It is a widespread Ashkenazi minhog not to name a child after someone who is living. From where can this custom be sourced? Why is this so?
I would assume it is because it has some negative kabbalistic significance.
Various reasons why Ashkenazim do not name after a living person are given by Rabbi Simcha Cohen gives a set of answers. He points out that Nachor son of Terach was named after his (living) grandfather. He also points out at least one rav who was honored by having a baby named in his honor. One of the sources for this minhag can be seen in Sefer Chassidim 460; Shaarei Halachah Uminhag, vol. 3, p. 298.
My mother-in-law shared a name with my father-in-law's mother. When it came time to name my eldest daughter, they were very careful to make sure that we did not use a middle name and that we used the Yiddish spelling and pronunciation rather than the Hebrew spelling and pronunciation. The superstition expressed was that if the two were given the same name, the Malach Hamaves would show up to take one of them within the year (probably the older one).
Click here for an Orthodox answer by Rabbi Simcha Cohen
The Bible and the Talmud do not contain any reference to this prohibition. Indeed, just the opposite, the Lubavitcher Rebbe notes that from verses in Genesis it is evident that Terach (father of Abraham) named his son Nachor during the lifetime of his father Nachor.(See Genesis 11:24-26; Sha'arai Halacha U’Minhag,Yoreh Deah, Volume III, p.298)
In addition, the Talmud records a case of a mother concerned about the circumcision of her third son whose two older son’s died as a result of circumcision. Rav Natan gave sage advice that was followed and the child lived and was named “Natan HaBavli”. (Shabbat 134a) The overt indication appears to be that the name given to the child after the Rav was an act of honor to the Rav and certainly not a sinful act.
However, he then explains that Ashkenazim began following this custom for various reasons.
In Ashkenazic Europe the custom developed to refrain from naming children with the names of living persons. The following rationales are presented.(Some with sources, some without.).
Common custom is to name children after parents or grandparents who are no longer alive. To name a child after a living person gives the impression that one wishes they were dead, Chas V’Shalom.- (B’rit Avot 8:20 cited in the name of Noheig Katzon Yosef) When a child, together with his/her father or grandfather have the same name, the Angel of Death may, by mistake, kill the youngest rather than the father or grandparent.
According to Jewish law it is not deemed proper respect to call one’s parent by his/her first name.(Yoreh Deah 240:2) Giving a child the name of the living parent or grandparent would generate confusion and a belittlement of respect.(Chelkat Yaakov, Yoreh Deah 136,Shmirat HaGuf V’haNefesh, Vol. II, 154:9) To forestall such errors, Ashkenazim simply did not name children after a living person.
Thus, concern for proper respect for parents, mysticism, coupled with fear of the “evil eye”, serve as the basis for the custom. There never was an official rabbinic law to outlaw naming a child after a living person. It is merely a custom that has prevailed comparable to a rabbinical ban. (It is merely an extension of the mystic position of Rabainu Chan’anel.)
Many years ago a family requested that I perform a wedding during the Nine Days commemorating the destruction of the holy Bet HaMikdash. I mentioned that according to jewish law one was not to be married during this period of time. To this they responded that they were not too religious and were not perturbed about violating the law. When I mentioned that it was deemed “Bad Luck” to get married at that time, they immediately changed the date for the wedding. In other words even Jews who are not observant on a regular basis will not be involved with any matter shadowed by the spectre of “Bad Luck”. So too with the Ashkenazic ban against naming a child after living persons. No one wishes to galvanize “Bad Luck” upon their children.(Kashe sakanta m’isurah)
The Sefardim simply never adopted any such customs. They follow the original tradition wherein it was totally permitted to name children after living persons. Indeed, they deem the act as a form of granting honor to parents or grandparents.
I agree with the statement that the Bible and Talmud state no rule on point. But does the Talmud offer no evidence of the prevailing custom? After all, we all remark on the customs of Sephardim and Ashkenazim partly because of direct experience. If we know of Sephardim with living namesakes, but not Amoraim with living namesakes, that would seem prima facie evidence that the custom is more common amongst Sephardim than amongst Amoraim.
I know of some references in the Gemara to people named for their grandfathers (stated here with ArtScroll page numbers): Abba the son of Chiya Bar Abba (Berachos 43b4, Shabbos 121b3, Avodah Zarah 13b3 #30); Dortai the son of Yehudah Ben Dortai (Pesachim 70b2); Horkenus the son of Eliezer Ben Horkenus (Shabbos 127b1); Zevadyah the son of Ya'akov Bar Zavdi (almost the same name) (Yerushalmi Berachos 10b1). And let's not forget the clear examples of Shimons and Gamliels, and the puzzling example of Abaye. But I don't know of examples of parents giving their own names or those of anyone in their own generation or their children's generation. Why is that?
The pattern of (at least occasionally) naming for grandfathers but apparently no other relatives seems more consistent with the theory that in the world of Chazal naming for the living was rare.
I realize that this does not offer a theory of WHY they avoided such names. I'm not sure that was your question, and I don't have an answer to that. And I also realize that the "negative" evidence (of failing to see something) is not an extremely strong case. But it's something.