KAPLAN, MORDECAI (1881–1983), American rabbi, author, and religious leader, was the creator of the theory of Reconstructionist Judaism and the founder of the Reconstructionist movement. The son of Rabbi Israel Kaplan, a Talmudic scholar, Mordecai Menahem Kaplan was born in Svenciony, Lithuania, on June 11, 1881. The family left eastern Europe in 1888 and reached the United States in June 1889. Kaplan was instructed in traditional Jewish subjects by private tutors while attending public schools in New York City. He received degrees from the City College of New York (1900) and Columbia University (1902) and rabbinic ordination from the Jewish Theological Seminary of America (1902). In 1909, following a tenure as minister and rabbi of Kehillath Jeshurun, an Orthodox congregation in New York City, Kaplan returned to the Jewish Theological Seminary, where he served for more than fifty years, first as principal (later dean) of the Teachers Institute until 1945, then as professor of homiletics and...