The Genesis of William James’s Psychology of Religion: From ‘The Principles of Psychology’ to ‘The Varieties of Religious Experience’

William James’s two psychological classics—The Principles of Psychology (1890) and The Varieties of Religious Experience: A Study in Human Nature (1902)—are widely read but rarely connected. How are James’s psychological theories in The Principles applied in The Varieties? Most scholars say they are not. Our thesis is that, throughout The Varieties, James uses The Principles as the foundation for his psychology of religion. His chapters in The Principles on the brain, habit, the stream of consciousness, the subconscious, the self, attention, association, and emotions all contain passages that anticipate the main themes of The Varieties. These include the psychological roots of a sense of unseen reality, conversion experiences, mystical experiences, saintliness as a character type, and other religious topics. This article highlights ten conceptual connections between the two classic texts. We show that James’s original and core psychological principles guided his approach to studying personal religious experience in The Varieties. In addition, some of James’s psychological principles were broadened and enriched through their interaction with religious data. By placing the two texts in conversation, a more precise and deeper understanding of James’s psychology of religion emerges.