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Published online by Cambridge University Press: 03 October 2024
What is the nature of law? The question that St. Thomas Aquinas answers in Summa Theologica I-II continues to be a crucial question in contemporary philosophy of law. Various scholars of jurisprudence attempt to identify the necessary features of law. Yet they struggle with the question, what kind of necessity is involved? Is it conceptual necessity? Metaphysical necessity? In this paper, I explore an alternative way of distinguishing different kinds of necessity that is found in Aquinas’ Commentary on Aristotle’s Physics. I argue that the three kinds of necessity simpliciter, from the formal, material, and efficient cause, and hypothetical necessity, from the final cause, are relevant for understanding how Aquinas’ definition of ‘law’—an ordinance of reason, for the common good, made by the one who has care for the community, and promulgated—is a necessary truth. This historically interesting approach offers insights for contemporary jurisprudence.
1. See St. Thomas Aquinas, Summa Theologica, translated by Fathers of the English Dominican Province (Benziger Brothers, 1947) 995 (Pt I-II, Q 90, a 4) [Aquinas, Summa].
2. Joseph Raz, Between Authority and Interpretation: On the Theory of Law and Practical Reason (Oxford University Press, 2009) at 24-25.
3. In the natural law tradition, see e.g. John Finnis, Natural Law and Natural Rights (Oxford University Press, 1980); Michael S Moore, “Law as a Functional Kind” in Robert P George, ed, Natural Law Theory: Contemporary Essays (Clarendon Press, 1992) 188; Jonathan Crowe, Natural Law and the Nature of Law (Cambridge University Press, 2019). For the legal positivist tradition, see HLA Hart, The Concept of Law, (Oxford University Press, 1972) at ch 1; Timothy Endicott, “The Generality of Law” in Luís Duarte d’Almeida, James Edwards & Andrea Dolcetti, eds, Reading HLA Hart’s ‘The Concept of Law’ (Hart, 2013) 15; Stefan Sciaraffa, “Constructed and Wild Conceptual Necessities in Contemporary Jurisprudence” (2015) 6:2 Jurisprudence 391. See also Yi Tong, “On the Nature of Necessary Truths in Jurisprudence: Putting Wittgensteinian Hinges to Use” (2021) 34:1 Can JL & Jur 203. I readily acknowledge that different theorists use different methodologies in their attempts to identify the necessary features of law, but a discussion of those important differences is largely outside the scope of this paper.
4. See Tong, supra note 3 at 207-08. Joseph Raz comes close to addressing this issue but does not; see Raz, supra note 2 at 26. In a subsequent chapter, he admits, “I will leave the question of the kind of necessity involved [in the nature of law] unexplored.” Raz, supra note 2 at 91.
5. Danny Priel, “Jurisprudence and Necessity” (2007) 20:1 Can JL & Jur 173 at 175 [emphasis in original, footnote removed].
6. Tong, supra note 3 at 205-06 [emphasis in original]. Joseph Raz responds to a similar objection: see Raz, supra note 2 at 24-36.
7. See Tong, supra note 3 at 231-34. His main example is “the change from the fundamental idea that law is the command of a sovereign, to be found in the writings of Thomas Hobbes (16th-17th century) and John Austin (18th-19th century), to the basic thought that law is a system of rules, norms, or principles, to be found in H.L.A. Hart, Hans Kelsen, and Ronald Dworkin’s writings in the contemporary world.” Tong, supra note 3 at 233 [emphasis in original].
8. Ibid at 232-33 [emphasis in original].
9. Michael S. Moore argues that ‘contingent necessity’ is no kind of necessity at all, and that it is based on an accidental generalization:
An accidental generalization is a generalization that is true of a finite sample size of things but that is not necessarily true because of the nature of the kind of things making up the sample. ‘All American lawyers are under seven feet tall’ is, as far as I know, true about the hundreds of thousands of American lawyers that exist. Yet the generalization is not necessarily true because it does not answer correctly the crucial counterfactual question, ‘If someone were over seven feet tall, would he not be a lawyer?’ There is, in short, no necessary connection between size and being a lawyer, only an accidental connection. Moore, supra note 3 at 199.
Tong could counter that what counts as a correct answer to a counterfactual question depends upon the particular culture’s conceptual scheme. Perhaps in the conceptual scheme used by Hobbes and Austin, for example, an affirmative answer is not allowed to the counterfactual question, ‘If something is not a command of a sovereign, could it still be a law?’
10. Aquinas, Summa, supra note 1 at 995 (Pt I-II, Q 90, a 4). Aquinas writes: “Et sic ex quatuor praedictis potest colligi definitio legis, quae nihil est aliud quam quaedam rationis ordinatio ad bonum commune, ab eo qui curam communitatis habet, promulgata.” RJ Henle, ed, Saint Thomas Aquinas: The Treatise on Law (Being Summa Theologiae, I-II, QQ. 90 Through 97), translated by RJ Henle (University of Notre Dame Press, 1993) at 145 (Pt I-II, Q 90, a 4, co §2) [Aquinas, Treatise].
