Читать книгу An Introduction To Moral Theology, 2nd Edition - William May - Страница 12

CHAPTER THREE

The Natural Law and Moral Life

Introduction

Vatican Council II, as we have already seen, taught that the “highest norm of human life is God’s divine law — eternal, objective, universal — whereby God orders, directs, and governs the entire universe and all the ways of the human community according to a plan conceived in wisdom and in love.” In addition, it held that “man has been made by God to participate in this law, with the result that, under the gentle disposition of divine providence, he can come to perceive ever increasingly the unchanging truth” (Dignitatis humanae, no. 3). Man’s participation in God’s divine and eternal law is precisely what the Catholic theological tradition understands by “natural law,” the law that he discovers “deep within his conscience” (Gaudium et spes, no. 16). Although they did not use the expression “natural law” to designate man’s participation in God’s divine and eternal law in these passages from Dignitatis humanae and Gaudium et spes, the Council Fathers clearly had the natural law in mind, for right after saying that “man has been made by God to participate in this law,” they explicitly referred to three texts of St. Thomas; and of these one was obviously uppermost in their mind, for in it Aquinas affirms that all human beings know the immutable truth of the eternal law at least to this extent, that they know the universal principles of the natural law.¹

But what is the natural law? I propose that we begin our investigation of this topic by examining the teaching of St. Thomas on the natural law. We shall then examine the teaching of Vatican Council II, the teaching of Pope John Paul II, and the thought of some contemporary writers who seek to build on the foundations established by St. Thomas. We will consider at length the natural law position developed by Germain Grisez, John Finnis, and Joseph Boyle, taking into account Grisez’s latest views (pp. 110-111), and briefly summarize the theory set forth by Martin Rhonheimer.

NATURAL LAW IN ST. THOMAS AQUINAS

St. Thomas considered the subject of natural law formally in his Summa theologiae, but references to natural law and to such allied notions as conscience, synderesis, providence, as well as eternal and divine law are found throughout his writings, from his early “Commentary” or Scriptum on Peter Lombard’s Libri Sententiarum onward.²

In his master work, the Summa theologiae, Thomas discusses law in general, the different kinds of law (including natural law), and God’s eternal law before offering a more extensive exposition of his ideas about natural law and its relationship both to human positive law and the law of God as divinely revealed. Since natural law is “law” in a real and proper sense, it is important to begin our consideration of Thomas’s thought on natural law in the Summa theologiae by briefly summarizing his teaching on the meaning of law as such. I then propose to note succinctly his understanding of God’s eternal law. I will then turn to a consideration of his more detailed presentation of natural law.

1. The Basic Understanding of Law in the Summa Theologiae

In this work, Thomas begins by saying that law is an extrinsic principle of human acts, in distinction to virtues and vices, which are intrinsic principles of such acts. He initially describes law as “a rule or measure of acts whereby one is induced to act or is restrained from acting.” Since this is so, he says that law pertains to reason, insofar as “reason, which is the first principle of human acts, is the rule and measure of human acts.”³ Law as such is thus something that is brought into being by reason: it is an ordinatio rationis, an ordering of reason. In an enlightening response to an objection that law cannot pertain to reason because St. Paul had spoken of a “law” in his “members” (Rom 7:23), Thomas notes that law can be said to be “in” something or “pertain to” something in two ways: “In one way [law is said to be ‘in’ something] as it is in that which rules and measures. And because this is proper to reason, it follows that in this way law exists exclusively in reason.” He continues by saying that law can be said to be “in” something in a more passive, participative way, in whatever is ruled and measured by a law: “And it is in this way that law is ‘in’ all those things that are inclined toward something in virtue of some law, not essentially, but as it were in a participative sense.”⁴

The fact that law belongs essentially and formally to reason and is, indeed, the result of an act of intelligence is made even clearer by St. Thomas in a response that he gives to another objection. According to this objection, law cannot belong to reason since it can be neither the power of reason itself nor one of its habits or faculties, nor one of its acts. In replying to this objection, St. Thomas says that practical reason — i.e., reason as ordered to action — brings into being “universal propositions directed to action.” These universal propositions of practical reason play a role in practical thinking comparable to the role played in speculative inquiry by the universally true propositions of speculative reason relative to the conclusions that it reaches. And, Aquinas continues, “universal propositions of this kind, namely, of the practical reason as ordered to actions, have the meaning of law” (et huiusmodi propositiones universales rationis practicae ordinatae ad actiones habent rationem legis).⁵

From all this, it is luminously clear that in the mind of St. Thomas law as such not only belongs to reason but consists of true propositions or precepts brought into being by reason.

