1) HOW MANY WITNESSES ARE NEEDED FOR A DECLARATION OF HEFKER
QUESTION: The Gemara quotes Rebbi Yehoshua ben Levi who states that mid'Oraisa an item can be made Hefker in front of just one person, but the Rabanan enacted that it be made Hefker in front of three people.
The simple reading of the Gemara indicates that mid'Rabanan, Hefker must be made in front of three people, and mid'Oraisa an item becomes Hefker if there is at least one person aware of it. However, this seems to contradict the Gemara in Shabbos (18b). The Gemara there quotes the opinion of Beis Shamai that one is prohibited to have work done with his utensils on Shabbos. However, when people see a person's lamp burning on Shabbos, they assume that the owner made his lamp Hefker before Shabbos even though no one actually witnessed the Hefker. Why is the object assumed to be Hefker? Although the requirement for three people is only mid'Rabanan and the Rabanan permitted a person to make an item Hefker without three people when he has no choice, he still needs at least one person for the Hefker to take effect mid'Oraisa!
ANSWERS:
(a) The RASH (quoted by the Piskei ha'Rosh) proves from the Gemara in Shabbos that the Gemara here does not mean that there is a requirement that Hefker be made in front of one person. Even if nobody is present when one makes his item Hefker, the item becomes Hefker mid'Oraisa.
(b) TOSFOS in Bava Metzia (30b, DH Afkera) explains that witnesses are required to assure that the owner genuinely intends to make the item Hefker. In a case in which his failure to make an item Hefker will result in a transgression of a prohibition, we may assume beyond a doubt ("Anan Sahadei") that he has absolute intention to make the item Hefker and there is no need for witnesses. Hence, in the case in Shabbos, where the owner of the lamp will desecrate Shabbos according to Beis Shamai if he does not make the lamp Hefker, we may assume that he made it Hefker with absolute intention.
(c) TOSFOS there also says that Rebbi Yehoshua ben Levi requires the Hefker to be made in front of others only with regard to making produce exempt from Ma'aser. With regard to other laws, the declaration of Hefker takes effect even when no one else witnesses it.
(d) The MORDECHAI (quoted by the VILNA GA'ON OC 246) answers that witnesses are needed only when one declares as Hefker an item which is not usually made Hefker. Since everyone makes their lamps Hefker before Shabbos (according to Beis Shamai) there is no need for witnesses.
HALACHAH: The SHULCHAN ARUCH (CM 273:7) quotes the RAMBAM'S opinion that mid'Oraisa a declaration of Hefker must be made in front of one person, and mid'Rabanan in front of three. The REMA quotes the ROSH who rules that if one made a declaration of Hefker in front of no one, the Hefker still takes effect. (See VILNA GA'ON ad loc.)
However, the Shulchan Aruch seems to contradict his ruling. In Hilchos Shabbos (OC 246:3), the Shulchan Aruch rules that if one rented his animal to a Nochri on the condition that the Nochri return it before Shabbos, and the Nochri kept it in his possession during Shabbos, the owner may declare the animal Hefker in front of no witnesses. (The Rema says that it is preferable to declare it Hefker in front of three witnesses.)
QUESTION: Why does the Shulchan Aruch rule (in Hilchos Shabbos) that one may make his animal Hefker in front of no witnesses, while he rules (in Choshen Mishpat) that one must make an item Hefker in front of at least one person in order for the Hefker to take effect mid'Oraisa?
Moreover, the Rema (in Choshen Mishpat) cites the Rosh who says that the Hefker takes effect even when there are no witnesses. Why, then, in Hilchos Shabbos does the Rema mention that one should make the animal Hefker in front of three people?
ANSWERS:
(a) The SHA'AR HA'TZIYUN (OC 246:18) quotes the TOSFOS SHABBOS who answers that in Hilchos Shabbos the Shulchan Aruch is discussing a case in which no one else is present to serve as a witness to the owner's declaration of Hefker. The Shulchan Aruch writes that since the owner has no other choice, he should be Mafkir his animal by himself and rely on the opinions that such a declaration of Hefker is valid.
Alternatively, perhaps the Shulchan Aruch in Hilchos Shabbos relies on the answer of Tosfos in Bava Metzia who writes that there is no need for witnesses in a situation where the owner wants to prevent himself from transgressing an Isur.
When the Rema in Hilchos Shabbos writes that one should be stringent and be Mafkir his animal in front of three people, he follows the view of the Mordechai (mentioned above). Since people usually do not make their animals Hefker, one who wants to make his animal Hefker must do so in front of three witnesses. (The MISHNAH BERURAH there writes that when possible one should be Mafkir his animal in front of at least one person.)