Introduction to Natural Law Jurisprudence (part 4)

By Professor Brian M. McCall

Adapted from ch. 1 of The Architecture of Law: Rebuilding Law in the Classical Tradition (Notre Dame Press 2018). Part 1 can be found here, part 2 here, and part 3 here.


Combining the elements of Aquinas’s definition and effects of law produces an understanding of law as a rule and measure of human acts ordained by reason toward the common good, which is promulgated by one who has care of the community and which makes use of punishment to make men good by commanding good, forbidding evil, and permitting neutral acts. This definition identifies the genus of law, but when we penetrate deeper we see that law is composed of different species. To help understand these distinctions we can draw upon the image of an architectural structure. Just as a building is composed of many levels, so too the genus of law is composed of several levels of law. Before looking at individual levels, however, it is necessary to survey the design of the overall structure. How do the pieces fit together?

Gratian begins his treatise on laws with the following division of the types of law making up the legal structure: “The human race is ruled by two things: natural law and long-standing human customs.”115 Gratian immediately sheds more light on this two-part division of law in the first causa of this first distinction when he quotes Isidore of Seville:

All the laws that exist are either of divine or human origin. Divine laws are constituted [constant] by nature, but human laws are constituted by human customs, and therefore human laws differ from community to community because certain things are pleasing to different communities. The immutable divine will [fas] is the content of divinely made law, and political or conventional justice [ius] is the content of human law. That is why it is in accordance with divine law [fas] to cross through the field of another person, but it is contrary to human-made law [ius].116

The passage begins with a differently worded two-part division. Whereas the first division was between natural law and custom, the second is between divine law and human law. The terms “divine” or “human” can be reconciled to the earlier division, natural law and custom. The second division refers to their respective origins, whereas the first refers to a representative type of each genus produced by divine or human agency. Huguccio in his commentary on Gratian confirms the divine origin of natural law and verbally links Gratian’s opening division to the passage of Isidore quoted by Gratian.117 He also explains that custom (mos) is human law (jus humanum), which is invented by man.118 Isidore says that divine laws stand in or are based on (constant) nature, whereas human law is based on longstanding practices. Hence, natural law has its origin in God, and custom is the creation of human law. The Ordinary Gloss on this opening passage explains natural law is “divine,” and “custom” is “customary law or written or unwritten human law.”119 Isidore further notes that since human laws are rooted in the customs of nations, they can vary from nation to nation and are not universal. The implication is that divine law, rooted in nature, does not so vary. The divine law is immutable because it has its source in nature, which is universal.

Gratian’s text then introduces yet another pair of words to identify each of these two categories. First it calls laws of divine origin (that which stands in the nature of things) “fas.” This Latin word means that which is “right or fitting or proper according to the will or command of God.”120 Its universality and unchangeable nature is conveyed even by its grammatical status as an indeclinable noun—a noun that, uncharacteristically for Latin, does not change its ending according to its function in a sentence. Huguccio describes fas as whatever is “permitted,” “said to be appropriate and good,” and “ought to be said to be pleasing.”121 As opposed to customs that may please one people but not another, fas ought to be pleasing to all. The text then calls all human laws “jus.” This is a general Latin term often translated as “law,” but as Kenneth Pennington has argued, it conveys a rich penumbrae of meanings beyond mere legal enactments.122 It encompasses the sense of that which is right or just in light of human judgment.123 Justinian’s Digest contains a general definition of jus as that which is “always equitable and good” (semper aequum ac bonum).124 Cicero in a letter to Atticus uses the same construction of fas and jus to refer to everything that is right according both to divine and human reckoning.125 Natural law (jus naturale) and long-standing custom (mos) thus stand in the opening lines of the Decretum as representatives of these two overarching groupings of everything that is right and good, from both the perspective of God (fas, rooted in the nature of things or natural law) and man (jus, rooted in human determinations of what is right or of long-standing customs). Both sides of this coin of what is right and good must be examined to determine a rule and measure for conduct. Man is ruled by both natural law and custom, fas and jus. Gratian gives a specific example to illustrate the need to consult both types of law for a complete answer: human law (lex humana) might prohibit something that could be permissible by divine law (lex divina). Passing through another’s field may be permitted by divine law (fas), but prohibited by human ordinance (ius).

Thus, for a complete understanding of the rule and measure of human action, both groupings of law must be consulted. In this vein, Justinian’s Digest defines jurisprudence (the wisdom of law) as “the knowledge of divine and human things, and the knowledge of justice and injustice.”126 Natural law is a component of a dual system. To understand natural law, one must know it in this context.