In subsequent articles of the Summa theologiae (1-2, 90), Thomas describes other qualities of law in the general sense. It must be ordered to the common good,⁶ it must come from the whole people or from someone having charge of the whole people and acting on their behalf,⁷ and it must be promulgated or made known.⁸

2. Eternal Law

Thomas taught that all creation — the cosmos and all things within it — is under the governance of God’s intelligence. Thus, the eternal law is the ratio or divine plan of the governance of all things insofar as this ratio or divine plan exists within the mind of God himself as the ruler of the universe.⁹ The eternal law directs the entire created universe and the activity of all created things, including the activity of human persons. Eternal law is thus the “ratio of the divine wisdom insofar as it is directive of all acts and movements.”¹⁰ The end to which the eternal law directs all of creation is the universal common good of the entire created universe, and it is promulgated along with creation.¹¹

3. Natural Law: Its Central Meaning and Character

Thomas teaches that all created realities “participate” in the eternal law. But they do so differently, in accordance with their natures. Nonrational beings participate in the eternal law in a purely passive way insofar as from it they receive an “impression” whereby “they have inclinations toward their proper acts and ends.”¹² The eternal law is “in” them inasmuch as they are ruled and measured by it.¹³ But human persons, inasmuch as they are intelligent, rational creatures, participate actively in the eternal law, and their active, intelligent participation is precisely what the natural law is.¹⁴ The eternal law is “in” them both because they are ruled and measured by it and because they actively rule and measure their own acts in accordance with it. It is thus “in” them properly and formally as “law.” Contrasting the different ways in which nonrational and rational creatures participate in God’s eternal law, Aquinas says: “Even nonrational animals participate in the eternal ratio in their own way, just as does the rational creature. But because the rational creature participates in it by intelligence and reason (intellectualiter et rationaliter), therefore the participation of the eternal law in the rational creature is properly called law: for law is something pertaining to reason.… But in the nonrational creature it is not participated in rationally; hence it cannot be said to be law [in the nonrational creature] except by way of a similitude.”¹⁵

Natural law, as it exists in the rational creature, is entitatively distinct from the eternal law that exists in God, the superintelligent Creator. But it is not something “other than” the eternal law. It is this eternal law itself mediated to or shared by the rational creature.¹⁶ Natural law characterizes both the nobility of the rational creature as the being created in the image of God and the great love that God has for the rational creature, whom he wills to share actively in his own provident wisdom.

Thomas clarifies the way that the eternal law is “in” the rational creature when he considers the position, held by many of his medieval predecessors, that the natural law is a power or a habit, in particular the habit of synderesis or of the first principles of practical reasoning.¹⁷ He grants that natural law may, in a secondary and derived sense, be regarded as a habit insofar as the judgments of practical reason that together go to constitute it are habitually kept in mind. But in its proper sense, natural law is not a habit, nor is it a power. Rather, it is a reality brought into being (constitutum) through reason; it is a work of human intelligence as ordered to action (ratio practica), just as a proposition of the speculative intellect is an achievement of human intelligence as ordered to knowing for the sake of knowing. Natural law, therefore, is something that we ourselves naturally bring into being by the spontaneous exercise of our own intelligence as ordered to action. It is something that we bring into being by our doing (what Thomas calls a quod quis agit), not something enabling us to bring something into being by our own doing (what he calls a quo quis agit).¹⁸

As such and properly, then, natural law is for St. Thomas an achievement of practical reason. It consists of a body or ordered set of true propositions formed by practical reason about what-is-to-be-done.¹⁹ But what are these propositions, and how do they constitute an ordered set?

Thomas begins to address this issue in the important second article of question 94 of the Prima Secundae of his Summa theologiae. In this article, he is concerned with the “starting points” or “first principles” of natural law, the first set of practical propositions or precepts that go to make it up. In this article, he begins by making an important analogy between the precepts of natural law, which pertain to reason as ordered to action (ratio practica), and the first principles of demonstration, which pertain to reason as ordered to speculative inquiry or knowledge for the sake of knowledge (ratio speculativa). He says that just as being is the first thing that our intellect grasps with regard to its knowledge of reality, so good is what is first of all grasped by our intelligence as directed to action. He then declares: “Therefore, the first principle in practical reason is that which is founded upon the meaning (ratio) of the good, which meaning is, the good is that which all things desire. Therefore, this is the first precept of [natural] law, namely, that good is to be done and pursued, and evil is to be avoided. And upon this [precept or ‘proposition’ of practical reason] are based all other precepts of natural law, namely, that all those things belong to natural law that practical reason naturally grasps as goods to be done [or evils to be avoided].”²⁰

