"Men ought to be unselfish, ought to be fair. Not that men are unselfish, nor that they like being unselfish, but that they ought to be. The Moral Law, or Law of Human Nature, is not simply a fact about human behaviour in the same way as the Law of Gravitation is...a fact about how heavy objects behave." Lewis shows us in this chapter how the Law of Human Nature is a fact , a reality, about humanity that must be considered."