Although developed from the Biblical ban, excommunication, as employed by the Rabbis during Talmudic times and during the Middle Ages, is really a rabbinic institution. Its object was to preserve Jewish solidarity. The legal instinct of the Rabbis made it impossible for such an arbitrary institution to become dangerous, and a whole system of laws was gradually developed, by means of which this power was limited, so that it practically became one of the modes of legal punishment by the court. 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.
Except in rare cases in the Ultra-Orthodox community, cherem stopped existing after The Enlightenment, when local Jewish communities lost their political autonomy, and Jews were integrated into the greater gentile nations which they lived in.
The only type of cherem which still exists is the social ban against praying with Jews for Jesus, or any of the other so-called Messianic Judaism members. Jews of all the modern Jewish denominations reject prayer with members of these groups, because most of these groups are Fundamentalist Protestant Chrisitian organizations attempting to convert Jews to Christianity. They are viewed as missionaries who are trying to end Judaism, one person at a time, by bringing people into Christianity. Members of these groups are thus turned away from membership in Jewish synagogues.
The Talmud speaks of twenty-four offenses that, in theory, were punishable by excommunication. This a round number which is not to be taken literally. Later authorities enumerate the twenty-four as follows:
(1) insulting a learned man, even after his death; (2) insulting a messenger of the court; (3) calling an Israelite "slave"; (4) refusing to appear before the court at the appointed time; (5) dealing lightly with any of the rabbinic or Mosaic precepts; (6) refusing to abide by the decision of the court; (7) keeping in one's possession an animal or an object that may prove injurious to others, such as a savage dog or a broken ladder; (8) selling one's real estate to a non-Jew without assuming the responsibility for any injury that the non-Jew may cause his neighbors; (9) testifying against one's Jewish neighbor in a non-Jewish court, through which the Jew is involved in a loss of money to which he would not have been condemned by a Jewish court; (10) appropriation by a priest whose business is the selling of meat, of the priestly portions of all the animals for himself; (11) violating the second day of a holiday, even though its observance is only a custom; (12) performing work on the afternoon of the day preceding Passover; (13) taking the name of God in vain; (14) causing others to profane the name of God; (15) causing others to eat holy meat outside of Jerusalem; (16) making calculations for the calendar, and establishing festivals accordingly, outside of Palestine; (17) putting a stumbling-block in the way of the blind, that is to say, tempting one to sin; (18) preventing the community from performing some religious act; (19) selling forbidden ("terefah") meat as permitted meat ("kasher"); (20) omission by a "shohet" (ritual slaughterer) to show his knife to the rabbi for examination; (21) self-abuse; (22) engaging in business intercourse with one's divorced wife; (23) being made the subject of scandal (in the case of a rabbi); (24) excommunicating one unjustly.
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 Palestine thirty days). If it was 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. 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, Isserles' gloss).
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).
Summary
Since the Enlightenment
In the Talmud
The Niddui
The cherem
The Nezifah