What is natural law, for Aquinas? (ST I-II, q. 94, a. 2)

Summa article explained, no. 4. A paraphrase and reading guide, not a translation.

The short answer. For Aquinas, natural law is "the rational creature's participation of the eternal law": the share in God's ordering reason that human beings have through their own reason. Its first precept is that "good is to be done and pursued, and evil is to be avoided". Other precepts follow our natural inclinations: to preserve life, to goods shared with animals, and to goods proper to reason, like knowing God and living in society.

Where this sits in the Summa

The treatise on law runs from the First Part of the Second Part, question 90, to question 108. Question 91 sorts the kinds of law: eternal, natural, human and divine. Question 94 is about natural law itself. Article 2, "whether the natural law contains several precepts, or only one", is the article most often cited, because it is where Aquinas names the first precept and the inclinations.

The definition comes first, in q. 91, a. 2. Everything subject to divine providence is ruled and measured by the eternal law and so bears its imprint as inclinations to its proper acts and ends. The rational creature is subject to providence in a higher way, because it shares in providence, being provident for itself and others. That participation is the natural law. Aquinas reads Psalm 4:6 this way: "the light of Thy countenance, O Lord, is signed upon us", the light of natural reason by which we tell good from evil.

The objections

1. One law, one precept. A law is a precept. Many precepts would mean many natural laws.
2. One nature. Natural law follows human nature, which is one as a whole. Either there is one precept, or there are as many as the parts of our nature, and then even the appetites would have their own law.
3. One reason. Law belongs to reason, and reason in man is one. So there is one precept.

Sed contra

The precepts of the natural law stand to practical matters as first principles stand to demonstration. There are several first indemonstrable principles. So there are several precepts.

Respondeo

The structure is an analogy between knowing and acting.

Some propositions are self-evident in themselves, because the predicate is contained in the notion of the subject, even if not everyone knows the terms. In speculative reason the first thing grasped is "being", and the first principle built on it is that the same thing cannot be affirmed and denied at the same time.

In practical reason, which is directed to action, the first thing grasped is "good", because every agent acts for an end under the aspect of good. So the first principle of practical reason is that good is what all things seek, and the first precept of law is that good is to be done and pursued, and evil is to be avoided. Everything that practical reason naturally grasps as a human good or evil belongs to natural law as something to be done or avoided.

Because good has the nature of an end, whatever we are naturally inclined to, reason naturally grasps as good. So the order of the precepts follows the order of the inclinations:

1. With all substances, we are inclined to preserve our being. Whatever preserves human life and wards off what threatens it belongs to natural law.
2. With other animals, we are inclined to what "nature has taught to all animals", such as the union of male and female and the education of offspring.
3. As rational, we are inclined to know the truth about God and to live in society. So it belongs to natural law to shun ignorance, to avoid offending those we live among, and the like.

The replies

• To the first. All these precepts make one natural law, because they flow from one first precept.
• To the second. Every inclination of every part of our nature belongs to natural law in so far as it is ruled by reason. The precepts are many in themselves but share one foundation.
• To the third. Reason is one, but it directs everything that concerns us, so whatever reason can rule falls under the law of reason.

The three articles that follow, and why they matter

Readers who stop at article 2 often misreport the theory. The next articles say how far it reaches.

• Same for all? (a. 4). In general principles, yes, and known to all. In details, practical truth can fail, because action deals with contingent things. Goods held in trust should be returned, but not if they are claimed to make war on your own country. The further you go into detail, the more conditions you add and the more exceptions appear. Knowledge can also fail: Aquinas cites Julius Caesar's report that theft was once not considered wrong among the Germans.
• Can it change? (a. 5). It can be added to, by divine and human law. It cannot be subtracted from in its first principles. Its secondary precepts hold in most cases but can fail in rare particular cases.
• Can it be blotted out? (a. 6). The most general principles cannot be blotted out of the human heart in the abstract, though passion can stop us applying them in a particular act. Secondary precepts can be blotted out by bad persuasion or corrupt custom.

How it lines up with the Catechism

The Catechism's account of natural law (CCC 1954-1960) quotes the same tradition. Natural law "expresses the original moral sense which enables man to discern by reason the good and the evil, the truth and the lie" (1954). Its principal precepts are expressed in the Decalogue (1955). It is universal in its precepts (1956), its application "varies greatly" (1957), and it is "immutable and permanent throughout the variations of history", so that even when rejected "it cannot be destroyed or removed from the heart of man" (1958).

Common misreadings

• "Natural means whatever happens in nature." No. The law is called natural because reason, which belongs to human nature, decrees it (compare CCC 1955), not because it copies animal behaviour.
• "Natural law is a list of rules." Aquinas gives one first precept and an order of inclinations. Most moral conclusions are drawn from these by reason, and he says plainly that details can fail.
• "Natural law needs no God." For Aquinas it is a participation in the eternal law. Its precepts can be known by reason, but its force as law comes from the higher reason it shares in.

How to work this article in Aquinian Studio

Put a hard case to it in disputation form: "Whether goods held in trust must always be returned?" Aquinian distinguishes the terms, orders the authorities, gives the strongest objection, and determines with the distinction Aquinas uses in a. 4. Investigate then tests that determination in a second pass. It reasons with authority; it does not become authority, and it is not a confessor. Check named passages against the primary text before formal use. aquinian.com. New accounts start with 150 free credits, no card.

FAQ

How does Aquinas define natural law? As the rational creature's participation in the eternal law: the share in God's ordering reason that human beings have through natural reason (Summa Theologiae I-II, q. 91, a. 2).

What is the first precept of natural law? "Good is to be done and pursued, and evil is to be avoided" (Summa I-II, q. 94, a. 2). Other precepts follow the order of natural inclinations.

Is natural law the same for everyone, according to Aquinas? In its general principles, yes. In matters of detail it can fail, both in what is right and in what people know (Summa I-II, q. 94, a. 4).

Sources

Summa Theologiae I-II, q. 91, a. 2 and q. 94, aa. 2, 4-6, Fathers of the English Dominican Province translation (1920), newadvent.org/summa/2091.htm and 2094.htm. Catechism of the Catholic Church 1954-1960, vatican.va/archive/ENG0015/__P6U.HTM.