When the mother is Jewish, but the father is not, how should the baby be named? Rema to Shulchan Aruch states that the baby should be named after the maternal grandfather. Question: Is there any source for the custom to name the baby ___ ben/bat Mother’s Jewish name?
There is a source for this, and if a parent’s name is to be used, the most appropriate would be the mother’s name.
There are four possible answers to this question: 1) calling the child after his mother’s name; 2) calling him after his maternal grandfather’s name; 3) calling him after Avraham; 4) calling him by a single name, and not after anybody.
Rema (Orach Chaim 139:3), concerning calling somebody up in shul, writes that an asufi (somebody whose father is unknown) is called up after his maternal grandfather.
Taz disputes this ruling, arguing that he should be called up after Avraham, and not after his maternal grandfather, which is liable to cause confusion should he even need to write a divorce document. Eliyah Rabba (4) defers the ruling of Taz, but the ruling is upheld by Chochmas Shlomo.
The rulings above, however, concern the question of calling a person up in shul, where a father’s name must be given, to save the person being called up from shame. With regard to writing a get (divorce document), Harei Besamim (tinyana 172) writes that somebody with a non-Jewish father should be named after his mother, citing a number of Talmudic precedents for the princple.
However, in both the case of calling somebody up to the Torah, and the case of the get document, there is a need to call the child after a parent–in the case of the get he needs to be clearly identified.
Yet, for the actual naming of a child, there would not appear to be a need to call the son after a parent at all, and the most simple option would seem to be to name him without referring to a parent. Indeed, Rema writes that for calling up to the Torah the person should not be called up without the name of the parent, for fear of causing him shame, implying that were there no concern, the individual would be called by his own name alone.
However, if there is reason to name the child after a parent — for instance, at a ceremony where it might be embarrasing not to — the most authentic name to use would be the mother’s name, as one would for writing a get. If one wishes to use a male name, then one may follow the ruling of Rema, and call the child by his maternal grandfather’s name.