Mere Morality and the Cardinal Virtues in CS Lewis’ Mere Christianity: Prudence, Temperance, and Justice

C.S. Lewis’s Mere Christianity (originally a series of BBC radio talks during World War II) presents a defense of core Christian beliefs, …

….including a moral framework that draws heavily on classical philosophy. While Lewis doesn’t explicitly cite Aristotle throughout the book, his treatment of ethics—particularly in Book III, “Christian Behaviour”—shows clear parallels to Aristotelian virtue ethics, as outlined in works like the Nicomachean Ethics. Both emphasize the cultivation of character through habitual practice of virtues, aiming for human flourishing (what Aristotle calls eudaimonia, or a well-lived life). Lewis uses this as a bridge between natural morality (accessible to all humans) and distinctly Christian ethics.

Key Connections: The Cardinal Virtues

Lewis begins his exploration of Christian morality not with the theological virtues (faith, hope, and charity) but with the four “cardinal virtues”—prudence, temperance, justice, and fortitude—which originate from classical thinkers like Plato (in The Republic) and Aristotle. He notes that “cardinal” comes from the Latin for “hinge,” meaning these virtues are foundational, upon which other moral actions pivot. This mirrors Aristotle’s focus on these same virtues as essential for ethical living, developed through reason and practice rather than rigid rules.

Here’s a breakdown of how Lewis describes each virtue in Mere Christianity, with Aristotelian parallels:

• Prudence (Practical Wisdom): Lewis defines it as “practical common sense” or taking the trouble to think through one’s actions. He criticizes the modern dismissal of prudence as mere cleverness, insisting Christians must use their intellect fully. Aristotle, in Nicomachean Ethics, calls prudence (phronesis) the intellectual virtue that guides all others, enabling one to deliberate well about the good life. Both see it as essential for navigating moral complexities, not just theoretical knowledge.
• Temperance (Moderation): For Lewis, this means “going the right length and no further” in pleasures, like food or drink, without turning them into idols. It’s not abstinence but balanced enjoyment to maintain sanity and order loves rightly. Aristotle views temperance (sophrosyne) similarly—as the mean between excess and deficiency in bodily pleasures, crucial for self-control and overall virtue.
• Justice (Fairness): Lewis expands it beyond legal fairness to include honesty, promise-keeping, and truth-telling, aligning it with “righteousness.” He directly nods to Aristotle by summarizing his distinction between universal justice (overall virtue) and particular justice (equitable dealings). In Aristotle, justice (dikaiosyne) is the complete virtue, involving fairness in distributions and rectifications, and it’s habitual— we become just by performing just acts.
• Fortitude (Courage): Lewis describes it as bravery in facing danger or enduring pain, necessary to sustain the other virtues over time. Aristotle agrees, defining courage (andreia) as the mean between rashness and cowardice, especially in the face of death or hardship, and it’s vital for ethical consistency.

Lewis argues these virtues are universal—recognized across cultures as part of the “moral law” he introduces in Book I—and provide common ground for discussing ethics with non-believers. This echoes Aristotle’s naturalistic approach: virtues are innate potentials honed by habit, leading to a flourishing life.

Broader Ethical Parallels

• Habituation and Character Formation: A core Aristotelian idea is that virtues aren’t innate but developed through repeated actions—”we become builders by building.” Lewis adopts this in Christian terms: even if you start with wrong motives, practicing virtuous acts (like loving your neighbor) can transform your character over time. He warns that right actions done for wrong reasons don’t build true virtue, aligning with Aristotle’s emphasis on proper motivation.
• Moral Law and Natural Ethics: In Book I, Lewis’s “argument from morality” posits a universal sense of right and wrong, akin to Aristotle’s view of humans as rational animals with an inherent telos (purpose) toward the good. Lewis sees this as evidence for God, while Aristotle grounds it in nature, but both reject relativism.
• Eudaimonia and Christian Flourishing: Aristotle’s ethics aim at happiness through virtue. Lewis Christianizes this: true fulfillment comes from aligning with God’s design, but he borrows the structure to show how virtues lead to a “good infection” of Christ-like character.

Lewis wasn’t inventing anew; he drew from medieval thinkers like Aquinas, who integrated Aristotle into Christianity. This makes Mere Christianity a modern synthesis, using Aristotelian tools to make Christianity accessible and rational. If you’re interested in specific excerpts or further comparisons (e.g., on the Trinity or evil), let me know!