Practical Christ: C.C. Lewis’ Proof that we Choose to Follow Christian Tenents not just because we are supposed to, but because they work best.

C. S. Lewis on the Law of Human Nature

According to C. S. Lewis, the law of human nature provides clues about the highest realities. We’ll take a closer look at his case for each of his claims in sequence.

Claim #1: Morality Is Objective and Universal 

Lewis argues that morality is not something people invented, but, rather, is objective and universal—much like scientific claims about the material world. He pushes back against the idea that morals are something we decide for ourselves and are therefore malleable. Instead, he argues, morality is a fixed and universal truth, and we cannot simply declare what is right and wrong based on our own changing whims. He marshals two key pieces of evidence to support his perspective: Morality is objective because societies all have shared moral standards, and morality is universal because these standards remain remarkably consistent across cultures.

Moral Laws Are Objective

Lewis argues that morality is objective by pointing out that people quarrel by appealing to shared moral standards. For example, if someone accuses another of treating them unfairly, the accused will rarely defend themselves by rejecting fairness as a standard. Instead, they assert that their behavior didn’t violate this standard or that their situation merited an exception. These tendencies reveal that societies have widely agreed-upon moral laws. Lewis argues that the widespread adoption of single standards of morality suggests that moral codes are real and not simply invented.

Moral Laws Are Universal

Lewis argues that morality is universal by pointing out that every culture has a standard of conduct that members expect each other to uphold. While specific morals may change between cultures, having morals does not. Consider the similarities to language: While cultures have different words for things, there is no culture without a language. Therefore, people invented words, but no one invented language itself. Similarly, no one invented morality. 

Furthermore, Lewis argues that moral laws across cultures don’t actually vary that much.There are no moral systems that praise selfishness over selflessness, or that celebrate murder as an inherent good. This suggests that not only did no one invent the idea of morality itself, but that no one invented our core moral tenets either.

The Philosophical Tradition of Natural Law Lewis’s arguments about the objective nature of morality places him in a philosophical tradition called natural law, in which right and wrong are part of the natural order of the world. While its origins might be even older, many scholars trace this idea back to Aristotle, who distinguished actions that were “just by law” from those “just by nature”—in other words, morality can, and does, exist independently of human laws. The theologian St. Augustine incorporated natural law into Christian belief. He argued that God inscribed an “eternal law” in our minds through the act of creation. Therefore even non-Christians are able to intuit God’s moral principles. Lewis draws on St. Augustine’s version of natural law theory when he cites the similarity of moral laws across cultures. The theologian Thomas Aquinas built on St. Augustine’s understanding of natural law, arguing that the full extent of the eternal law is known only to God. However, people could come to know more about God’s eternal law by using reason. Though this view stands in tension with the religious belief that morality could only be known through divinely revealed decrees, such as the Ten Commandments, it aligns with Lewis’s arguments that the veracity of Christianity can be deduced through reason.

Claim #2: Morality Is Non-Material

Lewis argues that, in addition to being objective and universal, morality has no material existence. Moral laws are distinct from the material world in that you can’t point to them in the world of things around us or observe them the way you would material phenomena like gravity. Lewis makes three arguments for the non-material nature of morality.

Argument #1: Moral Laws Require Choice 

Lewis argues that moral laws are non-material because, even though they are objective, you still must choose to follow them. This makes them distinct from other objective laws, like those of physics. When the law of gravity compels a skydiver to fall to the ground, they can’t choose to disobey. Lewis asserts that moral laws require choice because every society has people who disobey them. Thus, they’re not automatic like the law of gravity.

Do We Choose to Follow Moral Laws Freely? In arguing that we must choose to follow moral laws, Lewis implicitly stakes out a position on the argument between determinism and free will. Philosophers have debated this issue for millennia across several continents. In general, determinists maintain that humans are not free to choose their own actions, because their actions are determined by other forces such as physiological processes in the brain, social pressures, or—in older cosmologies—fate. On the other hand, defenders of free will highlight the subjective experience of making decisions. They also argue—as Lewis does here, and as we’ll see more of later in this guide—that choice is a precondition for morality, and without free will, morality would lose its meaning. This debate often cleaves along religious lines, with scientific materialists on the side of determinism and religious thinkers on the side of free will. However, there are some interesting exceptions: The atheist philosopher Jean-Paul Sartre argued that humans have complete freedom of choice—whether they want it or not. Meanwhile, a small minority of Christian thinkers have adopted a rare position called hard theological determinism—in which it is impossible for anyone to act against God’s will. Therefore, they contend, we can’t actually choose our own actions.

Argument #2: Moral Laws Cannot Be Observed Through Behavior 

Lewis argues that you can’t tell a society’s moral codes simply by viewing people from the outside: You would be able to tell how people act, but not how they believed they ought to act. Instead, understanding moral codes requires understanding how people think. Therefore, moral laws do not exist in an observable, material sense.