1) THE REMOVAL OF A MAMZER'S STATUS THROUGH MARRIAGE WITH A "SHIFCHAH"
QUESTION: In the Mishnah, Rebbi Tarfon states that it is possible to remove the status of illegitimacy from the offspring of a Mamzer. When a Mamzer marries a Shifchah (a non-Jewish maidservant), the child born to them is an Eved Kena'ani. When the Eved Kena'ani is freed he becomes a full-fledged Jew without the status of a Mamzer. The Gemara concludes that Rebbi Tarfon's advice to a Mamzer is intended even l'Chatchilah; a Mamzer may marry a Shifchah even l'Chatchilah in order to remove the status of Mamzer from his offspring.
RASHI (DH O Di'eved) explains that the prohibition against marrying a Shifchah is derived from the verse, "Lo Yiheyeh Kadesh" (Devarim 23:18). A Mamzer is obligated to observe all of the prohibitions of the Torah, including prohibitions which involve marriage (such as the prohibition against marrying a Nochris, as the Gemara (68b) derives from "Lo Sischaten Bam" (Devarim 7:3)). Why does Rebbi Tarfon maintain that the prohibition of "Lo Yiheyeh Kadesh" is different? Why does he permit a Mamzer to transgress that prohibition l'Chatchilah?
ANSWER: The RASHBA here quotes RABEINU TAM (see also TOSFOS to Yevamos 79b) who answers that the prohibition against marrying a Shifchah differs from other Isurei Lav. The other prohibitions which involve marriage specifically prohibit the marriage. The prohibition against marrying a Shifchah states that being a Kadesh is prohibited. The prohibition does not prohibit the act of marriage per se with a Shifchah. Rather, it prohibits the outcome of such a marriage -- the man's status as a Kadesh. Hence, although a Mamzer is considered an ordinary Jew with regard to all of the Mitzvos, his birth came about through an act of sin and thus he lacks the element of Kedushah, holiness, which a member of the Jewish people should have. He was born through an act of "harlotry" ("Kedeishus"), an act that involved the opposite of holiness ("Kedushah"). Since he has already been blemished with an element of a "Kadesh," there is no need for him to refrain from marrying a Shifchah. The Torah prohibits a Jewish man from marrying a Shifchah in order to prevent him from losing his holiness by becoming a "Kadesh." Since the Mamzer already has that blemish, he may marry a Shifchah.
2) THE PROHIBITION AGAINST FREEING AN "EVED KENA'ANI"
QUESTION: In the Mishnah, Rebbi Tarfon states that it is possible to remove the status of illegitimacy from the offspring of a Mamzer. When a Mamzer marries a Shifchah (a non-Jewish maidservant), the child born to them is an Eved Kena'ani. When the Eved Kena'ani is freed he becomes a full-fledged Jew without the status of a Mamzer. The Gemara concludes that Rebbi Tarfon's advice to a Mamzer is intended even l'Chatchilah; a Mamzer may marry a Shifchah even l'Chatchilah in order to remove the status of Mamzer from his offspring.
Why does Rebbi Tarfon permit the Mamzer who marries the Shifchah to free his son, the Eved Kena'ani? The Torah forbids a Jewish master from freeing his Eved Kena'ani (Gitin 38b)! Even if the Mamzer is not prohibited from marrying a Shifchah (see previous Insight), he still is prohibited from freeing an Eved Kena'ani. Why does the Gemara conclude that this method of removing the status of Mamzer from his offspring is permitted l'Chatchilah?
ANSWER: The RAN in Gitin (38b) explains that the prohibition against freeing an Eved Kena'ani is part of the Isur of "Lo Sechanem" (Devarim 7:2), the prohibition against giving a gift to a Nochri. When a master frees his Eved Kena'ani, he thereby gives him a "gift" of freedom.
However, the Isur of "Lo Sechanem" does not prohibit one from giving a gift to a Nochri for one's own personal gain. Hence, in the case of Rebbi Tarfon, the master who frees the Eved (his son) does so for his own personal gain -- to remove the status of Mamzer from his family's lineage. (See MAHARSHA's comments on "Ushpezichnei d'Rebbi Simla'i," and HA'MIKNAH there.)
3) PERMITTING A MAMZER TO MARRY A "NESIN"
QUESTION: The Mishnah lists "Nesini" as one of the ten levels of lineage which ascended with Ezra to Eretz Yisrael from Bavel. The Rishonim explain that Nesinim are converts from the seven nations (specifically the Giv'onim, part of the Chivi nation) which occupied Eretz Yisrael at the time the Jewish people entered the land. The Gemara in Yevamos (76a) discusses whether or not the prohibition against marrying a member of the seven nations applies even after he converts. The conclusion of Rava there (according to some Rishonim) is that a Jew is prohibited from marrying a member of the seven nations even after that person converts. (This prohibition applies only to marrying the convert himself. A Jew is permitted to marry the convert's child born after the conversion.)
The Mishnah here states that a Mamzer is permitted to marry a Nesin. However, the prohibition against marrying a Nochri ("Lo Sischaten Bam"; see 68b) applies to a Mamzer just as it applies to every other Jew. Why may a Mamzer marry a Nesin if a Nesin is a convert from one of the seven nations?
ANSWER: The RAN differentiates between the prohibition against marrying a Nochri before he or she has converted, and the prohibition against marrying a Nochri from the seven nations after he or she has converted. The Gemara earlier (68b) teaches that the verse itself gives the reason for the prohibition of "Lo Sischaten Bam," which prohibits marriage to a Nochri: "For he will turn your son away from Me." Since the Nochri worships idols, the Torah warns that a child born to a union with a Nochri will follow the Nochri's sinful ways.
In contrast, the prohibition against marrying a Nochri from the seven nations after he has converted (as mentioned in Yevamos) is different. Since the Nochri has converted and has accepted upon himself to observe the Torah and all of the Mitzvos, there is no concern that he "will turn your son away from Me." Rather, the prohibition against marrying a convert from the seven nations is a prohibition of "Pesul Yuchsin" -- to prevent the Jewish people from mingling with the seven nations.
Since a Mamzer is a Pesul (a Jew of blemished lineage), he is not commanded to avoid marrying a Pesul. (This is similar to the logic of the RASHBA, cited above in Insights to 69:1.) He is, however, commanded to avoid a marriage that is prohibited because of idolatry. Therefore, the prohibition against marrying a Nochri applies to a Mamzer since there is a fear that the Nochri will lead his child astray. When that concern does not exist -- such as when the Nochri has converted -- the prohibition that applies after conversion is a prohibition of Yuchsin, lineage, which does not apply to a Mamzer.