The Varieties of Religious Experience

William James's 1902 Gifford Lectures — examining religious experience empirically through case studies of mystical experiences, conversions, prayer, and saintliness — arguing that religious experience is a genuine category of human experience deserving scientific study regardless of theological truth claims.

Creates the psychology of religion as an empirical discipline — James's argument (that religious experience should be studied by its fruits rather than its roots, and that mystical states are genuine noetic states regardless of their theological interpretation) is the foundational document of the empirical study of religion.