The Torah (Debarim 23:3) forbids marrying a Mamzer – somebody born from certain kinds of illicit relationships, such as adultery – or a Mamzeret – a female Mamzer. The descendants of a Mamzer are also forbidden for marriage. Although the Torah forbids marrying "even the tenth generation" of a Mamzer, which might imply that after the tenth generation the descendants are permissible for marriage, this is not the case. Rather, this means that the descendants are forbidden forever, even beyond the tenth generation.
If a man marries a Mamzeret, what is the status of the marriage? Clearly, this union is forbidden and they transgress a Torah prohibition. But does the marriage have a legal status of marriage?
Halacha establishes that if a person marries somebody whom the Torah forbids for marriage on the level of an "ordinary" prohibition, then the marriage is binding. There are certain forbidden relationships which the Torah designates as capital offenses, whereas others – such as marrying a Mamzer or Mamzeret – are forbidden on the level of a standard Torah prohibition. In the latter case, even though the marriage violates Torah law, the man and woman are Halachically considered married. Since the marriage is not a capital offense, the marriage takes effect, despite the prohibition violated. Hence, if a man marries a Mamzeret, and then decides to terminate the marriage, he must give the wife a Get and follow all the usual Halachic procedures for divorce. He cannot say that since the marriage was forbidden, it never legally took effect in the first place. In the case of a marriage to a Mamzeret, the marriage – though forbidden – is legally binding, and therefore it cannot be terminated without a Get.
The Sages inferred this Halacha from a verse in the Book of Debarim (21:15), where the Torah writes, "If a person has two wives, one who is beloved and one who is despised…" It seems difficult to understand why the Torah would concern itself with the husband’s preference of one wife over the other. This detail does not seem to be of any significance in the context of this verse. Furthermore, the Torah curiously describes the women as "beloved" and "despised," rather than saying, "he loves one and despises one." These peculiarities led the Sages to conclude that the Torah refers here to a case where the marriage to one woman is "beloved" by God, and the marriage to the other is "despised" by God – meaning, one marriage is permissible, and the other is forbidden. The Torah thus speaks of a man who married one woman whom he is allowed to marry, and another woman whom he is not allowed to married. Yet, the Torah considers them both the man’s wives – indicating that both marriages are binding, even the forbidden marriage. This demonstrates that in certain situations of a forbidden marriage, the man and woman are formally considered married despite the violation they commit.
If a man marries a Mamzeret and begets children from her, what is the status of the children?
Generally speaking, personal status is passed patrilineally – through the father. If one’s father is a Kohen, then he is a Kohen, even though his mother is not a daughter of a Kohen. And if the father is a Yisrael, then the son is a Yisrael, even if the mother is a daughter of a Kohen. This principle is derived from a phrase mentioned numerous times in the Book of Bamidbar, "Le’mishpehotam Le’bet Abotam" ("according to their families, the house of their fathers"), which indicates the family status is determined based upon the status of the father. Seemingly, then, in the case of a regular Jewish man who marries a Mamzeret, we should conclude that the children receive the father’s status, not the mother’s, and they are therefore normal Jews who are allowed to marry.
In truth, however, the children of such a marriage are, in fact, Mamzerim. A "Pesul" – a status of invalidity for marriage – is passed to a child by a father or a mother. The principle of patrilineal descent applies only to a proper, acceptable marriage, such as when a Kohen marries a non-Kohen, or a Kohen marries a Levi, and so on. But in the case of somebody whom Jews are forbidden to marry, either parent passes this status to the children. Therefore, if a man marries a Mamzeret, the children have the status of Mamzerim, and are forbidden to marry.
Summary: If a man marries a Mamzeret, in violation of Torah law, the marriage is nevertheless binding, and they therefore require a proper, Halachic divorce in order to dissolve the marriage. The children of such a marriage have the status of Mamzerim and may not marry.