Continuing, Thomas says that “good” has the meaning of an end, whereas “bad” has the opposite meaning. It thus follows that “reason naturally apprehends as goods, and consequently to be pursued in action, all those things to which man has a natural inclination, and things contrary to them [reason naturally apprehends] as evils to be avoided.”²¹

It is most important here to note that Thomas does not say that these “natural inclinations” constitute natural law. Rather, he is saying that the real goods of human existence to which human beings are naturally oriented are grasped “naturally” — i.e., nondiscursively — by human reason as the “good” that is to be done and pursued. Practical reason apprehends in these goods the “ends” or “points” of human choices and action. To put matters another way, the basic practical principle that good is to be done and pursued, and that its opposite, evil, is to be avoided is specified by identifying real goods of human persons. According to Thomas, there exist within us “natural inclinations” dynamically directing us toward specific aspects of human well-being and flourishing, and our practical intelligence “naturally” apprehends as good, and therefore to be pursued in human choice and action, the realities to which these natural inclinations direct us. When he says that practical reason “naturally” apprehends the goods to which human beings are naturally inclined, Thomas means that there is no need for discursive, syllogistic reasoning in order for us to know them as good. Knowledge of these goods is not innate, but it is direct and nondiscursive, given human experience.

But what are our “natural inclinations” and the basic human goods or aspects of human well-being corresponding to them? In q. 94, a. 2, Thomas distinguishes three levels of basic, natural inclinations and basic human goods. On the first level, there is in us a natural inclination to the good in accordance with the nature that we have in common with all substances. The good to which we are naturally inclined at this level is that of being itself, and since, as Thomas elsewhere notes, the being of living things is life itself,²² the relevant human good here is life itself. At another level, there is in us a natural inclination “to more special goods according to the nature” we have “in common with other animals.” The relevant good here is the union of male and female and the handing on of new life and the education of human persons. Finally, there is in us, Thomas says, an “inclination to the good according to the nature of reason, which is a nature proper to man: thus man has a natural inclination to know the truth about God, and to live in society; and in this respect whatever pertains to this inclination belongs to natural law, for example, that man avoid ignorance, that he not give offense to others with whom he must live (conversari), and other such things.”²³ In other words, the relevant human goods to which this inclination points us are such goods as knowledge about God, fellowship and friendship with other persons, and the like.

The list of basic human goods given by Thomas in this article is not intended by him to be taxative or exhaustive; it is rather an illustrative list, as is indicated by the fact that he uses such expressions as “and the like” (et similia) and “of this kind” (huiusmodi) in speaking about the goods that he names. Moreover, in the very next article Thomas explicitly says that “there is a natural inclination in every human being to act in accord with reason. And this is to act in accord with virtue.” Thus, here the good to which we are naturally inclined is the good of virtue.²⁴

It seems that one can legitimately say, on the basis of q. 94, a. 2 of the Prima Secundae, that the goods to which we are naturally inclined, when grasped by practical reason, serve as starting points or principles of practical reason, of natural law, of deliberating about what-is-to-be-done, and that these primary principles could be articulated as: life is a good to be preserved and protected; marriage and the education of children are goods to be pursued; knowledge of the truth, particularly the truth about God, is a good to be pursued; etc. Such principles or precepts specify the basic precept — good is to be done and pursued and its opposite, evil, avoided — by identifying the goods that are to be pursued in action. Surprisingly, however, Thomas himself does not articulate primary precepts of natural law in this way. Rather, in the body of q. 94, a. 2, he articulates precepts such as “man is to avoid ignorance” (homo ignorantiam vitet) and “one is not to offend others with whom one must live” (alios non offendat cum quibus debet conversari).

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 but easily known (according to Aquinas) precepts of natural law are the moral precepts of the Decalogue. According to Aquinas, these natural law precepts are moral absolutes, exceptionless norms, from which not even God can grant a dispensation.⁴⁶

Finally, the third set or grade of natural law precepts includes more remote moral norms, derived from the precepts of the Decalogue as from their principles, and known only after much consideration by the “wise” — i.e., persons perfected in the virtue of prudence or, in Christian terms, saints.

This is clearly the structure of natural law according to St. Thomas.

