1) LIVING IN PROXIMITY OF A NOCHRI
QUESTION: The Mishnah (61b) says that the domicile of a Nochri in a Chatzer prohibits the Jewish residents from carrying in the Chatzer on Shabbos. The Nochri may not be included in the Eruv, nor may he be Mevatel his Reshus to the Jewish residents. The only way the Jews in the Chatzer can permit carrying there is by renting from the Nochri his rights to the Chatzer. This, however, might make it difficult to permit carrying in the Chatzer, because the Nochri may not want to rent out his rights to the Jews.
The Gemara says that the Rabanan created an obstacle to obtaining permission to carry a Chatzer shared with a Nochri in order to deter Jews from living so close to a Nochri, lest they learn from his ways and begin to act like him.
If the Rabanan did not want Jews living in the same Chatzer as a Nochri, then instead of decreeing that an Eruv cannot be made in a Chatzer without renting the Nochri's rights to the Chatzer, they should have decreed that it is forbidden to live near a Nochri! Why did they enact such an indirect deterrent when they could have made it outright forbidden for Jews to live near Nochrim?
ANSWER: The GA'ON YAKOV explains that the Rabanan chose not to forbid a Jew from living near a Nochri, because sometimes one has no choice about where he lives. (He may have inherited a house or received it as a gift.) Therefore, the Rabanan did not forbid a Jew from living near a Nochri.
Instead, the Rabanan decreed that one who lives in the same Chatzer as a Nochri must rent rights from the Nochri in order to permit carrying in the Chatzer on Shabbos. Such a Gezeirah may deter one who does have a choice where to live from living in the same Chatzer as the Nochri.
2) A NOCHRI WHO IS NOT HOME
QUESTION: The Gemara asks that there is an apparent contradiction between the Beraisa (62a) and the Mishnah (61b). The Beraisa states that a Nochri's residence in a Chatzer does not forbid the Jews who live there from carrying. The Mishnah, however, states that a Nochri's residence does forbid the Jews in the Chatzer from carrying there.
The Gemara answers that the Beraisa refers to a Nochri who is not home. The law is that when a Jew who has not joined in the Eruv is not home, his absence is irrelevant and his lack of participation forbids the other residents of the Chatzer from carrying. Even though "Dirah b'Lo Ba'alim Lo Shmah Dirah" (when the owner of a house is not present, it is as if his entire house is not there), the Rabanan decreed that we consider the Chatzer as though the owner is present. A Nochri, however, should not prohibit his Jewish neighbors from carrying in the courtyard even when he is present (if not for the desire of the Rabanan to deter Jews from living near a Nochri so that they not learn to emulate his ways). Therefore, when the Nochri is not home the Jews may carry in the Chatzer.
Why does the Gemara assume that a Jew who is not home forbids the other residents of the Chatzer from carrying only because of a Gezeirah ("Dirah b'Lo Ba'alim Lo Shmah Dirah")? The Gemara could have said simply that one who is absent from his home is considered as though he is residing in his home ("Dirah b'Lo Ba'alim Shmah Dirah"). Consequently, a Jew forbids his neighbors from carrying even when he is not home, while a Nochri (whose presence forbids Jews from carrying only because of the decree to deter them from living near him in the first place) does not!
ANSWER: The Gemara does not give this answer because if, when a person is not home, it is considered as though he is still living there ("Dirah b'Lo Ba'alim"), then there would be absolutely no basis to differentiate between one who is home and one who is not home, even if he is a Nochri. If his ownership of the home forbids the residents of the Chatzer from carrying when he is present, then when he is not present his ownership of the home also forbids them from carrying. (GA'ON YAKOV)