This book would never have been written had I not been honored with an appointment as Gifford Lecturer on Natural Religion at the University of Edinburgh. In casting about me for subjects of the two courses of ten lectures each for which I thus became responsible, it seemed to me that the first course might well be a descriptive one on "Man's Religious Appetites," and the second a metaphysical one on "Their Satisfaction through Philosophy." But the unexpected growth of the psychological matter as I came to write it out has resulted in the second subject being postponed entirely, and the description of man's religious constitution now fills the twenty lectures. In Lecture XX I have suggested rather than stated my own philosophic conclusions, I hope to be able at some later day to express them in more explicit form.