Gemara

"V'Lo Sischaten Bam" teaches that there is no Kidushin with the seven nations. "He will veer your son (away from Me)" includes all (Nochrim,) who make veer.

Question: This is like R. Shimon, who derives laws based on the reason for Mitzvos. What is Chachamim's source for other nations?

Yevamos 76a (Beraisa): A Petzu'a Daka Yisrael may marry a Nesinah (a convert from the seven Kena'ani nations).

(Rav Sheshes): He lost his Kedushah, so "v'Lo Sischaten Bam" does not apply.

Objection (Rava): The Isur does not depend on Kedushah, rather, lest the children serve idolatry! The Isur applies to Nochrim. After conversion the Torah permits them. Chachamim forbade only people who can have children.

Retraction (Rava): "V'Lo Sischaten Bam" applies only after conversion. Before this, marriage does not take effect!

Question (Rav Yosef): "Va'Yischaten Shlomo Es Bas Paro, Melech Mitzrayim".

You cannot say that she converted, for a Mitzris Rishonah is forbidden!

Answer (Rav Papa): Shlomo did not marry Bas Paro - "the forbidden nations ... Shlomo clung to love (not marriage)".

78b (Mishnah): Nesinim are forbidden forever, both males and females.

(Rav Chana bar Ada): David decreed against the Nesinim - "the king ... said that the Giv'onim are not from Benei Yisrael."

79a - Questions: Moshe decreed against them - "from the woodchopper to the one who draws your water"! Yehoshua decreed against them - "Yehoshua made them woodchoppers and water drawers for the congregation and the Mizbe'ach"!

Answer: Moshe decreed for his generation. Yehoshua decreed only for when there is a Mikdash. David decreed forever, even when there is no Mikdash.

Avodah Zarah 36b (Rav): Nochriyos were forbidden in the 18 decrees.

Question: They are forbidden mid'Oraisa - "v'Lo Sischaten Bam"!

Answer #1: Mid'Oraisa, only the seven Kena'ani nations are forbidden. They decreed against all other Nochrim.

Question: R. Shimon forbids all Nochrim mid'Oraisa. How can he answer?

Answer #2: Mid'Oraisa, one may not live with a Nochris Derech Ishus (like one lives with a wife). They decreed against Zenus (extramarital relations).

Rishonim

Rambam (Hilchos Isurei Bi'ah 12:1): If a Yisrael had Bi'ah with a Nochris from other nations, Derech Ishus, they are lashed mid'Oraisa - "do not intermarry with them. Do not give your daughter to a Nochri's son, and do not take a Nochri's daughter for your son." This applies to the seven nations, and all of them. Ezra said "we will not give our daughters to the people of the land, and we will not take their daughters for our sons."

Magid Mishneh: Rava said that marriage applies only after conversion. The Meforshim explain that the Torah forbids anything in the way of marriage.

Rambam (Hilchos Isurei Bi'ah 12:22): The Torah does not forbid a convert from the seven nations from entering the Kahal (marrying a Yisrael). Of the seven, only the Giv'onim converted. Yehoshua decreed that their males or female not enter the Kahal as long as there is a Mikdash.

Magid Mishneh: The Rambam rules like the Sugya in Yevamos (78b), which forbids Nesinim mid'Rabanan. He holds that it argues with Rava (76a), who forbids mid'Oraisa.

Rambam (24): David decreed that they not enter the Kahal even when there is no Mikdash.

Poskim

Shulchan Aruch (EH 4:1): Nesinim and Nesinos are forbidden for all generations.

Beis Yosef (16 DH u'Mah she'Chosav Rabeinu v'Nir'eh): The Tur says that "do not intermarry with them" applies only to the seven nations, for the Halachah does not follow R. Shimon. Also, even for the seven nations, Rava concluded that the Torah forbids only after conversion. There is no marriage beforehand! The Rambam rules like R. Shimon because the Stam Gemara answered like him (and later answered for Chachamim). Since we expound the reason, lest he veer the children away from Hash-m, this applies only before conversion. Rava said oppositely according to Chachamim. Even if Rava said so according to everyone, the Halachah does not follow his calculation, rather, like he thought at first. The Gemaros in Kidushin and Avodah Zarah are like he thought at first.

Beis Yosef (DH v'Rashi): Rashi says that Nesinim, i.e. Giv'onim, are forbidden mid'Rabanan. If so, the Halachah does not follow Rava (who says that the Isur is after conversion). Rather, converts are permitted, except for the Nesinim. The Rambam (12:22) agrees. Others forbid the seven nations even after conversion, like Rava. This refers to the converts themselves. David decreed to forbid all generations. Rashi in Sanhedrin and Makos says that v'Lo Sischaten applies to Nochrim and Nesinim.

Beis Yosef (DH u'Mah she'Chosav Rabeinu v'Eino): Tosfos says that marriage applies only after conversion. The Gemara in Avodah Zarah and Kidushin cited "v'Lo Sischaten" to teach about the Isur to Nochrim. Really, it refers to the end of the verse "do not give your daughter to a Nochri's son, and do not take a Nochri's daughter for your son." The text does not say 'there is no Chitun (marriage) with them', for this implies that we expound "v'Lo Sischaten". R. Tam says that the text should say 'you have no Likuchin (Kidushin) with them', which implies that we expound the Seifa.

Prishah (4): One is liable for a convert of the seven nations for Bi'ah even not Derech Ishus. Do not say that "do not take" connotes Kidushin. The Rambam needed to learned from "Tischaten" that the Torah discusses Derech Ishus!

Gra (2): In CM 97:14, we rule unlike R. Shimon (who expounds the reasons for Mitzvos). Also, we rule like Rav Sheshes and Rava's conclusion in Yevamos, that the verse forbids after conversion. Tosfos explains that David decreed slavery on them. The Ramban says that the Torah forbids only the converts themselves, and David decreed for all generations.