As Gratian comments, this two-part division of law is itself subdivided into many species.127 This first category of law identified by Gratian, divine, contains the three types of law, which Aquinas calls eternal law (lex aeterna), natural law (lex naturalis), and divine law (lex divina), the last sometimes referred to as the law of the scriptures (lex scripturae). Each of these types has been promulgated directly by God. Gratian’s second category contains written statutes and long-standing customs, both promulgated by human lawgivers. Each of these species of law is epistemologically and jurisdictionally related to the others. One can understand neither one of these individual species nor the entire concept of law as a whole without understanding the essence of each species. Most contemporary jurisprudence proceeds on the assumption, stated or implied, that either (1) only the species contained under the heading “human law” exist and the others are not real, or (2) if the other species under “divine law” exist, knowledge of them is unnecessary to understanding human law. Classical jurisprudence rejects both assumptions. Simply because the trim carpenter cannot see the foundation or the wall studs does not mean they do not exist. At least some knowledge of the entire edifice is indispensable to anyone who works on or within its walls.

The eternal law is the most general and foundational element of the structure. It contains the definition of all created finite beings. Its precepts, legislated from the foundation of the world, determine the end or perfection of each substance and provide means for the attainment of that end. The eternal law does not directly tell rational creatures how to act. It rather invites rational creatures to participate in the determination of human action by electing means to the end established by eternal law. In this sense, eternal law limits action by limiting the end of human action. The natural law is deeply connected to the eternal law and provides precepts orienting rational beings to their end established by the eternal law. The precepts of natural law provide generally worded principles of action that orient freely chosen human action to the perfection of human nature. Natural law precepts thus rise up out of the eternal law as the frame of a building rises out of the foundation. A frame gives more concrete definition to the structure of a building, which is constrained by the footprint of the foundation. Yet, the frame only generally defines the final appearance of the building. Many more details will determine it. Likewise, the natural law, by identifying hierarchically related ends of various aspects of human nature, provides more direction for electing means to attain the end of human nature. Yet, these precepts of natural law by their very design require further determination or specification, which specification is left to legal authorities, personal superiors, and individual persons, depending upon the nature and effect of the particular action contemplated. Human beings thus participate in making specific laws or rules of action at varying levels depending upon the circumstances. Likewise, artisans and craftsmen add detailed work and decoration to a frame to give the structure its final appearance.

To decorate the legal structure, practitioners of the legal craft must understand the eternal and natural law to know what it is they are decorating. This knowledge is not merely interesting but essential. Even the pagan philosopher Cicero understood that knowledge of these fundamental laws was necessary to the study and practice of law. In De Legibus, which is written as a dialogue, Atticus and Quintus want Cicero to begin discussing the details of the civil laws of Rome. Cicero responds that he cannot start a discourse on law at that point. First the most basic truths about human nature and the purpose of human existence must be understood:

You must understand that there is no subject for discussion in which it can be made so clear what nature has given to humans; what a quantity of wonderful things the human mind embraces; for the sake of performing and fulfilling what function we are born and brought into the world; what serves to unite people; and what natural bond there is among them. Once we have explained these things, we can find the source of laws and of justice.128

Atticus then objects that in this plan of discourse Cicero is departing from the common practice that the understanding of law should be drawn from the “praetor’s edict . . . or from the Twelve Tables.”129 To which Cicero responds:

In this discussion we must embrace the whole subject of universal justice and law, so that what we call “civil law” will be limited to a small and narrow area. We must explain the nature of law, and that needs to be looked for in human nature; we must consider the legislation through which states ought to be governed; and then we must deal with the laws and decrees of peoples as they are composed and written, in which the so-called civil laws of our people will not be left out.130

Cicero understood that the study of law must begin with the most fundamental principles of human nature, which are known through the eternal and natural laws, but contemporary legal scholarship and education in American law schools limit themselves to cataloging, interpreting, and discussing the details of the edicts and other texts of civil law. If Cicero were alive today, he likely would say all of this work needs to follow and be subordinate to a knowledge of these higher laws.

