Lewis argues that there is such a thing as the “Law of Nature,” the “Law of Human Nature,” or the “Moral Law”. It governs our behavior. Deep down, we all know it exists. This “law” is comparable to the physical laws that govern the physical universe — like the law of gravity or the law of biological systems. This law is very much real — and it governs our every behavior. We also violate this law a lot! We all appeal to this law every time we find ourselves quarreling with other people.
I agree with Lewis. This law really does exist! Whenever someone treats us unfairly, we instinctively protest and demand the person to say sorry, or we point out to him that he is in the wrong, that he shouldn’t do this or that. And, whenever we ourselves commit an act that is wrong, other people are quick to call our attention to it, and we feel inside us guilt.