Gezeirah

A takkanah (plural takkanot) is a major legislative enactment within halakha (Jewish law), the normative system of Judaism's laws.

A takkanah is an enactment which (1) revises an ordinance that no longer satisfies the requirements of the times or circumstances, or which (2), being deduced from a Biblical passage, may be regarded as new. It is, therefore, the antithesis of the Gezerah. Takkanot were framed even in the time of the Second Temple in Jerusalem, those of unknown origin being ascribed to earlier leaders, and they have been promulgated at all subsequent periods of Jewish history. The term is applied also to the institution provided for in the enactment.

Classical Jewish law granted rabbinic sages wide legislative powers. There are two powerful legal tools within the halakhic system:

However, the general term takkanah is used to refer to either gezeirot or takkanot.

Takkanot, in general, do not affect or restrict observance of Torah mitzvot. However, the Talmud states that in exceptional cases, the Jewish sages had the authority make a gezeirah even if it would "uproot a matter from the Torah". In Talmudic and classical halakhic literature, this authority refers to the authority to prohibit some things that would otherwise be biblically sanctioned (shev v'al ta'aseh). Rabbis may rule that a Torah mitzvah should not be performed, e.g. blowing the shofar on Shabbat, or blessing the lulav and etrog on Shabbat. These gezeirot are executed out of fear that some might otherwise carry the mentioned items between home and the synagogue, thus inadvertently violating a Sabbath melakha, a greater sin than neglecting the banned mitzvah.

Another rare and limited form of takkanah involved overriding Torah prohibitions. In some cases, the sages allowed the temporary violation a prohibition in order to maintain the Jewish system as a whole. This was part of the basis for Esther's relationship with Ahasuerus. (Sanhedrin)

Among the earlier takkanot are the institutions ascribed to Moses:

Other Biblical takkanot were ascribed as follows:

To the Prophets before the destruction of the Temple:

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