W. B. Yeats spent a great deal of his life immersing himself in magical, mystical, and philosophic studies in order, as he claimed, to devise a personal system of thought "that would leave [his] ... imagination free to create as it chose and yet make all that it created, or could create, part of the one history, and that the soul's." He succeeded in developing a cohesive metaphysics, and one which is surprisingly original. While he set it down in...