During his more than fifty-year writing career, American Jewish philosopher Horace Kallen (1882–1974) incorporated a deep focus on science into his pragmatic philosophy of life. He exemplified the hope among Jews that science would pave the way to full and equal integration. In this intellectual biography, Kaufman explores Kallen's life and illuminates how American scientific culture inspired not only Kallen's thought but also that of an entire generation. Kaufman reveals the ways in which Kallen shaped the direction of discussions on race, ethnicity, modernism, and secularism that influenced the American Jewish community. An ardent secularist, Kallen was also a serious religious thinker whose Jewish identity, as unique and idiosyncratic as it was, exemplifies the modern responsiveness to the moral ideal of "authenticity." Kaufman shows how one man's quest for authenticity contributed to a gradual shift in Jewish self-perception in America and how, in turn, his struggle led to America's embrace of Kallen's well-known term "cultural pluralism."