It is important to note that not all names may be designated. There is, for example, a tradition that Ashkenazic Jews do not name their children after a living person. Yet, neither the Bible nor the Talmud make any reference to this prohibition. Indeed, just the opposite. The Lubavitcher Rebbe (Sha’arei Halacha U’Minhag, Yoreh De’ah, Volume III, p.298) notes that from verses in Genesis (See Genesis 11:24-26) it is evident that Terach (father of Abraham) named his son Nachor during the lifetime of his father, Nachor.
In addition, the Talmud (Shabbat 134a) records a case of a mother concerned about the circumcision of her third son after her two older sons died as a result of circumcision. Rav Natan gave sage advice that was followed and the child lived and was named “Natan HaBavli.” 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.
Yet, the Ashkenazic custom to refrain from naming children after living persons prevails. The following are several rationales for such a custom (some with sources, some without). Naming a child after a living person gives the impression that one wishes the namesake were dead, chas v’shalom (B’rit Avot 8:20, cited in the name of Noheig Katzon Yosef). When a child and his/her father [mother] or grandfather [grandmother] have the same name, the Angel of Death may, by mistake, kill the younger one rather than the forebear. According to Jewish law it is not deemed proper respect to call one’s parent by his/her first name (Yoreh De’ah 240:2). Giving a child the name of the living parent or grandparent would generate confusion and a belittlement of respect (Chelkat Yaakov, Yoreh De’ah 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.
Many years ago a family requested that I perform a wedding during the Nine Days leading up to Tisha B’Av. 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 curse of bad luck.
If so what is the reasoning of the Sefardim, who practice no such ban? Simply they never adopted any such customs. They follow the original tradition wherein it was completely permitted to name children after living persons. Indeed, they deem the act as a form of granting honor to parents, or grandparents.
There is, however, a rabbinic (Yoma 38b) rule prohibiting the naming of children with names of sinners or evildoers (resha’im). This prohibition has yielded two basic interpretations A simple understanding is that this is a practical means of expunging the names of Jewish sinners from usage. The implication is that there is a general ban against mentioning the names of the wicked and the practical vehicle to curtail such usage was to simply not name children after them.
Rabbenu Chananel (ad. loc.) notes that the prohibition against using the names of the wicked means that “any person so named will not be successful.” This implies a form of a curse. Any child named with the name of an evildoer will simply not be successful in life. What parent would wish to jeopardize the success of a child by disregarding the rabbinical ban? It may be assumed, without question, that parents will refuse to give children the names of sinners once they are aware of the projected doom for anyone so named. The uniqueness of Rabbenu Chananel’s position is that he introduced elements of mysticism and fear into the ordinary function of naming a child. As such, the proper name for children requires serious thought and should not be based upon whim.