considered to be full ownership. Even though it seems like only a kinyan peiros because you have it only temporarily, halachically that is not the case.

Update 1/14/2008: After looking into the Ktzos a little more I have discovered a few things. First, the Rashbam in the gemara in 137a seems to learn that one can be yotzei daled minim even with a kinyan peiros in the case of acharecha l'ploni. The reason is that if the entire purpose of the kinyan is only to be yotzei daled minim, even kinyan peiros is sufficient. However, the Rashba there is mashma somewhat like the ktzos that the nature of the kinyan in that case is actually more than a regular kinyan peiros, along the lines of the ktzos' chiddush of kinyan haguf l'zman. There is also a Kobetz Shiurim on the sugya that gets into these issues. I also saw brought from the Chazon Ish (Even HaEzer 74:1) that he disagreed with the Ktzos' chiddush of kinyan haguf l'zman, and held that, by defintion, if you only own something temporarily it is a kinyan peiros.

This of course is the pashtus, as this is the definition of kinyan peiros in the first place. Inventing a new concept of kinyan haguf l'zman is a big chiddush in that it undoes what are the already more logical categorizations of kinyanim that already exist.