In this classic work William James explores the psychology of religion, applying the scientific method to a field that had previously been treated as theoretical, abstract philosophy. James believed that individual religious experiences, rather than the precepts of organized religions, were the backbone of the world's religious life. His discussions of conversion, repentance, mysticism, and saintliness and his observations on actual, personal religious experiences all support this thesis. In his introduction, Martin E. Marty discusses how James's pluralistic view of religion led to his remarkable tolerance for extreme forms of religious behavior, a willingness to take risks in formulating his own theories, and a welcome lack of pretentiousness in his observations on how an individual stands in relation to the divine.