sentences:  The work is considered to be the most complete expression of Santayana's moral philosophy; by contrast, his later "magnum opus", the four-volume "The Realms of Being", more fully develops his metaphysical and epistemological theory, particularly his doctrine of essences.Santayana's philosophy is strongly influenced by the materialism of Democritus and the refined ethics of Aristotle, with a special emphasis on the natural development of ideal ends.