Summary: From the texts studied thus far, it is clear that in the Summa theologiae St. Thomas regards the natural law as follows: (1) it is the active participation by the rational creature in God’s eternal law; (2) it pertains to reason insofar as it is something that practical reason constitutes or brings into being; (3) the “something” that practical reason brings into being are “precepts” or practical propositions about what-is-to-be-done, beginning with the “first” or “primary” precept of practical reason, a precept founded upon the concept of the “good.” I now propose to look more closely at the teaching of Thomas in this work on the different sorts of precepts that, taken together, constitute the natural law.
4. ‘Primary’ Precepts of Natural Law, Precepts ‘Close to’ Primary Precepts, and Other Precepts of Natural Law
According to St. Thomas, there are three “grades” or “levels” of natural law precepts. The first grade or set of natural law precepts consists of “those common and first principles,”25 “of which there is no need for any other ‘edition’ inasmuch as they are written in natural reason and are, as it were, self-evidently known (per se nota).”26 Belonging to this set of natural law precepts are principles already examined, namely, the precept that good is to be pursued and done, and its opposite, evil, is to be avoided, such precepts as “man is to avoid ignorance” and “one is not to offend others with whom one must live,” and such like. In addition, as noted above, one can articulate as primary precepts of natural law such principles as life is a good to be preserved and protected, knowledge of the truth is to be pursued, and others of like kind.
Thomas also includes, among the primary and common precepts of natural law, such precepts as “evil is to be done to no one,”27 “do unto others as you would have them do unto you; do not do unto others as you would not have them do unto you,”28 and “you are to love the Lord your God and you are to love your neighbor.”29 And one loves one’s neighbor by willing that the goods of human existence, of which we have already spoken, flourish in him.
Among the first, nondemonstrable principles or precepts of natural law, some direct us to do and pursue the good and avoid its contrary (e.g., good is to be done and pursued and its opposite, evil, is to be avoided, and, as suggested above, such principles as human life is a good to be preserved and protected, knowledge of the truth is a good to be pursued, ignorance is to be avoided, etc.), whereas others concern our way of pursuing such goods (e.g., we are to do so by acting fairly [the Golden Rule], by refusing to do evil to anyone, and by loving God and neighbor). In fact, St. Thomas affirms that the precept to love God and neighbor is precisely the precept or principle from which those precepts that make up the second grade or set of natural law precepts are derived, or in whose light these precepts are known to be true.30
This second grade or set of natural law precepts includes those “that the natural reason of every man immediately and of itself (per se) judges to be done or not done.”31 Such precepts are proximate conclusions from the first nondemonstrable precepts of natural law,32 and they can be understood to be true “immediately, with a modicum of consideration.”33 They are “more determinate” than the primary precepts of natural law, but they can be easily grasped by the intelligence of the most ordinary individual.34 These precepts, which are proximate conclusions from the primary principles of natural law, “are absolutely of the natural law.”35 These precepts, it is true, can become perverted in a few instances because of sin and bad habits, and it is for this reason that they have need of a further “edition,” namely, through the divine (positive) law,36 for these precepts are those that we find in the Decalogue.
The third grade or set of natural law precepts, according to Thomas, are truths about human action that are known only “by the more subtle consideration of reason.”37 They are like conclusions derived from the second set of natural law precepts,38 and they are known only by the “wise,” i.e., for Aquinas, by those in whom the virtue of prudence is perfected. To know these precepts of natural law, “much consideration of different circumstances” is required, and to consider these diligently is something that pertains to the wise. Those not perfected in virtue need to be instructed in these precepts by those who are wise.39
Thus, according to Thomas, there is a definite structure to the natural law. It consists of (1) certain fundamental, nondemonstrable, primary principles; (2) normative precepts that flow immediately, and with very little consideration, from these primary precepts; and (3) normative precepts that can be known only after considerable thought and only by the wise, or those perfected in the virtue of prudence.
This structure of natural law is brought out in several passages of the Summa theologiae.40 One of the most striking is 1-2, q. 100, a. 3, where Thomas asks whether all the moral precepts of the old law can be reduced to the ten precepts of the Decalogue. According to Thomas, all the precepts of the Decalogue, while revealed by God, are capable of being known by the exercise of natural human reason — with the exception of the third commandment, regarding the Sabbath, whose determination of a specific day is not knowable by natural reason.41 The precepts of the Decalogue, in other words, belong to natural law. But they are not among the primary precepts of natural law. The following kind of schema shows the structure of natural law as described by Thomas in this question:
Here Thomas explicitly says that there are two kinds of precepts that are distinct from the precepts of the Decalogue. The primary precepts of natural law, since they are self-evidently true, are written in human reason and do not require divine revelation. Also not among the precepts of the Decalogue are those more specific precepts that need considerable thought for their truth to be grasped. Yet both of these kinds of natural law precepts are intimately related to the precepts of the Decalogue. Indeed, Thomas’s argument here is that the Decalogue in some way does “contain” both these kinds of precepts of natural law. Thomas puts it this way:
I believe that by now Thomas’s understanding of natural law should be quite clear. For him, natural law is a “work” of human reason, consisting in an ordered series or set of “precepts.” The first set of natural law precepts embraces the self-evidently true propositions about what-is-to-be-done that are grasped by practical reason. These primary precepts or first principles of natural law include two sorts of precepts. One sort directs us to do and pursue the good and avoid its contrary (and principles logically related to this basic principle direct us to pursue the real goods perfective of us and toward which we are naturally inclined, goods such as life itself, marriage and the education of children, knowledge of the truth etc). The other sort concerns our way of pursuing these goods: we are to do so by acting fairly (the Golden Rule), by loving God and neighbor, by refusing to do evil to anyone. These primary precepts or principles of natural law can never be obliterated from the (developed) human mind. All moral agents are aware of them, for they are written in the human heart.44
The second set or grade of natural law precepts includes those that are “proximate” to the primary principles. They are so close to them, in Thomas’s view, that they can easily be known by everyone, even the simplest person, unless one’s practical reason is perverted by sin or one lives in a perverse society.45 These derivative