Later Christian philosophers and jurists add to Cicero’s understanding a new font of knowledge. In addition to the eternal and natural law, which all rational creatures can come to know by use of their innate reason, God has promulgated a third type of law, referred to as the “divine law” or the “law of the scriptures.” One of the roles of the precepts of this type of law is to reveal principles of natural law more clearly. In addition to relying on our own, fallible reason to discover these fundamental laws, Gratian and Aquinas argue that we have direct access to them through revelation. Gratian makes this point clear in the opening passage of the Decretum when he introduces the division of law into natural law and long-standing custom. He explains that the natural law is contained in the Law (by which he means the law revealed in the Old Testament) and the Gospels, which he summarizes by quoting the Golden Rule (Matt. 7:12).131

Cicero’s insistence that we must start with cosmological and ontological truths, and later Christian jurists’ insistence that we must consult the divine law, before studying the details of civil laws raises an important question. The classical natural law tradition is rooted in a theological perspective. For the pagan philosophers and jurists this perspective was a vaguely articulated perspective, sometimes pantheist and sometimes a monotheist tendency, that transcended the popular polytheist religions of Greece and Rome. Upon the dawning of Christianity, the perspective shifted to a clearly articulated Christian theology. For Cicero, the eternal and natural laws had their origin in a vague supreme power in the universe. For Gratian and Aquinas, jurisprudence was firmly rooted in the soil of Christian theology, and the origin of all law was more than a cosmic force—it was a personal God who became incarnate to save mankind and make the contents of divinely promulgated law more clearly and widely known.

The question then arises for jurists who are committed to the natural law tradition but are living in a pluralist and largely secular and atheistic world: To what extent is belief in and knowledge of God (either vaguely as for Aristotle and Cicero, or as with the revealed God of the Trinity) a prerequisite to accepting, understanding, and using natural law in legal practice? We can sketch a preliminary answer here.

Scholars such as Michael S. Moore have argued that commitment to natural law jurisprudence is possible without any theological commitments. Unlike Moore, a professed atheist,132 Finnis clearly professes Christianity but argues that although one who accepts Christian revelation may understand the purpose and origin of natural law better than one who does not, Christian revelation and theological commitments are not necessary to come to know natural law or, in the nomenclature of Finnis, the principles of practical reason. Theological truths may be important to Finnis in other contexts, but they are not necessary to articulate his understanding of practical reason. On the other end of the spectrum from the claims of Moore and Finnis, Kai Nielsen has argued that “if there is no God or if we have only the God of the Deist, the classical natural law theory is absurd, for there will then be no providential governing of creation, no plan for man of which the natural law is a part.”133 Although Nielsen is no fan of classical natural law, his reading of Aquinas is more faithful to the Angelic Doctor than that of Finnis. Nielsen rightly sees that Aquinas’s, and hence all classical natural lawyers’, understanding of and justification for natural law is dependent upon specific theological (at least those of natural theology) claims: “For such [Aquinas’s] natural law theory to be justified, God, in fact, must exist; and it must be a further fact that God’s nature is essentially what Aquinas says it is.”134 Although on this point, and not on many others, I agree generally with Nielsen’s claim that at the end of the analysis God and particular aspects of His nature are ultimately indispensable to a complete justification for and understanding of natural law, my own answer, however, does add a nuanced distinction to Nielsen’s claim. The philosophers and jurists of antiquity demonstrate that one can come to know that natural and even eternal law exist and can come to know specific precepts thereof. Thus far, Finnis and Moore are correct that some knowledge of and argument in favor of natural law can be had without specific theological commitments. Yet, I will argue, owing to failures of both the human will and reason, a theologically neutered approach is ultimately incomplete and likely to persist in erroneous conclusions. One who follows the thread of natural law reasoning, because it argues from final ends, that is, teleology, must one day reach the question: From where did these final causes arise? Since these final causes as precepts of eternal law are an ordinance of reason, they must come from somebody’s reason. As Aquinas argues, to be law they must be promulgated by someone. Ultimately, a natural law jurist must confront this question. Likewise, anyone’s ability to accurately know all of those principles of natural law and, more to the point, correctly apply them to particular circumstances, is severely limited without recourse to divine law. The history of unjust and evil laws and legal regimes throughout history is evidence of the difficult work of knowing and correctly applying the principles of the natural law. Succeeding in this task without recourse to divine revelation is analogous to building an edifice without consulting an architect. The approach of Finnis to minimize the role of God in natural law jurisprudence may have some initial success and overcome the initial mocking of critics like Nielsen, but I argue it will be ultimately unsatisfactory.

