Reprinted from The Jewish Religion: A Companion, published by Oxford University Press.
A mamzer is a child that is the issue of an adulterous or incestuous union. The law of the mamzer is stated in the verse: ‘A mamzer shall not enter into the congregation of the Lord; even to his tenth generation shall he not enter into the congregation of the Lord (Deuteronomy 23:3).’
Whatever the original meaning of the word mamzer, in the Rabbinic tradition, as finally recorded after much discussion, the mamzer is the offspring of an adulterous or incestuous relationship, for example, of a man and a married woman or of a brother and sister, and ‘entering the congregation of the Lord’ is understood to mean that the mamzer (or mamzeret, for a female) is forbidden to marry a Jew.
Since the verse states ‘even to his tenth generation,’ this is taken to mean that the taint is transmitted over all the mamzer’s generations so that the child of a mamzer, his grandchildren, and great-grandchildren may not marry into the Jewish community.
Apart from the disqualification with regard to marriage, the mamzer suffers no disabilities in Jewish law. He inherits, for instance, the estate of his natural father. The translation of mamzer as ‘bastard’ or ‘illegitimate child’ is consequently incorrect so far as Jewish law is concerned.
Ethical & Practical Issues
The fact that an innocent child is penalized in this way through no fault of its own has always presented a severe theological and ethical problem. On the practical level, any proliferation of mamzerim could result in the Jewish community being split into two groups, the members of one being disallowed from marrying the members of the other.
Because of these problems there is a distinct tendency throughout the history of Jewish marriage law to discover legal remedies to prevent the mamzer being exposed or declared as such.
Isserles in his gloss to the Shulhan Arukh (Even Ha-Ezer, 2.15) states, on the basis of Talmudic rulings: ‘If one who is unfit has become mixed in a particular family, then once it has become mixed it has become mixed and whoever knows of the disqualification is not permitted to disclose it and must leave well alone since all families in which there has been an admixture will become pure in the future.’
The last remark refers to a Talmudic statement that in the Messianic age the taint of mamzerut (the abstract term for the mamzer situation) will be removed.
In lands where there is civil marriage it is not uncommon for a married woman who has been divorced in civil law to remarry in civil law without obtaining a get, the Jewish bill of divorce, from her first husband. Any children born to her from the second marriage are technically mamzerim, rendering the problem in modern times far more acute than in the time when civil marriage and divorce were unknown.
Reform Judaism rejects the whole concept of mamzerut. Many Conservative and all Orthodox Rabbis do accept the traditional law in this matter but generally follow the Talmudic precedence of adopting various legal remedies in order to avoid the taint of mamzerut, and the ruling of Isserles is also followed that no investigation is to be made in order to expose mamzerut.
It is certainly contrary to the tradition to compile, as unfortunately some few Orthodox Rabbis do, a register of mamzerim.