Human Nature is the Basis for Morality

There are two very different ideas in the world today about the basis for morality. The typically modern idea is that moral laws are man-made rules like the rules of a game such as tennis, created by human will and therefore changeable by human will. The traditional idea, on the other hand, which is taught not only by the Catholic Church but by all the world's major religions and nearly all pre-modern philosophies, is that the laws of morality are not rules that we make but principles that we discover, like the laws of a science such as anatomy. They are based on human nature, and human nature is essentially unchanging; and therefore the laws of morality are also essentially unchanging, like the laws of anatomy... There are universal principles, based on human nature, for bodily health and for mental health -- and also for moral health.

Because our human nature is composed of body and soul, with powers of intellect, will, and feelings, and because it is our nature to love the good but also to be tempted by evil, it is necessary for us to cultivate such virtues as self-control, wisdom, courage, and honesty. Catholic morality follows the classic Greek philosophers Socrates, Plato, and Aristotle in deriving the essential principles of morality from unchanging human nature and its real, objective needs rather than from the changing subjective feelings and desires of individuals or societies. Thus its essential principles are universal (the same for everyone), objective (discovered, not invented), and unchangeable.

Catholic Christianity:A Complete Catechism of Catholic Beliefs based on the Catechism of the Catholic Church by Peter Kreeft