2,179. Out of Wedlock

Hilchos Issurei Biah 15:10

There are three types of mamzer: a definite mamzer, a doubtful mamzer and a mamzer under rabbinic law. A definite mamzer is the offspring of a union that was definitely incestuous or adulterous, as has already been discussed. A doubtful mamzer is the offspring of a relationship that may or may not have been adulterous or incestuous, such as if a man was intimate with a betrothed woman but we’re unsure if the betrothal was effective, or if a man was intimate with a divorced woman but we’re unsure if the divorce was effective, and similar such cases. An example of a mamzer under rabbinic law is if a woman heard that her husband died so she remarried but her husband later turned up alive. If her original husband was intimate with her while she was still married to the second husband, any offspring produced is a mamzer under rabbinic law.

Hilchos Issurei Biah 15:11

If an unmarried woman becomes pregnant through promiscuous relations, we ask her the status of the baby. If she replies that it’s the child of an acceptable person and that she was intimate with a Yisroel (an Israelite), her word is accepted and the child is halachically valid. This is so even if most of the residents of the city where she became pregnant were of halachically unfit descent.