Although developed from the Biblical ban, excommunication, as employed by the Rabbis during Talmudic times and during the Middle Ages, it became a rabbinic institution, the object of which was to preserve Jewish solidarity. A system of laws was gradually developed by Rabbis, by means of which this power was limited, so that it became one of the modes of legal punishment by rabbinic courts. While it did not entirely lose its arbitrary character, since individuals were allowed to pronounce the ban of excommunication on particular occasions, it became chiefly a legal measure resorted to by a judicial court for certain prescribed offenses.
The Talmudic form of cherem must be distinguished from that described in the Tanakh in the time of Joshua and the early Hebrew monarchy, which was the practice of consecration by total annihilation at the command of God carried out against peoples such as the Midianites, the Amalekites, and the entire population of Jericho. The neglect of Saul to carry out such a command as delivered by Samuel resulted in the selection of David as his replacement.
The Talmud speaks of twenty-four offenses that, in theory, were punishable by a form of niddui or temporary excommunication. Maimonides (as well as later authorities) enumerates the twenty-four as follows:
For all practical purposes, most of these conditions no longer were considered as grounds for a ban since the end of the Talmudic era, around 600 CE.
The "niddui" ban was usually imposed for a period of seven days (in Israel thirty days). If inflicted on account of money matters, the offender was first publicly warned ("hatra'ah") three times, on Monday, Thursday, and Monday successively, at the regular service in the synagogue. During the period of niddui, no one except the members of his immediate household was permitted to associate with the offender, or to sit within four cubits of him, or to eat in his company. He was expected to go into mourning and to refrain from bathing, cutting his hair, and wearing shoes, and he had to observe all the laws that pertained to a mourner. He could not be counted in the number necessary for the performance of a public religious function. If he died, a stone was placed on his hearse, and the relatives were not obliged to observe the ceremonies customary at the death of a kinsman, such as the tearing of garments, etc.
It was in the power of the court to lessen or increase the severity of the niddui. The court might even reduce or increase the number of days, forbid all intercourse with the offender, and exclude his children from the schools and his wife from the synagogue, until he became humbled and willing to repent and obey the court's mandates. According to one opinion, the apprehension that the offender might leave the Jewish fold on account of the severity of the excommunication did not prevent the court from adding rigor to its punishments so as to maintain its dignity and authority (Shulkhan Arukh, Yoreh Deah, 334, 1, Rama's gloss, citing Sefer Agudah). This opinion is vehemently contested by the Taz (ibid.), who cites earlier authorities of the same opinion (Maharshal; Maharam; Mahari Mintz) and presents proof of his position from the Talmud. Additionally, the Taz notes that his edition of the Sefer Agudah does not contain the cited position.
If the offense was in reference to monetary matters, or if the punishment was inflicted by an individual, the laws were more lenient, the chief punishment being that men might not associate with the offender. At the expiration of the period the ban was raised by the court. If, however, the excommunicate showed no sign of penitence or remorse, the niddui might be renewed once and again, and finally the "cherem," the most rigorous form of excommunication, might be pronounced. This extended for an indefinite period, and no one was permitted to teach the offender or work for him, or benefit him in any way, except when he was in need of the bare necessities of life.
A milder form than either niddui or cherem was the "nezifah" ban. This ban generally only lasted one day. During this time the offender dared not appear before him whom he had displeased. He had to retire to his house, speak little, refrain from business and pleasure, and manifest his regret and remorse. He was not required, however, to separate himself from society, nor was he obliged to apologize to the man whom he had insulted; for his conduct on the day of nezifah was sufficient apology. But when a scholar or prominent man actually pronounced the formal niddui on one who had slighted him, all the laws of niddui applied. This procedure was, however, much discouraged by the sages, so that it was a matter of proper pride for a rabbi to be able to say that he had never pronounced the ban of excommunication. Maimonides concludes with these words the chapter on the laws of excommunication:(Mishneh Torah, Talmud Torah, vii. 13).
Except in rare cases in the Haredi and Chassidic communities, cherem stopped existing after The Enlightenment, when local Jewish communities lost their political autonomy, and Jews were integrated into the greater gentile nations in which they lived.