Mordecai Kaplan, the founder of the Reconstructionist movement, was the most influential and controversial radical Jewish thinker in the twentieth century. This book examines the intellectual influences that moved Kaplan from Orthodoxy and analyzes the combination of personal, strategic, and career reasons that kept Kaplan close to Orthodox Jews, posing a question crucial to the understanding of any religion: Can an established religious group learn from a heretic who has rejected its most fundamental beliefs?