Halakhah (Hebrew, from halek, «he went») is either a particular law, or the entire Jewish legal system. The halakhah, in its entirety, is believed to go back to Moses.
According to Mamonides, «In the two Talmuds and the Tosefta, the Sifra and the Sifrei, in all these are explained the permitted and the forbidden…as handed down from person to person from the mouth of Moses our teacher at Sinai.»
The halakhah is composed of the written law (the six hundred and thirteen commandments of the Pentateuch), the statements handed down by tradition (such as the words of the prophets and the hagiograph [Writings]), the oral law (which includes interpretations of the written law), the sayings of the scribes, and established religious custom. Written law is the Torah she-bi-khetav, the oral law is Torah she be’al peh (…by mouth).
In the days of the second Temple a major point of friction between the Pharisees and the Sadducees was the validity of the oral law since the Sadducees were only adhering to the written law. Even among the Pharisees, schools of teaching such as Hillel and Shammai differed in their interpretation of biblical law and in their own oral rulings.
Various attempts were made at drawing up collections of rulings. At the end of the second century AD, however, Rabbi Judah ha-Nasi summarized the legal debates in a form that came to be regarded as authoritative, and this record of the final decisions of the tannaim now constitutes the Mishnah. Once this work was established, further debate centered on its meaning and interpretation; these discussions of the Palestinian and Babylonian amoraim are recorded in the two Talmuds. In the Middle Ages, and subsequently, the halakhah was codified.
The final decisions of the Talmud and further responsa were collected in such volumes as the Maimonides’ Mishneh Torah (Second Law) and Joseph Caro’s Shulhan Arukh (The Land Table). The Shulhan Arukh in particular became so authoritative that there was a marked reluctance to part from its rulings.
Many see the dutiful acceptance of the authority of the halakhah as the distinctive essence of Judaism. According to the Orthodox, the halakhah is God-given and must be obeyed. The Progressive movements, while giving reverence to the halakhah, do not accept its binding obligation in every aspect of life. In so doing, the Progressive Jews are perceived by their Orthodox co-religionists as rejecting the point and purpose of tradition.
Hence Reform rabbis are not accepted as rabbis, and Reform proselytes are not considered to be Jews. Thus it is in their unconditional adherence to the halakhah, the Orthodox Jews define themselves and their commitment. A.G.H.
Bowker, John, The Oxford Dictionary of World Religions, New York, Oxford University Press, 1997, p. 404