Halakhah: Sources and Development
From biblical law, through classic rabbinic debate and medieval law codes, and continuing in the modern period, Jewish law has undergone constant development.
Reprinted with permission from Louis Jacobs, The Jewish Religion: A Companion, published by Oxford University Press.
The main source of the halakhah [Jewish law] is, of course, the Pentateuch [the Torah], which contains three codes of law (Exodus 21-23, Leviticus 19, Deuteronomy 21-25), and particular laws in other parts of the work. The prophets also refer here and there to laws not found in the Pentateuch but, in the rabbinic scheme, no prophet was ever authorized to introduce new laws and, on this view, the prophets are simply recording the "law of Moses;" that is, although these laws are not actually found in the Pentateuch, they, too, were [considered] given, together with the laws found there, by God to Moses, either on Mount Sinai or subsequently during the 40-year journey through the wilderness.
Written and Oral Torahs, Biblical and Rabbinic Laws
This is the rabbinic doctrine of the two Torahs, the Written Torah of the Bible, supplemented and interpreted by the Oral Torah. The Oral Torah denotes both those interpretations of the Pentateuchal laws handed down by tradition from Moses and the exegesis [explication and interpretation] of the laws by the Jewish sages. In addition, the sages of Israel are seen as possessing the authority to introduce new legislation.
Laws which stem from the Written and Oral Torah are referred to as biblical laws [in Aramaic, mi-de'oraita]; laws introduced by the sages are termed rabbinic laws [in Aramaic, mi-derabbanan]. There are technical differences between the two types of law--for instance, cases of doubt with regard to biblical law are treated strictly, those with regard to rabbinic law, leniently.
The Talmudic Record and the Legal "Bottom Line"
All this material, the oral law and the rabbinic legislation, are found in the Talmuds, Babylonian [in Hebrew, Bavli] and Palestinian [called in Hebrew the "Jerusalem Talmud" or Yerushalmi], and in the other rabbinic sources known as the halakhic midrashim [interpretations]. Although, in the early period, the Sadducees [one of the sects of Second Temple Judaism] rejected the whole doctrine of the Oral Torah, and much later [in early medieval times], the Karaites rejected the Talmud, it is the [Babylonian] Talmud that became the ultimate source of the halakhah as traditionally conceived.
The problem is that in the Talmud and the rabbinic literature in general, there are numerous debates among the rabbis on the questions of interpretation so that, as the Talmud [itself] states, it is difficult to find a clear halakhah [in the sense of specific law] anywhere. The Talmud is not a code of law but a gigantic work containing all the debates and elaborations, largely in a purely academic form.