Moore offers a categorization of different metaphysical foundations for a natural law that can be very useful in explaining my answer to this question. Moore first formulates a two-pronged, general definition of any form of natural law theory: “(1) there are objective moral truths; and (2) the truth of any legal proposition necessarily depends, at least in part, on the truth of some corresponding moral proposition(s).”135 This definition clearly distinguishes natural law jurisprudence from positivism because it requires that laws (legal propositions) have a relationship to truths outside of the legal system. Yet, according to Moore, different proponents of this relational view can have very different understandings of the nonlegal truths. Moore identifies four possibilities:

  1. Moral realists who hold that the nonlegal propositions to which law must relate really exist independently of both (1) what people think them to be (mind-independent) and (2) human conventions (convention-independent) regardless of whether those truths both exist naturally and are known naturally (or through some suprasensible faculty).
  2. Naturalist moral realists who hold that the nonlegal propositions to which law must relate really exist, are mind- and convention independent, and exist in the natural world and can be known by a natural power or faculty.
  3. A particular species of naturalist who holds that “a universal and discrete human nature” determines the content of the nonlegal moral truths to which legal propositions must relate.
  4. Religious tradition-grounded naturalists who hold that the “(human) mind- and convention-independent” nonlegal truths to which legal propositions must relate “depend on the natural fact of divine command.”136

I will argue that one can fully comprehend the essence of law (speculative knowledge) and have greater success in reaching good (meaning true) judgments about what human laws ought to contain (practical knowledge) only from a perspective that combines both the third and fourth categories. A jurist who accepts both the real, naturally existing moral truths and their ontological origin in and revelation by the mind of God will attain greater speculative and practical knowledge of law than one who approaches jurisprudence from one of the other limited perspectives. Classical antiquity demonstrates that philosophers and jurists such as Aristotle, Plato, and Cicero accepted a natural law philosophy and jurisprudence and had significant success in acquiring speculative and practical knowledge of the law. Yet, their advocacy for natural law was inchoate because they could not clearly articulate the attributes of its divine origin. Their work, despite its greatness in some areas, clearly contains conclusions about the content of natural law that are, in light of Christian revelation, strikingly false. Aristotle’s claim that slavery is a natural and good state for some is only one example. Augustine, Gratian, and Aquinas surpassed the achievements of the ancients because they had recourse to the fuller source of knowledge in revelation.

A critical difference between natural law jurisprudence undertaken from one of the first three perspectives (listed above) alone and the combination of the third and fourth is the same difference that John L. Hill identifies between Greek philosophy and Christian philosophy. The former “tries to explain the world by giving us a pattern, whereas Christianity gives us a Person.”137 The revelation of the three divine persons within God makes philosophy, and hence law, personal rather than merely conceptual. Classical natural law jurisprudence makes law personal in contrast not only to the jurisprudence of Hart and Raz but also to that of Moore and Finnis.

Notwithstanding this and other differences, one can certainly be persuaded to accept and practice aspects of natural law jurisprudence without necessarily accepting the theological commitments of the fourth category, and fruitful conversation and dialectic can occur among scholars coming from all four perspectives. Yet, the fourth perspective offers the most complete and successful approach to solving the epistemological problems inherent in unaided natural law jurisprudence. Although intelligent conversation is possible and fruitful among those coming from all four categories, the benefits to be gained from accepting the commitments of the fourth category should not be ignored and left out of the discussion simply for the sake of gaining wider acceptance for natural law jurisprudence. Since all of those who argue from the first three categories lack the ultimate metaphysical foundation for law (and all of reality), they can only reach a certain extent of knowledge. Those who tend to try to appeal to positivists (or other non–natural law jurists) by arguing exclusively from the first three metaphysical positions do a disservice to, and ultimately undermine the deep metaphysical grounding of, natural law jurisprudence. Ignoring or downplaying the metaphysical foundations ultimately leads to their dismissal. As Jonathan Crowe has observed, the result is that, for Finnis, law does not really have an ontology; it is merely a hermeneutic to explain and justify normative social practices.138

A deeper consideration of eternal, natural, divine, and human law is necessary to fully understand what is lost by abandoning this fourth type of natural law jurisprudence. The metaphysical and theological claims of the natural law tradition are ultimately the most unique contribution it can bring to jurisprudence and should therefore not be left out of the discussion.

115.          Gratian, DecretumD.1 (my translation of humanum genus duobus regitur, naturali uidelicet iure et moribus.)

116.          Ibid., D.1, C.1; my translation of omnes leges aut diuinae sunt, aut humanae. Diuinae natura, humanae moribus constant, ideoque he discrepant, quoniam aliae aliis gentibus placent. §1. Fas lex diuina est: ius lex humana. Transire per agrum alienum, fas est, ius non est.

