Have you ever had the experience of reading a book and wished for the life of you that you had a chance to ask the author a few key questions about that book?

It happened to me recently and on a very important subject, the natural law. Before I drop the other shoe, let me say that I’ve been fairly fascinated by the natural law every since I first learned of it and then witnessed it being mocked (but not refuted). I have a chapter in my book Sex Au Naturel: What It Is and Why It’s Good For Your Marriage on the natural law, which is the foundation on which Pope Paul VI built his 1968 Encyclical against contraception, Humanae Vitae (“Of Human Life”).

Now I don’t happen to think that Humanae Vitae is the best-argued papal document in history. (It’s certainly not Paul VI’s best, which I regard as Mysterium Fidei, the encyclical on the Eucharist he wrote four months before the Second Vatican Council ended.) But it is authoritative, and it is binding on Catholics because its norms are taught infallibly through the ordinary magisterium.

What’s striking about the document is the explicit source of authority invoked by Paul VI — an appeal to the church’s competence to interpret the “natural moral law.” He gets right to it near the start of his text (emphasis mine):

No member of the faithful could possibly deny that the Church is competent in her magisterium to interpret the natural moral law. It is in fact indisputable, as Our predecessors have many times declared, that Jesus Christ, when He communicated His divine power to Peter and the other Apostles and sent them to teach all nations His commandments, constituted them as the authentic guardians and interpreters of the whole moral law, not only, that is, of the law of the Gospel but also of the natural law. For the natural law, too, declares the will of God, and its faithful observance is necessary for men's eternal salvation. (HV #4)

So the Church’s competence extends not just to preaching the gospel or interpreting the morality of the Bible, but to properly interpreting the natural moral law, which he later simply calls the natural law. Upon our obedience to the natural law depends our salvation.

In his great Summa Theologiae St. Thomas Aquinas gives us a simple definition: natural law is “nothing else than the rational creature's participation in the eternal law” (I-II.94). God makes man in a particular way, in HIs image and likeness, with the innate knowledge of what to do and what to avoid in order to perfect his nature. It's our inner moral-regulator, discernible by our conscience. St. Paul in Romans 2:4-15 assures us that this law is “written on the heart” and that the Gentiles — those who don’t have the revelation of Moses — will be held accountable for their obedience to it. As my friend J. Budziszewski puts it, it’s what we can't not know.

Each one of us must do good and avoid evil if we are to become the persons God made us to be. Not without God’s grace, we must choose our way into our character, and hence our destiny, for good or for ill. Neither dogs nor dolphins can do this. But in man it is universal. Right and wrong are categories everyone, even the most rank materialist, presumes and acts upon every day. Referring to the natural moral law as the Tao in The Abolition of Man, C.S. Lewis showed just how universal it is with many cross-cultural examples of bad behavior that’s punished and good behavior that’s rewarded.

Space here forbids a full account of why contraception is wrong from a natural law perspective (I cover this in my book), but this is a good spot to drop the other shoe: the book I was reading is After the Natural Law: How the Classical Worldview Supports Our Modern Moral and Political Values.

Its author is John Lawrence Hill, a recovering atheist and now professor of law at Indiana University. After the Natural Law is an adventurous ride through the Greeks and Romans, onto the revelation of Christ and the great synthesis wrought by Aquinas, and ending with some sobering thoughts about how the modern world started to go south after the Enlightenment.

I reached out to him, interviewed him, and now you can enjoy the same enlightening conversation about how the natural law lies behind and beneath what we call our morals and our politics. Watch the interview here: www.patrickcoffin.media/show.