William James made significant contributions to the disciplines of psychology and philosophy. His book The Principles of Psychology (1890) ushered in the modern era of American psychology by demonstrating that a truly scientific discipline has no need for such metaphysical or religious notions as a transcendental ego or a substantial soul. Although most of the specific doctrines of The Principles of Psychology have been superseded, James's pioneering work in such areas as the relationship of the brain to the mind, consciousness, emotion, habit, will, and belief continues to have influence. As a philosopher, James advocated the discipline's independence from dogmatic theology and worked to improve its teaching in American universities and colleges.

James's impact on his own generation went beyond the strength of his intellect. He was one of the most engaging characters of the day, numbering among his friends, acquaintances, and correspondents such luminaries as the jurist Oliver...