117.          Huguccio Pisanus, Summa Decretorum, in Monumenta Iuris Canonici Series A: Corpus Glossatorum, vol. 6, ed. Oldřich Přerovský (Biblioteca Apostolica Vaticana, 2006), 13 (glossing naturali uidelicet iure as id est diuino); see also Huguccio, Derivationes, quoted in Stephan Kuttner, The History of Ideas and Doctrines of

Canon Law in the Middle Ages (London: Variorum Reprints, 1980), V, 99. Drawing a similar parallel between positive justice and natural justice, which he calls fas, Huguccio claims that iustitia positiva has been made by man whereas naturalis justitia is extended from the effects of nature.

118.          Huguccio, Summa Decretorum, 14: Quo nomine comprehenditur quodlibet ius humanum, id est ab homine inuentum.

119.          Gratian, The Treatise on Laws (Decretum DD. 1– 20), vol. 2, trans. Augustine Thompson and James Gordley (Washington, DC: Catholic University of America Press, 1993), Ordinary Gloss to D.1.

120.          See Charlton T. Lewis et al., A Latin Dictionary: Founded on Andrews’ Edition of Freund’s Latin Dictionary (Oxford: Clarendon, 1879) (defining fasas “belonging to the religious language, the dictates of religion, divine law; opposed to jus, or human law”). The following are examples of the use of the word in the Bible: audiebant autem eum usque ad hoc verbum et levaverunt vocem suam dicentes tolle de terra eiusmodi non enim fas est eum vivere (Acts 22:22, Vulg.)—“And they heard him until this word, and then lifted up their voice, saying: Away with such an one from the earth; for it is not fit that he should live” (Acts 22:22, DV); contigit autem et septem fratres cum matre adprehensos conpelli a rege contra fas ad carnes porcinas flagris et taureis cruciatos” (2 Macc. 7:1, Vulg.)—“It came to pass also, that seven brethren, together with their mother, were apprehended, and compelled by the king to eat swine’s flesh against the law, for which end they were tormented with whips and scourges” (2 Macc. 7:1, DV); hii vero qui intus erant confidentes in stabilitate murorum et adparatu alimoniarum remissius agebant maledictis lacessentes Iudam ac blasphemantes et loquentes quae fas non est (2 Macc. 12:14, Vulg.)—“But they that were within it, trusting in the strength of the walls, and the provision of victuals, behaved in a more negligent manner, and provoked Judas with railing and blaspheming, and uttering such words as were not to be spoken” (2 Macc. 12:14, DV).

121.          Huguccio, Summa Decretorum, 20– 21.

122.          See Kenneth Pennington, “Lex Naturalis and Ius Naturale,” The Jurist 68 (2008): 571–7 3.

123.          See Lewis, A Latin Dictionary (jus: “that which is binding or obligatory; that which is binding by its nature, rightjusticeduty”).

124.          Justinian, Digest 1.1.11.

125.          Cicero, Letters to Atticus 1.16.6, /att1.shtml#6. Explaining how devastating it is to Rome when corrupt men render a wrong verdict, he says: triginta homines populi Romani levissimos ac nequissimos nummulis acceptis ius ac fas omne delere. The phrase sums up a complete obliteration of all rightness—ius ac fas.

126.          Justinian, Digest (my translation of iuris prudentia est divinarum atque humanarum rerum notitia, iusti atque iniusti scientia).

127.          Gratian, DecretumD.1, C.1.

128.          Cicero, “On the Laws,” in On the Commonwealth and On the Laws, ed.

James E.G. Zetzel (Cambridge: Cambridge University Press, 1999), 110.

129.          Ibid., 110– 11.

130.          Ibid., 111.

131.          Gratian, DecretumD.1.

132.          See Michael S. Moore, “Good without God,” in Natural Law, Liberalism, and Morality, ed. Robert P. George (Oxford: Clarendon, 2001), 221– 70.

133.          Kai Nielson, “The Myth of Natural Law,” in Law and Philosophy: A Symposium, ed. Sidney Hook (New York: New York University Press, 1964), 129. 134. Ibid., 130.

135.         Michael S. Moore, “Law as a Functional Kind,” in Natural Law Theory: Contemporary Essays, ed. Robert P. George (Oxford: Oxford University Press, 1992), 189– 90.

136.         Ibid., 190– 91.

137.         Hill, After the Natural Law, 55 (paraphrasing G.K. Chesterton). 138. Crowe, “Clarifying the Natural Law Thesis,” 168– 70.