11. See Aquinas, Summa, supra note 1 at 996-1025 (Pt I-II, QQ 91-97). R.J. Henle, S.J., explains: “The reader will note that St. Thomas’s definition, as applied to these four types of law is analogous, not univocal, inasmuch as each type fulfills some part(s) of the definition in a different but similar way.” RJ Henle, “Introductory Comment on Treatise Q 91” in Aquinas, Treatise, supra note 10, 148 at 149. John Finnis discusses the importance of focal meaning for a general theory of law in Finnis, supra note 3 at 9.
12. It is far outside the scope of this paper to discuss the many controversies surrounding logical, conceptual, physical, and metaphysical necessity.
13. Cf Tong, supra note 3 at 207. Tong lists three of the five kinds—logical, conceptual, and metaphysical necessity—but acknowledges there are others.
14. See e.g. Benson Mates, Elementary Logic, 2nd ed (Oxford University Press, 1972) at 14. Unfortunately, matters are not that simple. Anderson argues there is no fixed notion of logical necessity. See C Anthony Anderson, “Logical Necessity, Conceptual Necessity, and the Ontological Argument” in Mirosław Szatkowski, ed, God, Truth, and Other Enigmas (De Gruyter, 2015) at 3.
15. Ibid at 5 [emphasis in original].
16. One approach is brought forward by M. Marković, who illustrates the sort of effort (perhaps in vain) one must make to define ‘physical necessity’ without acknowledging essences. He begins with a general definition of ‘necessity’:
First of all we must bear in mind a concrete totality, i.e., a definite system of objects S which are relevant for our problem. The system has, on the one hand, some general characteristics that, in any given moment t open a field of possibilities F, i.e., enable us to project a set of possible states of the system in various other moments (of the future or the past). The system, on the other hand, contains also some particular limiting conditions LC, i.e., some rules or laws that restrict the actualization of abstract possibilities. To say then, that an x is necessary means that X is a nonempty subset of the set of possibilities F and that all other possibilities of the field F except x are excluded by the action of the limiting conditions LC. M Marković, “The Concept of Physical Necessity” in Patrick Suppes et al, eds, Logic, Methodology and Philosophy of Science IV: Proceedings of the Fourth International Congress for Logic, Methodology and Philosophy of Science, Bucharest, 1971 (North-Holland, 1973) 967 at 967-68.
He then defines ‘physical necessity’: “To say, therefore, that a certain type of event x is physically necessary means: (a) that x is a subset of a field of apriori possibilities of the given field of physical objects; (b) that established physical laws are incompatible with any other possibility of the given field except x.” Ibid at 973 [emphasis in original].
17. Kit Fine, “Essence and Modality: The Second Philosophical Perspectives Lecture” (1994) 8 Philosophical Perspectives 1 at 9-10 [footnote removed]. See also Fabrice Correia, “On the Reduction of Necessity to Essence” (2012) 84:3 Philosophy & Phenomenological Research 639.
18. David Kelley offers the following conventional definition of ‘necessary condition’: “A given causal factor a is a necessary condition for an effect E when E cannot exist or occur without a.” David Kelley, The Art of Reasoning: An Introduction to Logic, 4th ed (Norton, 2014) at 424 [emphasis in original]. Cf Aristotle, “Metaphysics” in Jonathon Barnes, ed, The Complete Works of Aristotle: The Revised Oxford Translation (Princeton University Press, 1984) 1552 at 1603 (V.5.1015a20-25) [Aristotle, “Metaphysics”].
19. In contrast, Stefan Sciaraffa argues conceptual necessity is applicable to the “demarcation project” of determining the necessary features of law. Sciaraffa, supra note 3 at 392.
20. Aquinas, Summa, supra note 1 at 993 (Pt I-II, Q 90, a 1, citing Lib. i, ff., De Const. Prin. leg. I). “[Q]uod placuit principi, legis habet vigorem.” Aquinas, Treatise, supra note 10 at 122 (Pt I-II, Q 90, a 1).
21. Ibid at 994 (Pt I-II, Q 90, a 1, ad 3).
22. Moore argues that metaphysical necessity does apply to the nature of law. “A natural lawyer should say that the essence of law is such that it includes justice, among other things. Necessarily, that is, if some system, norm, or decision is unjust, it is not legal. Not as a matter of conventional usage of the word ‘law’ (analytical necessity); not as a matter of universal social practices (contingent necessity); but as a matter of the nature of one of the things that exists in the world, namely, law.” Moore, supra note 3 at 200 [emphasis in original]. Sciaraffa counters that “the idea of metaphysical necessity is vexed and contentious as applied to any object, yet no legal theorist has staked out a plausible account of such necessities in general or as applied to law specifically.” Sciaraffa, supra note 3 at 392. He adds that it “does not saddle legal theorists with implausibly sublime claims about the metaphysically necessary features of law” ( ibid at 393).
23. Aristotle, “Physics” in Barnes, supra note 18, 315 at 341 (II.9.199b33-200b11). Also see Aristotle’s definition of ‘necessary’ in “Metaphysics”: “We say that that which cannot be otherwise is necessarily so. And from this sense of ‘necessary’ all the others are somehow derived.” Aristotle, “Metaphysics”, supra note 18 at 1603 (V.5.1015a34-35).