EXCURSUS 1: St. Thomas and Ulpian’s Definition of Natural Law

Ulpian, a second-century Roman lawyer, defined natural law as “that which nature has taught all animals.” Several contemporary Catholic moral theologians — among them Charles E. Curran, Timothy E. O’Connell, and Richard M. Gula — claim that the teaching of St. Thomas on natural law is highly ambiguous. On the one hand, it stresses the role that reason has to play in constituting natural law. On the other hand, they say, his thought, because of the influence of Ulpian, definitely tends “to identify the demands of natural law with physical and biological processes”⁴⁷ and leads to what they consider a “physicalistic” understanding of natural law.⁴⁸ Because of this claim by some contemporary Catholic theologians, it will be worthwhile to examine the way in which Aquinas accommodated Ulpian’s definition of natural law into his own thought.

In one of his earliest writings, his Scriptum super IV Libros Sententiarum, Thomas takes up the question of natural law in connection with his discussion of a problem that had plagued his predecessors in their attempts to relate natural law to the teaching of Scripture. How could the polygyny of the Old Testament patriarchs be reconciled with natural law?⁴⁹ My concern is not with this specific problem but rather with Thomas’s thought on natural law and his use of Ulpian’s definition of natural law.

In his analysis of this issue, Thomas first notes that all beings have within themselves, by their very nature, principles whereby they can not only bring about the actions proper to themselves but also direct them to their proper ends. Beings that lack knowledge act in a necessary way, but in beings that have knowledge, the principles of operation are knowledge and appetite. In beings capable of knowledge, consequently, there must be a natural concept (naturalis conceptio) in the cognitive faculty and a natural inclination (naturalis inclinatio) in the appetitive faculty, whereby these beings are ordered to the actions and ends appropriate to them. Since man differs radically in kind from other animals, however, in his ability to know the end as such and the relationship of means to ends, the “natural concept” in his case “is called natural law, whereas in other animals it is called a natural estimation (aestimatio).” Nonrational animals “are impelled by a force of nature to perform actions proper to them rather than acting by being regulated, as it were, by any kind of judgment properly so called.” Aquinas then continues: “Therefore natural law is nothing other than the concept naturally impressed upon man whereby he is directed to acting suitably in the actions that are proper to him, whether these actions pertain to his generic nature, such as generating life, eating, and so forth, or whether they pertain to his specific nature as man, such as thinking and things of this kind.”⁵⁰

What is most important about the notion of natural law expressed in this passage from an early writing of St. Thomas is that natural law is explicitly related to human intelligence, to the fact that the human person, alone of all animals, is capable of knowing the end as such and of relating means to ends. The thought expressed here and elsewhere in St. Thomas’s Commentary on the Sentences is surely in accord with the thought set forth in the passages from the Summa theologiae that we have already considered: natural law, as law, is exclusively proper to human persons, and, precisely as law, natural law is related to human cognition.

As already noted, the discussion of natural law in this passage from the Commentary on the Sentences was prompted by the polygyny of the patriarchs. The question posed was “whether having many wives is contrary to natural law.” In the body of the article, from which the citations given above are taken, Thomas asserts that polygyny is indeed against the natural law in the sense that it impedes at least partially the marital good of fidelity and the peace and harmony that ought to reign in the family. He also notes that it completely destroys the good of the “sacrament” of marriage. He concedes, however, that it is not destructive of the principal end of the institution of marriage — namely, the procreation and education of children — and in this sense is not against natural law.⁵¹ One of the objections to the view (which Thomas held) that polygyny is against natural law had urged that a plurality of wives is in no way against natural law, inasmuch as the natural law is that which nature has taught all animals — i.e., Ulpian’s definition of natural law — and obviously in the animal kingdom it is by no means unnatural for one male to have more than one mate. In replying to this objection, Thomas distinguishes several ways in which natural law could be understood; and in commenting on these ways of understanding natural law, Thomas takes up the celebrated definition of Ulpian.

