We have already seen the position taken by Rabbi Akiva (see daf 64) who rules that any sexual relationship that is forbidden by the Torah – even a simple prohibition that will not carry with it the punishment of karet or mitat beit din – will preclude the possibility of marriage. Not only is marriage forbidden, but if it is attempted it will have no meaning or significance – like a brother who tries to marry his sister – and there will be no need to end the marriage with a divorce. Children born from such a relationship would be mamzerim. Rabbi Akiva’s position is not accepted as the halakha, and we distinguish between the more serious cases of incest and adultery, where the punishment is karet or mitat beit din and a simple prohibition (e.g. a kohen who marries a divorcee), where the couple is recognized by the halakha as being married, and the children will not be mamzerim.
The source offered by Rav Pappa for the rule that people who are not allowed to get married because of a lav (a simple prohibition) will still have their marriage recognized by the halakha is a passage that deals with inheritance laws. The pasuk says that if a man has two wives, one who is loved and one who is hated, and that each have sons, the man cannot offer a preferred inheritance to the son of the beloved wife, passing over the unloved wife’s son if he is the first-born ( 21:15) . Our Gemara notes that the wives are referred to as “loved” and “hated.” Since the Torah cannot possibly assume that God loves one wife more than the other, it must mean that one wife is from a permitted relationship and one is from a forbidden relationship. Nevertheless, the Torah views them both as being married to the man.
The obvious problem with this source is that the simple meaning of the Torah is that the wives are ahuvah (“loved”) and senu’ah (“hated”) by their husband, not by God. Rashi explains that we would not have thought that the husband could change the laws of inheritance based on his own preferences, so the only explanation is that this is a reference to a status based on some outside factor. The She’iltot suggests that it is the Torah’s use of ahuvah and senu’ah without reference to the husband that indicates that there is something objectively different about the wives having nothing to do with their husband’s likes or dislikes.