Kaplan contended in “Judaism as a Civilization: Toward a Reconstruction of American-Jewish Life” (1934) that for Judaism to remain vital it must evolve and speak to new generations or risk becoming static and stale. Adaptation was the answer, and in one book after another he suggested how to do just that. His best-known innovation—his introduction, in 1922, of the modern bat mitzvah, to mark the 12th birthdays of Jewish girls—is now standard practice in all but Orthodox synagogues. His bent toward reframing traditional Jewish prayers and holidays to reflect current social and ethical concerns remains refreshingly relevant.