One of the earliest acknowledgments of the significant metaphysical dimension to Tolkien’s thought also contains, notably enough, the first reference that I have found to Tolkien’s alleged Thomism. In 1972, the year prior to Tolkien’s death, professor and literary critic Paul H. Kocher raised the question as to “how far Tolkien wishes his treatment of evil to be considered not only moral but metaphysical.”
Without using blatantly theological terms his ideas are often clearly theological nonetheless, and are best understood when viewed in the context of the natural theology of Thomas Aquinas, whom it is reasonable to suppose that Tolkien, as a medievalist and a Catholic, knows well. The same is true in the area of metaphysics. Some of Thomas’s less specifically Christian propositions about the nature of evil seem highly congruent with those which Tolkien expresses or implies in laymen’s terms in The Lord of the Rings.
His perceptive point that Tolkien’s philosophy may be “best understood” in light of the thought of St. Thomas notwithstanding, Kocher curiously goes on to say very little himself in regards to the role of Thomas’s ideas in Tolkien’s thought. (Though in his later A Reader’s Guide to The Silmarillion, Kocher goes on to describe the Ainur as desiring Ilúvatar to give the world portrayed in the Vision “full metaphysical Being (in the Thomistic sense).”)