This article is about J. R. R. Tolkien's adaptation of Pythagorean musical elements in the ‘Song of the Ainur’ of the Silmarillion. It details Tolkien's use of Pythagorean dissonance, along with what that amounts to in terms of musical theory, and explores the epistemological origins of the concept and how it found its way into this work of fiction. On the latter point, Platonism, Neoplatonism, and early Christian theology are considered. This includes the likes of Prudentius, pseudo-Dionysius, Augustine, and Aquinas, among others. The article observes that Tolkien has deliberately chosen a somewhat esoteric element of Pythagorean musical theory, albeit highly relevant to his own historical context, in order to explore concepts of morality along with the traditional, Christian conundrum of predestination vs. free will.