Thomas Aquinas on the Law of Nations and the Civil Law

Thomas Aquinas distinguishes 5 kinds of law:

  1. Eternal law
  2. Natural law
  3. Human law (laws derived from natural law)
  4. Divine Law (Old and New Testament)
  5. Law of sin (concupiscence derived from original sin)

A friend writes a question about how Thomas Aquinas subdivides “Human Law” into the law of nations and civil law:

St. Thomas Aquinas divides human law into the law of nations and civil law and says that they both derive, in different ways, from the natural law. I was wondering if Aquinas discusses the law of nations in any depth anywhere that you know of. Also, I just looked at his discussion in the Treatise on Law and I do not see how it meets the requirements to be called ‘law’ as Aquinas defines the term. The issue is of relevance to me because I think that what we lawyers call the common law is more like Aquinas’ law of nations than his civil law. The issue had troubled me because it is not clear to me how the common law meets his definition of law.I hope you are doing well.Take care,


My answer:

Dear Josh,

Yes, human law is subdivided into the ius gentium et ius civile (Summa theologiae I-II, q. 95, a. 4). Notice here that Saint Thomas is moving from lex to jus – subtle distinction.

To answer your question:

(less likely) perhaps jus cannot be stretched to fit lex (I doubt this because in other places Thomas uses jus and lex interchangeably)


(more likely) I think both ius gentium et ius civile do fit the fourfold definition of lex: rational, common good, promulgated, by proper authority.

My real suspicion (just reading that article) is that Thomas finds Isidore of Seville’s ius gentium et ius civile tedious and Thomas is just tidying up that objection before moving on.

Thomas never mentions ius gentium outside the Summa Th. However, he mentions ius civile several times outside the Summa Th – in particular when discussing usury and positive law in De malo, q. 13 a. 4 arg. 6.



PS: For more on natural law and human law, see my short book: Thomas Aquinas in 50 Pages.

Thomas in 50 Boxshot Cover 165 no background

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