Ius naturale: The Foundations of Modern Human Rights Discourse in the Natural Legalism of Thomas Aquinas Part I
Modern human rights discourse is the product of centuries of Western intellectual development. Though such discourse would not develop fully until the Early Modern period it is grounded in much earlier schools of thought and the Scholastic theologians of the Middle Ages made significant contributions to its development. Thomas Aquinas is one medieval thinker particularly important to the development of human rights discourse and it would be direct interpreters of his work who would give the concepts and discourse of human rights much of the shape which they take to this day. Of course, Aquinas did not write in terms strictly analogous to ‘human rights’ and it would be anachronistic to impose any such concept on his work but his natural law philosophy lays important foundations which would be applied by later Scholastic and humanistic thinkers to questions such as slavery, political authority, and war, which bore directly on the fields covered under the modern heading of ‘human rights’ and which made seminal contributions to the development of modern human rights discourse.
A necessary prolegomenon to any discussion of Thomistic moral-legal thought is the distinction between natural and positive law in Aquinas’ thought. Positive law, or, to employ Aquinas’ own terminology, human law, is, in Aquinas’ thinking, derived from natural law. This is not to say that civil legislation can be rationally deduced from a set of moral principles, a position frequently associated with Thomistic natural legalism, but that positive laws derive their moral legitimacy, and thus their moral authority over those theoretically bound to obey them, from accordance with the natural law. Aquinas states this point forcefully in the Summa Theologiae’s famed ‘Treatise on Law:’ “[e]very human law has just so much of the nature of law as it is derived from the law of nature. But if, in any point, it deflects from the law of nature it is no longer a law but a perversion of law.” Aquinas posits two means of deriving positive laws from the natural law. The first is the derivation of laws from premises which are themselves deduced from natural law. These are only the broadest principles, such as ‘harm no one’ or ‘do not commit murder’ and are not in themselves fully-fledged positive laws. The second is derivation by determination, in which specific civil legislation is built upon the bare bones of the natural law in a contingent manner. The manner is contingent because the specifics of the civil legislation could well be different and yet the law would still accord with the natural law. The natural law provides the rough shape which the law must take but human art must derive from this rough shape one of multiple possible specific forms. An example of this process of determination would be legislation requiring cars and other motor vehicles to drive on the right side of the road as a derivation from the natural law’s requirements of social order and state provision for the safety of citizens. The requirements of the natural law are no less fulfilled when the civil legislation requires driving on the left side of the road, since the specific form of the legislation is contingent. Law made by this process of determination is purely positive law and thus does not carry the weight of the natural law, though it is just so long as it is accordance with the natural law according to the principles of determination.
Aquinas is insistent that the natural law itself ought not be a motivator for human action. The purpose of the law is to make those subject to it good, that is, to foster their advancement in virtue. It does this providing a bar against which to judge actions, rather than motivations. One ought to act in accordance with the natural law not out of obedience to the law itself but because the natural law prescribes that which is itself good and which ought to be done. Positive laws may compel persons to obedience by threat of force but, Thomas insists, compliance by coercion is inferior to compliance by inclination, and the both natural and positive law have the task of training subjects in virtue in order they would become incline to obey the law, both positive and natural. The implications of the Thomistic distinctions between positive and natural law in terms of their substance, content, and intent are relevant for any discussion of human rights in Aquinas’s thought because they recommend the applicability of his ideas to the problems of human rights even when some of his specific theories of positive law present apparent barriers to that applicability.
Turning to the question of rights in Aquinas’ thought it is first necessary to examine Aquinas’ use of the different but closely related ideas of law and right. Ius and lex, the Latin words from Aquinas’ work translated into English as ‘right’ and ‘law’ respectively, are nuanced terms have been understood in different, sometimes distinct and at other times interchangeable ways over the millennia-long history of their use. Lex is the more stable of the two but ius can be interpreted as referring to a subjective right; ‘rightness’ in the abstract; or as being effectively synonymous with lex, even while retaining an underlying sense of rightness or fairness. The two meanings present in Aquinas are the classical understanding of objectively right relationships and the later meaning, deriving largely from the Church Fathers, of divine command or precept, in which latter sense it is roughly synonymous with lex. Aquinas was aware of and pointed out meanings of ius other than those which he himself applied, including the sense of subjective rights, but he deliberately avoids these other definitions. This has lead to varying modern and Early Modern interpretations of Aquinas’ use of ius, with the understanding that Aquinas understood ius in rigid terms of subjective right being prevalent since the interpretations of Salmanticensis Francisco de Vitoria and dominant among neo-Thomists but thoroughly, if excessively, rejected by 20th century jurist Michel Villey. However, it is incorrect to imagine that Aquinas understood a strict dichotomy between ius and lex or between the notions of ‘law’ and ‘right.’ Aquinas refers far more frequently to lex than to ius but he does not use them discretely, or, perhaps, consistently. The Treatise on Law and the Treatise on Justice and Prudence at times treat the concepts of the law of nature, natural law, natural right, and natural justice as interchangeable and at times distinguish between them in their more specialised meanings. Aquinas’ definition of justice, which he draws from Roman civil law, is to render to each what is his or her own, that is, to give to each what is properly theirs. Justice is thus the fulfilment of right, the right of persons or groups being the entire object of justice. Thomas goes so far as to say that right is identical to what is just. When discussing particular ‘rights,’ which ought to be understand not in the sense of subjective rights but in the Thomistic sense of mutual right and obligation in just relationships, it is important to note that Aquinas grounds the rights which he details not in humanity, as is often if decreasingly the case today, but in the inherent dignity that comes of being a person and thus of possessing a rational nature. A rational nature, for Aquinas, is the ground of human dignity, which is the ground of right.