Thomas says that natural law can be understood, first, to refer to something that is natural by reason of its principle or source. It is in this way that Cicero understood natural law, for to him it was a kind of innate source or power, a principle intrinsic to things (ius naturae est quod non opinio genuit, sed quaedam innata vis inseruit). He goes on to note that the principle from which natural law springs can be extrinsic to the being regulated by natural law, and in this sense he makes room for the definition given by Gratian (incorrectly attributed, in Thomas’s text, to Isidore), that natural law is what is contained in law and gospel (ius naturale est quod in lege et in Evangelio continetur). Finally, he notes that natural law may be understood to refer to what is natural, not by reason of its source or principle but rather by reason of “nature,” i.e., by reason of the subject matter with which natural law is concerned (tertio dicitur ius naturale non solum a principio, sed a natura, quia de naturalibus est). If natural law is taken in this sense, nature is contrasted with or is opposed to reason. Consequently, “taking natural law in its most restricted or limited sense” (strictissimo modo accipiendi ius naturale),⁵² “those things that pertain only to men, although they follow from the dictate of reason, are not said to be of the natural law; but only those things that natural reason dictates about matters that are common to man and to other animals; and thus the aforesaid definition is given, namely, that ‘natural law is what nature has taught all animals.’ ”⁵³

It is most important to be clear about Aquinas’s thought here. He is definitely not claiming that natural law, as law, is something infrarational, an instinct that human persons share with other animals. After all, in the body of the article he had stressed that natural law as such is unique to human beings and that it is a naturalis conceptio. In nonrational animals, he taught in the body of the article, there is no natural law; there is only a natural “estimation,” a power or force of nature impelling them to act in ways appropriate to achieve the ends for which they are made. Thus, in this celebrated passage, Thomas in no way repudiates what he has just said in the body of the article (or what he was to say subsequently in the texts from the Summa theologiae that we have already examined) about natural law as something brought into being or constituted by reason. He is making room for Ulpian’s understanding of natural law in only a limited way, namely, in the sense that it refers to the subject matter with which or about which natural law is concerned, for this is what he explicitly says. In other words, he is saying that the tendencies that human beings share with other animals are fitting objects of natural law taken in its proper sense as an achievement of reason — they are fit matter to be brought under the rule of law, i.e., under natural law understood as an achievement of human reason. This is evident from the text, for Thomas explicitly says that the natural law, understood in Ulpian’s sense, has to do only with those things that “natural reason dictates about matters that are common to man and to other animals” (illa tantum quae naturalis ratio dictat de his quae sunt homini aliisque communia).

Thomas also makes room for Ulpian’s definition in his later works, in passages in the Summa theologiae⁵⁴ and in his commentary on Aristotle’s Nicomachean Ethics.⁵⁵ But in all these places, the room given by Thomas to Ulpian’s definition of natural law as the law that nature has taught all animals is limited to fit in with his own teaching on natural law as the work of reason. Natural law as defined by Ulpian never has the meaning of an ordinatio or dictamen rationis, the achievement of practical reason, that Thomas always considers to be the essential element of law and of natural law in the formal, proper sense.⁵⁶ Ulpian’s definition can never be used in reference to natural law as that which is in something as ruling and measuring. It uniformly refers to natural law only in an accommodated sense, as found in something only “participatively, as it were.”⁵⁷ In short, Ulpian’s definition of natural law, as St. Thomas appropriates it, refers to the tendencies or inclinations that human beings possess by virtue of being, in truth, animals, albeit animals of a special and unique kind — tendencies that can be grasped by practical reason along with the real goods toward which they incline the human person, and thereby formally brought under the dominion of reason and capable of being expressed in principles or propositions that serve as starting points for thinking about what is to be done in and through human action — that serve, in other words, as the principles that go to make up the content of natural law as law.⁵⁸

There was good reason, I believe, why Thomas took pains to make room for Ulpian’s definition of natural law within his thought. Aquinas was no dualist. For him, a human being is not an incarnate spirit, a “separated substance” in some way accidentally united to a material body. For him, a human being is first and foremost an animal, a very special kind of animal to be sure, different in kind from all other animals by reason of his intelligence and power to determine his life by his own free choices, but an animal nonetheless. Thus, the tendencies that humans possess in virtue of their animality are basic human tendencies, fundamental inclinationes naturales, and the goods correlative to these tendencies, goods such as the procreation and education of children, are basic human goods meriting the respect of human intelligence.

This analysis of the way in which Thomas incorporated Ulpian’s definition of natural law into his own thought on the subject shows that he never accepted Ulpian’s understanding of natural law as a nonrational kind of instinct. Rather, he consistently held that natural law, formally and properly as law, is the work of practical reason. He accepted Ulpian’s definition only as a very restricted or limited way of understanding natural law, as referring to those tendencies that human beings share with other animals and which, in the human animal, must be brought under the rule of reason, under the tutelage of natural law.

EXCURSUS 2: St. Thomas’s Teaching on Natural Law in the Summa Contra Gentes