A famous debate arose in the academy between Rabbi Eliezer and Rabbi Yehoshua over the ritual status of a particular oven, called the oven of Akhnai. The technical question has become secondary in Jewish memory. What mattered was the argument about how halakhah is decided.
Rabbi Eliezer had every reason to believe he was right. He produced argument after argument. The other sages, led by Rabbi Yehoshua, rejected each one. Rabbi Eliezer turned to nature for help. "If the law is as I say, let this carob tree prove it," he declared. The carob tree tore itself out of the ground and traveled a hundred cubits down the field. "A tree cannot settle a legal question," the sages said.
"Let the stream of water prove it," Rabbi Eliezer said. The stream reversed course and began to flow backward. "A stream cannot settle a legal question," the sages said.
"Let the walls of the academy prove it," he said. The walls of the study hall bent inward, as if to fall. Rabbi Yehoshua rebuked even the walls, telling them not to intrude on a legal dispute among scholars. Out of respect for both rabbis, the walls stopped leaning, but neither fell back into place.
Finally Rabbi Eliezer cried, "Let heaven itself prove it!" A bat kol, a voice from heaven, answered and said, "Why do you argue with Rabbi Eliezer? The law is in accordance with him in every place!" Rabbi Yehoshua rose and quoted Deuteronomy 30:12, "It is not in heaven." The Torah has already been given. It is no longer in heaven's hands. The sages vote.
The majority ruled against Rabbi Eliezer, and in the aftermath they imposed a form of excommunication on him. Rabbi Akiba was chosen to carry the difficult news. A dearth fell on the land. Rabban Gamliel, Eliezer's brother-in-law and the presiding authority, was nearly drowned in a storm at sea. The sages had done what they did, they explained, not out of malice but to prevent factions. The Exempla preserves this scene drawn from Bava Metzia (59a–b).