The question – is there a summary of C.S. Lewis’ essay “The Law of Human Nature,” from his larger thesis The Case for Christianity, which was subsequently incorporated en masse into Lewis’ lengthier treatise Mere Christianity, which also includes his essays Christian Behavior and Beyond Personalities originally delivered as radio addresses – might be misleading. “The Law of Human Nature” is only two-and-a-half pages in length and, consequently, would not seem to require further condensing into an even briefer format. That said, Lewis’ discussion on the law of human nature can be summarized as his articulation of the distinctions between the immutable laws of nature, such as those pertaining to physics, and the more pliable laws of human nature, which are subject to vast differences of interpretation and to which any given individual is free to disagree. As Lewis stated in this essay:
“. . .when the older thinkers called the Law of Right and Wrong "the Law of Nature," they really meant the Law of Human Nature. The idea was that, just as all bodies are governed by the law of gravitation and organisms by biological laws, so the creature called man also had his law—with this great difference, that a body could not choose whether it obeyed the law of gravitation or not, but a man could choose either to obey the Law of Human Nature or to disobey it.”
In other words, gravity exists whether we like it or not; a rock will fall to the earth, as will a human being suspended temporarily in midair. Both the rock and the human body are subject to the force of gravity. That is a law of nature. Whether an individual subscribes to a particular school of thought, however, is a product of that individual’s personal history and proclivity for certain interpretations of man-made constructs. Lewis discusses in this context the notion of an universal appeal to what most might consider logical, such as a social contract prohibiting people from discriminating against others on the basis of ethnicity. To most of us, prejudicial treatment of others because of their ethnicity is morally wrong. That, however, does not mean everyone agrees that it is wrong. The law of human nature, therefore, differs markedly from the Law of Nature.
This, then, is the summary of Lewis’ section titled “The Law of Human Nature.”