The recent natural law confabulation has been a lot of fun and very refreshing. There’s so much to be gained from the recovery of natural law, but we need to point out one other very important concept: the jus gentium. This concept, perhaps better known as the “common law of nations,” was important to both Aquinas (ST I–II, q.95, a.2, 4) and Hooker (Laws 1.10.13). And it was so foundational to John Calvin’s legal thought (Inst. 4.20.13-16) that R. J. Rushdoony, the theonomist innovator, had to single it out as “heretical nonsense” (Institutes of Biblical Law, 9). Happily, the majority tradition has felt differently.
In brief, the jus gentium is the positive expression of the natural law among specific cultures and peoples. Where the natural law is, in the words of our own Peter Escalante, a “proprioceptive conatus” (he likes you to have to look it up), the jus gentium is evidence that diverse peoples express that striving in consistent ways with regard to the most basic corollaries and applications of natural law. There is no pretension that the laws of nations are absolutely identical and consistent, but the uniformity is striking.
C.S. Lewis actually gets at this in The Abolition of Man. The natural law is what he calls “the Tao”: “It is the doctrine of objective value, the belief that certain attitudes are really true, and others really false, to the kind of thing the universe is and the kind of things we are” (HarperCollins, 2009, p. 18). The jus gentium, on the other hand, is the appendix, the “Illustrations of The Tao.”
We find that most modern Christian attempts to answer the question “how then shall we live?” usually ignore the jus commune Europaeum and the broader jus gentium, relying on natural law arguments only. But natural law is not positive law, and while natural law guides prudence radically, prudence and statecraft are mediately informed by positive law and custom. Without a real jus, there can be no Christian jurisprudence; and without jurisprudence, no politics.