In his Epistle to the Romans (2:14-16), Saint Paul affirms that when the Gentiles who do not have the Law—that is, the law revealed by God to the Jewish people—by nature observe the prescriptions of the law, they are a law for themselves, even though they do not have the Law. They show that the demands of the Law are written in their hearts, while their conscience also bears witness and their conflicting thoughts accuse or even defend them, on the day when, according to my gospel, God will judge people’s hidden works through Christ Jesus.
That is natural law: a divine law concerning human conduct or morality, that everyone—Jew or Gentile, believer or non-believer—knows and finds himself bound by. This law enters our minds and urges our wills spontaneously, naturally, whether or not any visible authority codifies or enforces it. Saint Paul was not the first to call attention to it. The Stoic philosophers, with whom Paul was familiar, had already done so. They had also spoken of conscience. This is the judgment of the rightness or wrongness of one’s conduct—past, present or future—in light of the law. Such judgment can be doubtful or even mistaken, because conduct can be a complex matter, and because emotions and bad habits can cloud our minds; but natural law itself is always right and true, and the inner light by which we grasp it is never entirely quenched. Its dictates include such things as the love of God and neighbor, the Golden Rule, and the Ten Commandments.
Fr. Stephen Brock, Ph.D. is a professor of philosophy at Pontifical University of the Holy Cross in Rome and is a visiting faculty of philosophy at the University of Chicago. His research and philosophical interests are mainly the thought of Thomas Aquinas, medieval philosophy, ethics, the philosophy of action, and metaphysics.
Fr. Brock's Recommended Further Reading:
Saint Augustine, On the Free Choice of the Will
C. S. Lewis, The Abolition of Man
J. Budziszewski, Written on the Heart; The Case for Natural Law