There are two final nuances to the Thomistic understandings of justice and right which bear strongly upon human rights discourse. First, justice and right are fundamentally a matter of equality. Justice exists when persons have rendered to them what is rightfully theirs, such as paying wages due in exchange for labour. This fundamental equality is the foundational, first-order precept of the natural law itself. Secondly, Aquinas holds that natural right supersedes positive laws. Civil legislation which violates the natural rights of those theoretically subject to that legislation is overridden by the right(s) of those subjects. The fundamental human equality integral to the Thomistic concept of justice and the inviolable nature of natural rights contribute to the ultimate status which Aquinas assigns to all human persons as being free and equal. Justice, properly speaking, consists in equal measures of rights and duties, since the rights of one entail duties to that one in others and vice versa and this regard all subjects of rights and duties, that is, of justice, are equal. The strength of this Thomistic assertion can be readily overstated: John Finnis quotes Aquinas as saying, “[o]mnes hominess natura sunt pares;” ‘by nature all humans are equal.’ The strength of this quotation is more than a little lessened when one examines the context of the article from which it is taken, wherein Thomas restricts the just dominion of a master over a slave to bodily matters but asserts that in matters of the soul all human beings are equal and thus autonomous. The problematic of Aquinas’ position on slavery will be addressed below but for now it suffices to say that Aquinas’ conceptions of justice and right provide resources and foundations for the modern human rights principles of fundamental human equality and inalienable subjective rights, though Aquinas does not develop these resources as extensively as modern human rights discourse.
Part II of this series will examine more aspect of Aquinas’ thought relevant to modern human rights discourse as well as raising the large problematic of Thomistic natural slavery.
 Westberg, Daniel, “The Relation between Positive and Natural Law in Aquinas,” Journal of Law and Religion 11 (1994-1995), 3.
 ST I-II.95.2
 ST I-II.95.2
 Westberg, “Positive and Natural Law in Aquinas,” 4.
 Finnis, John, Aquinas: Moral, Political, and Legal Theory (New York: Oxford University Press, 1998), 268; ST I-II.95.2; ST II-II.57.2
 ST I-II.92.1, I-II.95.1
 Westberg, “Positive and Natural Law in Aquinas,” 10, 11.
 Westberg, “Positive and Natural Law in Aquinas,” 12; ST I-II.95.1
 Tierney, Brian, The Idea of Natural Rights: Studies on Natural Rights, Natural Law and Church Law 1150-1625 (Georgia: Scholars Press, 1997), 23, 26.
 Tierney, The Idea of Natural Rights, 22-23, 258; ST II-II.57.1
 Tierney, The Idea of Natural Rights, 23, 26, 257, 259; Cf. Villey, Michel, La formation de la pensée juridique moderne (Montchrétien, 1975), 50, 126.
 Klassen, David J., “Le droit naturel dans la pensée de Thomas d’Aquin,” in Louis-Léons Christians et al, eds., Droit naturel : relance l’histoire? (Brussels: Bruylant, 2008), 260.
 Klassen, “Le droit natural” 260; Tierney, The Idea of Natural Rights, 25.
 Finnis, Aquinas, 113; ST II-II.58.1
 ST II-II.57.1
 Finnis, Aquinas, 176.
 ST II-II.57.1
 Finnis, Aquinas, 136.
 Finnis, Aquinas, 136; ST II-II.57.2
 Finnis, Aquinas, 170.
 Finnis, Aquinas, 170 note 166.
 ST, II-II.104.5