Sources: Mishnah Avot 1:1; Talmud Bavli Shabbat 31a (Hillel’s summary); Gittin 60b (the prohibition on writing oral law); Exodus 34:27; Deuteronomy 17:8–13 (the authority of the judges).

The doctrine of Oral Torah (Torah she-be-al peh) holds that at Sinai, God gave Moses both the written Torah and an oral explanatory tradition — transmitted generation by generation through an unbroken chain: Moses to Joshua to the Elders to the Prophets to the Great Assembly to the Pharisees to the Tannaim to the Amoraim. Avot 1:1 opens the rabbinic corpus with this genealogy of authority. This doctrine accomplishes several crucial things simultaneously: (1) It grounds rabbinic authority — the rabbis interpret the Torah not as innovators but as custodians of a tradition going back to Sinai; their rulings are not legislation but unfolding of what was always implicit in the revelation; (2) It enables legal development — the oral tradition can adapt to new circumstances precisely because it was never frozen in a single written document; (3) It explains apparent contradictions and gaps in the written Torah — wherever the text is silent or unclear, the oral tradition fills the gap; (4) It creates the rabbi’s authority over the priest’s — the post-Temple world needs legal interpreters, not cult administrators. Shabbat 31a records the famous exchange: a non-Jew asks Hillel to teach him the whole Torah while standing on one foot. Hillel says: ‘What is hateful to you, do not do to your neighbor. That is the whole Torah; the rest is commentary — go and learn.’ The oral tradition enables this summarization and application. Karaism’s 8th-century rejection of the oral Torah is the most consequential internal Jewish theological dispute after 70 AD.