Mordecai M. Kaplan, the founder of the Reconstructionist movement, was the most influential and controversial radical Jewish thinker in the 20th century. Examining the intellectual influences that prompted Kaplan to reject fundamental Orthodox precepts, Jeffrey S. Gurock and Jacob J. Schacter ask 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? More than a biography, A Modern Heretic and a Traditional Community is also a social history of American Orthodoxy and of American Judaism over the last century. It demonstrates the wide range of beliefs and practices Orthodoxy allowed in America and makes a distinct contribution to the fabric of American social history, Judaism and the history of religion in the United States.