C S Lewis was, I believe, “medieval” in the very warp and woof of his thought. To borrow from Wikipedia, b/c this morning I am lazy, and in this case Wikipedia is accurate:
Lewis then taught as a fellow of Magdalen College, Oxford, for nearly thirty years, from 1925 to 1954, and later was the first Professor of Medieval and Renaissance English at the University of Cambridge and a fellow of Magdalene College, Cambridge. Using this position, he argued that there was no such thing as an English Renaissance. Much of his scholarly work concentrated on the later Middle Ages, especially its use of allegory. His The Allegory of Love (1936) helped reinvigorate the serious study of late medieval narratives like the Roman de la Rose. Lewis wrote several prefaces to old works of literature and poetry, like Layamon’s Brut. His book “A Preface to Paradise Lost” is still one of the most valuable criticisms of that work. His last academic work, The Discarded Image: An Introduction to Medieval and Renaissance Literature (1964), is a summary of the medieval world view, the “discarded image” of the cosmos in his title.
As I have explored in another post, Lewis was in tune with medieval thought as much in his philosophical and ethical thought as in his literary scholarship, his imaginative writings, or his Christian apologetics. What follows are some notes and reflections on James Patrick, “The Heart’s Desire and the Landlord’s Rules: C. S. Lewis as a Moral Philosopher,” in The Pilgrim’s Guide: C. S. Lewis and the Art of Witness, ed. David Mills (Grand Rapids, Eerdmans: 1998):
Before he became a professor of English literature, CSL was “an Oxford graduate looking for a fellowship not in literature or theology but in philosophy.” He tried in 1922 “for a fellowship at Magdalen College,” and “the essay he submitted . . . posed the existence of natural law.”
Unlike postwar ethical theories, “the moral philosophy of the 1920s was not (generally) relativistic. Appeals to history, to the great tradition represented by the Ten Commandments and the twelve tables of Roman law, were not yet ruled out by insistence that nobody could really tell what goodness and virtue might be or by the warning that virtue might mean something different to Estonians and Eskimos.” (71)
Here’s the sequence on what I call his medievalism and then his modern phase (before his conversion to Christianity):
78 “His schoolmaster Kirkpatrick said that Lewis read more classics than any boy he had taught, and E. F. Carritt, the University College don who interviewed him when he applied for admission to Oxford, said that Lewis was the best read applicant he had ever examined. At Oxford he was still the boy of books Kirkpatrick remembered, interested in the past and in the things of creative imagination.” These characteristics–the affinity and respect for past writings and the imaginative bent–I identify as typically medieval.
78 “But the soldier who returned to studies in January 1919, after being wounded on the front, was also hard at work perfecting what  he called in Surprised by Joy his new look, a tough-minded stance that exchanged the romantic longing of his prewar days for the somber, stoical belief that this world, as it is, is all that we will know, so that we ought to bear its deep pains and cherish its moderate joys with as much courage as we can muster. He was an incipient modern, a promising intellectual who wrote poetry of a vaguely pessimistic kind founded upon a philosophy in which the fundamental category was ‘Spirit.’”
79 That post-WWI Lewis became “sympathetic to the new no-nonsense philosophy and to the moral philosophy that accompanied it, the first principle of which was the doubt that objective judgments about value were possible.” Lewis had, for a while, some sympathy to “realism,” defined by Patrick in this essay as “the doctrine that the only things I can really know are things I can see and touch and describe more or less exhaustively,” which “has a way of turning into subjectivism, the idea that there is nothing outside myself that I can really know at all.” (81)
But Lewis would soon become “successively an idealist, a pantheist, a theist, and finally a Christian,” through the steps described in Surprised by Joy and “summarized in the preface to the third edition of The Pilgrim’s Regress.” (81)
79 In 1925 Lewis became a teacher at Magdalen College, “where the most important philosopher was the great idealist John Alexander Smith, who . . . displayed a polite skepticism toward anyone who would propose in 1920 to reject the cumulative moral wisdom of over two thousand years on behalf of any conceivable new theory.” Again, this bias toward the weight of tradition I would identify as quintessentially medieval.
79 “From the time he decided that moral value was real, becoming thereby an ally of . . . the classical school, Lewis made unremitting intellectual war on the utilitarians, the idealists, and the moral subjectivists.” I think it is fair to describe Lewis at that time, and through the rest of his life, as having great essential sympathy for both classical and medieval philosophy, over against modern philosophy, though he was not reactionary or obscurantist, stubbornly ignoring all trends in modern philosophy. Rather, “he also took something from each” of his modern philosophical opponents.
80 “The Abolition of Man attacks moral subjectivism as it was found in the 1940s.”
82 In The Pilgrim’s Regress: An Allegorical Apology for Christianity, Reason, and Romanticism, which Lewis “wrote in a few weeks in 1931, just after his conversion to Christianity,” “the problem that dominates the work is given in its subtitle: the resolution by Christianity of the conflict between the rules delivered by reason and romantic desire rooted universally in imagination.”
83 The “Pilgrim” of the book, John, travelled with an Enlightenment figure, Vertue, who struggled with “the Kantian paradox that teaches that duty must be pursued without self-interest.” In Kantian terms, “desire . . . is morally disqualifying simply because we are doing what we do not simply because it is good but because we wish to do it.”
83 “The resolution of Vertue’s paradox lies in the discovery that the existence of the [moral] rules [by which we live] does not depend on our knowing the Landlord. The rules are not products of our hearts or consciences, though we may grasp them with conscience. Nor are they products of fear or love [the realm of those “rewards” and “self-interest” that Kant eschewed as morally poisonous]. The rules are simply part of the eternal texture of things that we discover.” Could only Christians, then, live morally? No: “though [the rules] may be rooted in the very existence of [God], we need not know [God] to discover them.”
83 “This is a first principle that most moral philosophers of the generation before the Great War would have held in some form, the belief that natural law exists and . . . is in fact the basis off every kind of morality and every civil code until the day before yesterday.”
83 How thoroughly this notion of the natural moral law suffused the medieval period is indicated here: “Aristotle had assumed it, and Plato. Cicero had spoken of it when he called it the law that is not written down. When St. Paul wrote that even the Gentiles knew that certain kinds of behavior were wrong, he was appealing to natural law. This same idea informed the thought of St. Augustine in the fourth century [the towering figure of theology and ethics throughout the early and into the high medieval period] and St. Thomas in the thirteenth [the pinnacle of scholastic theology and philosophy], and influenced Anglicanism at its origin through Richard Hooker’s [scholastically framed] Laws of Ecclesiastical Polity.”
84 In other words, Lewis concluded, as the whole Western medieval tradition, from one end to the other, had assumed, that “natural law is a metaphysical reality.” “In the last essay he wrote for publication, Lewis said of natural law, ‘I hold this conception to be basic to all civilization’ [“We Have No ‘Right to Happiness,’” in God in the Dock (Eerdmans, 1970), p. 318].”
85 How this relates to Christian theology: “Grace does not destroy but perfects our ever present – if, in human terms and with human means, inevitably frustrated – desire for goodness. But it is true that our pursuit of goodness, with all the condemning discomfort that brings, is transformed into love. The rules never disappear, but they are, as Our Lord told us in the great fifth chapter of Matthew, made into matters of the heart. The Landlord, Lewis wrote, will help us keep them.”