In the first section of this paper I present Santayana's system of philosophy as an inquiry into what Peter Strawson called "descriptive metaphysics" (as opposed to "revisionist metaphysics"), and show its connection with naturalism. The second section outlines Santayana's version of naturalism considering his criticisms of Spinoza and Dewey as deviated or "unbalanced" naturalist philosophers. Central to this point is Santayana's original way of inserting the "realm of matter" and "the realm of spirit" in a consistent metaphysical picture, although, in the third section, I argue that the naturalist view thus achieved does not allow an account of meaning and of truth in terms of the other two realms of being postulated by Santayana: the realm of essence and the realm of truth.