Mordecai Menahem Kaplan (June 11, 1881 – November 8, 1983) was an American Modern Orthodox rabbi, writer, Jewish educator, professor, theologian, philosopher, activist, and religious leader who founded the Reconstructionist movement of Judaism along with his son-in-law Ira Eisenstein.

[4] His father, ordained by the leading Lithuanian Jewish luminaries, went to serve as a dayan in the court of Chief Rabbi Jacob Joseph in New York City in 1888.

[2][3][5] Although affiliated with the most traditional Orthodox institutions and personalities in the Lower East Side, his father persisted in non-conformist openness to trends he had already exhibited in Russia: He hosted discussions in his home with maverick Bible critic Arnold Ehrlich,[1] withdrew his son from the Etz Chaim Yeshiva, enrolled him in public school, and later sent him to JTS to pursue studies to become a modern Orthodox rabbi.

[6] Kaplan's early education was strictly Orthodox, but, by the time he reached secondary school, he had been attracted to heterodox opinions (particularly regarding the critical approach to the Bible).

[1] In 1893, Kaplan began studying for ordination at the Jewish Theological Seminary (JTS),[5] which, at that time, was a Modern Orthodox institution founded to strengthen Orthodoxy and combat the hegemony of the Reform movement.

As he was already serving as a rabbi at this point, this created a high degree of dissonance resulting in considerable internal turmoil and anguish over the hypocrisy of practicing and preaching that which he no longer believed.

[6] His private diaries and papers reveal that he was tortured within because his beliefs about the nature of religion and of Judaism conflicted with his duties as the leader of an Orthodox congregation.

[2][3][5] Kaplan was not primarily interested in academic scholarship; but rather in teaching future rabbis and educators to reinterpret Judaism and make Jewish identity meaningful under modern circumstances.

Kaplan's Reconstructionist philosophy influenced not only his own immediate students, but through them, his extensive writings, and public lectures over several decades, the American Jewish community at large.

Many of his ideas, such as Judaism as a civilization (and not merely a religion or nationality); bat mitzvah; egalitarian involvement of women in synagogal and communal life; the synagogue as a Jewish center and not merely a place of worship; and living as Jews in a multicultural society, eventually came to be accepted as commonplace and implemented in all but strictly Orthodox segments of the community.

He was the leading educator to confront rabbis, teachers, and laity with the changes in Jewish thought that had become necessary once the Bible had been exposed to modern techniques of examination and interpretation.

[2][5][1][4] Kaplan's ideology and rhetoric had been evolving, over the decade, but it was not until 1920 that he finally took a clear and irrevocable stand, criticizing "the fundamental doctrine of Orthodoxy, which is that tradition is infallible...

[2][5][1][4] He held the first public celebration of a bat mitzvah in the United States, for his daughter Judith Kaplan, on March 18, 1922, at the Society for the Advancement of Judaism, his synagogue in New York City.

In 1935 a biweekly periodical (The Reconstructionist) was started under Kaplan's editorship, which adopted the following credo: “Dedicated to the advancement of Judaism as a religious civilization, to the upbuilding of Eretz Yisrael [the Land of Israel] as the spiritual center of the Jewish People, and to the furtherance of universal freedom, justice, and peace.” Kaplan further refined the goals of his ideology in subsequent books including: The Meaning of God in Modern Jewish Religion (1937), Judaism Without Supernaturalism (1958), and The Religion of Ethical Nationhood (1970).

[2][1] As a result, he was excommunicated by the Union of Orthodox Rabbis of the United States and Canada,[2][5] who held a herem ceremony at which his prayer book was burned.

As the years passed, the number of affiliates grew, but it was not until the late 1960s, that the movement actually became a separate denomination, when the Reconstructionist Rabbinical College opened its doors in 1968.

He then became involved in the Society for the Advancement of Judaism, where on March 18, 1922, he held (possibly) the first public celebration of a bat mitzvah in America, for his daughter Judith.

Four years later, seminary professors Alexander Marx, Louis Ginzberg and Saul Lieberman went public with their rebuke by writing a letter to the Hebrew newspaper Hadoar, lambasting Kaplan's prayer book and his entire career as a rabbi.

To believe in God means to take for granted that it is man's destiny to rise above the brute and to eliminate all forms of violence and exploitation from human society.