for people who visit or move to a locale where the custom differs from their own.) Hasidim tend to follow their own minhagim. Within these broad categories there are also sub-groups by origin (e.g. Lithuanian or Polish or German customs), by location (e.g. "minhag Yerushalayim") or by branch (e.g. Skverrer Hasidim follow different customs than Chabad Hasidim). Families and even individuals may adhere to specific minhagim not followed by others. Discussion in rabbinic literature Various sources in rabbinic literature stress the importance of a long-held tradition, culminating in the statement "the minhag of our fathers is [equivalent to] Torah". Custom can thus determine halachic practice in cases of disagreement among rabbinic authorities. In numerous instances, Rabbi Moses Isserles warns that one should not abolish long-held customs. (Isserles' gloss on the Shulchan Aruch was, in fact, written so as to delineate Ashkenazi minhagim alongside Sephardi practices in the same code of law.) Despite the above, a minhag does not override clear biblical or talmudic enactments, and one may not transgress the latter for the sake of the former. In fact, any minhag that intrinsically involves an element of halakha violation is considered null and void. The Talmud rules that a valid minhag accepted by previous generations of a family or community is binding upon all later generations. The Rosh states that the Talmud's ruling fundamentally applies to practices undertaken by learned individuals; innovations by the unlearned need only be followed publicly. Other halakhic authorities hold that the Talmud's ruling applies to all valid practices initiated by either learned or unlearned individuals. In most cases, personal acceptance of a new minhag is tantamount to vowing performance of that minhag. Consequently, abandonment of such a minhag typically requires hatarat nedarim or sh'eilat chakham, halakhic procedures for absolving oneself from oaths. This was often necessary when, for example, an Ashkenazi Jew moved to the Ottoman Empire and wished to join the local Sephardi community. Changing minhagim Jewish law provides for a number of mechanisms to change or remove a custom when it is held to be mistaken or illogical. Orthodox rabbi and historian of Jewish law Menachem Elon writes: Custom, because of its spontaneous and undirected nature, sometimes calls for a measure of supervision and control. At times a custom may be founded on error, or develop unreasonably or illogically in a certain direction, or may even be in conflict with substantive and fundamental