The Clarity and Specificity of Thomistic Natural Law

Natural law theory has had a long and honorable history – from ancient Greek philosophy to the Stoics, St. Thomas Aquinas and other scholastics, as well as Protestant “natural lawyers” such as Grotius, Cumberland, and Pufendorf.

In the last few centuries, however, an immense amount of opposition to natural law has emerged from ethicists. Jeremy Bentham (1748-1832) complained that appeals to “natural law” were simply camouflaged personal sentiments, and developed his own theory, utilitarianism, as an external gauge that would offer objective moral criteria.

Immanuel Kant (1724-1804) faulted natural law for its lack of authoritativeness, and offered his own procedure for testing for “universal” norms, the “Categorical Imperative,” as a sure guide for rational certainty in moral matters. 

In the latter half of the twentieth century, John Finnis, Germain Grisez, and others have proposed a “new natural law” theory, which is based on seven “self-evident” rational values.

Stephen Buckle in Companion to Ethics (1991) sums up what he considers to be the main problem with natural law: namely, the presupposition that we cannot know enough about human nature to derive moral norms.

More recently, some Catholic magazines have joined the fray in opposition to natural law. The magazine First Things (December 2009) published Paul Griffiths’ “The Nature of Desire,” which argued that the unrealizable “infinity” of human desires depicted by Shakespeare and other artists makes it impossible to portray any human inclinations in terms of a “natural law.”

And in June, 2012, The New Oxford Review published Melinda Selmys’ “Is the Natural Law Obsolete,” which claims that natural law is a “dead letter” unless it is forcefully bolstered with appeals to aesthetics.

A common denominator in the articles by Griffith and Selmys is a complete lack of reference to any natural law theory, except for a single indirect reference by Selmys to Aquinas’ theory. I and others wrote critical letters, which were published a few months later by both magazines, but the authors’ replies to these letters still showed hardly any familiarity with, or interest in, natural law theory.

If we equate natural law merely with what Aquinas calls the “first principle” of natural law – i.e., good is to be done, evil is to be avoided – the world understandably. . .yawns, and goes on its merry way.

But, as Aquinas argues, this apparently single principle of natural law becomes threefold, if we take into account the ontological aspect of natural inclinations. The three “precepts” of the natural law that follow from this basic principle are what give “teeth” and specificity to the natural law, and rescue it from being the merely vague and abstract idea of “conformity to nature,” which elicits dismissal by critics.

          The Triumph of Aquinas (detail, with Aristotle, Plato, and Averroes) by Benozo Gozzoli, c. 1480

A specific characteristic of these precepts, as I argue in my book, Natural Law: an Introduction and Reexamination, is that they are also natural rights; this differentiates them from the multitude of idiosyncratic inclinations that cannot be claimed as universal laws or rights.

A triad of laws/rights follows from an analysis of basic human inclinations: 

1.         The law of self-preservation; which is also the right of self-preservation, and which implies a reciprocity among humans respecting the right to exist. Specific applications of the first precept follow clearly: duties to protect one’s life, not risk life unnecessarily, not commit suicide, work to acquire the property necessary for sustenance, and recognize others’ right to life and property.
2.         The duty to procreate and care for progeny – a care that, because human animals require much more time than other animals to mature, can be required for many years. Obviously included in this precept is the nurturing of infants and children, the teaching of skills for their continuance and success in life, etc. Likewise included is the right of procreation (not “reproductive rights,” the current euphemism for abortion), which is infringed by governmental measures like China’s “one-child” policy. (Aquinas explains that procreation is a duty for the human race as a whole, but not for each individual; so a person may decide to remain single, or may even embrace celibacy in a religious order.)
3.         The third precept is connected with rationality itself: the duty of rational beings in the intellectual/theoretical sphere to seek the truth, and in the practical sphere to work for a rational ordering of society. Clearly this implies a duty and right to educate oneself, and for society to strive to provide the necessary implements for education. Also, it clearly rules out ideological prohibitions that restrict access to the truth, or withhold facts necessary for making rational decisions. One might also add, it implies the duty/right of news media to present “the whole news,” not a truncated, biased version.

The examples I have just mentioned seem to follow without too much ratiocination from the three Thomistic precepts. Aquinas admits, however, that there are some “secondary” applications that may not be clear in some environments or circumstances. He gives examples of cases where different ideas of property rights may seem to legitimize stealing, or where ignorance of normal sexuality may lead to sodomy.

We might add the following extra possibilities of mistaken “secondary applications” caused by circumstantial ignorance:

  • The incredible ignorance of mothers who really think they are just destroying something like a parasite, not a human being, in abortion;
  • the ignorance of users of contraceptive pills who, making use of the complex chemical mechanisms, really think they are doing something virtuous, even helping to combat “overpopulation”;
  • the ignorance of educators who really think they are helping civil society by introducing children to information about all kind of anomalous sexual practices.

But certainly, for most normal rational beings, it should not be very difficult to deduce some very concrete applications from the three precepts of natural law: the law/right of self-preservation; the law/right of “increasing and multiplying”; and the law/right of seeking the truth and combating error both in the intellectual and the practical spheres.


Howard Kainz, Emeritus Professor at Marquette University, is the author of twenty-five books on German philosophy, ethics, political philosophy, and religion, and over a hundred articles in scholarly journals, print magazines, online magazines, and op-eds. He was a recipient of an NEH fellowship for 1977-8, and Fulbright fellowships in Germany for 1980-1 and 1987-8. His website is at Marquette University.