24. St. Thomas Aquinas, Commentary on Aristotle’s Physics, translated by Richard J Blackwell, Richard J Spath & W Edmund Thirlkel (Routledge & Kegan Paul, 1963) at 124 (II, L 15, §270) [Aquinas, Commentary].
25. Ibid.
26. To note a further connection, Aristotle’s account of ‘compulsion’ seems to be a subset of physical necessity: see Aristotle, “Metaphysics”, supra note 18 at 1603 (V.5.1015a26-33).
27. Aquinas, Commentary, supra note 24 at 124 (II, L 15, §270).
28. Ibid .
29. Aquinas would add that, for material substances such as humans and water, metaphysical necessity must also include the necessity from the material cause. See ibid at 82-86 (II, L 4, §§167-75).
30. For a contemporary natural law theorist who recognizes the importance of hypothetical necessity, see Mark C Murphy, “The Explanatory Role of the Weak Natural Law Thesis” in Wil Waluchow & Stefan Sciaraffa, Philosophical Foundations of the Nature of Law, (Oxford University Press, 2013) 2.
31. See Aristotle, “Physics”, supra note 23 at 341 (II.9.200a15-18); Aquinas, Commentary, supra note 24 at 126-27 (II, L 15, §273). For discussions on the differences between the natural philosopher and the mathematician—in particular, the way the former investigates forms in sensible matter whereas the latter abstracts from sensible matter—see Aristotle, “Physics”, supra note 23 at 330-31 (II.2.193b32-194a5); Aquinas, Commentary, supra note 24 at 78-79 (II, L 3, §§ 159-61).
32. See Aristotle, “Physics”, supra note 23 at 340 (II.8.199a9-32). See also ibid at 341 (II.9.199b34-200b11); Aristotle, “On Generation and Corruption” in Barnes, supra note 18, 512 at 549 (II.9.335b5-8); Aristotle, “Parts of Animals” in Barnes, supra note 18, 994 at 994, 996 (I.1.639b14-640a10, I.1.640a33-b4).
33. Aristotle, “Physics”, supra note 23 at 340 (II.8.199a30-33). See also Aquinas, Commentary, supra note 24 at 120 (II, L13, §260).
34. Cf Aristotle, “On the Soul” in Barnes, supra note 18, 656 at 656 (II.1.412a20-21).
35. This point is scattered, usually implicitly, throughout Aristotle’s corpus. See e.g. Aristotle, “History of Animals” in Barnes, supra note 18, 774 at 848, 921, 949 (IV.9.536b2; VIII.1.588a15-b3; IX.1.608b7-13); Aristotle, “Parts of Animals”, supra note 32 at 995-96, 1030, 1032 (I.1.640a19-b4; III.1.661b15; 662b19-21); Aristotle, “Nicomachean Ethics” in Barnes, supra note 18, 1729 at 1735 (I.7.1097b24-1098a17); Aristotle, “Politics” in Barnes, supra note 18, 1986 at 1987-88 (I.2.1253a5-18).
36. See Aristotle, “Physics”, supra note 23 at 338 (II.7.198a23-24).
37. Aquinas, Commentary, supra note 24 at 114 (II, L11, §247). Aristotle discusses malformed humans in Aristotle, “Generation of Animals” in Barnes, supra note 18, 1111 at 1190-91 (IV.3.769b5-30). For a brief discussion of Aquinas’ account of monsters, see Steven J Jensen, “Of Gnome and Gnomes: The Virtue of Higher Discernment and the Production of Monsters” (2008) 82:3 American Catholic Philosophical Q 411.
38. See Aristotle, “Physics”, supra note 23 at 340 (II.8.199b1-7).
39. CDC Reeve, Action, Contemplation, and Happiness (Harvard University Press, 2012) at 81, translating Aristotle, “Generation of Animals” in Immanuel Bekker, ed, Aristotelis Opera (de Gruyter, 1970) (IV.10.778a4-9).
40. Aquinas, Commentary, supra note 24 at 115 (II, L11, §248) [footnote omitted].
41. That is, nature doesn’t act for the sake of an end that is superior simpliciter; rather it acts for the sake of an end that is superior relative to the kind of thing in question. For instance, dogs have pronounced canine teeth whereas cattle do not because dogs are carnivores and cattle are not.
42. Aquinas, Commentary, supra note 24 at 115 (II, L11, §249).
43. Ibid at 127 (II, L15, §274).
44. Ibid at 128 (II, L15, §274).
45. There are more recent examples of using simple artifacts to provide insights into the nature of law: i.e., for a discussion of knives, see Joseph Raz, The Authority of Law: Essays on Law and Morality (Clarendon Press, 1979) at 225-26; for a discussion of chairs, see Endicott, supra note 3 at 31-33.
46. Aquinas’ definition is duller than mine: “For if one wishes to define the operation of a saw (which is a division of a certain sort which will not occur unless the saw has teeth, and these teeth are not suitable for cutting unless they are of iron), it will be necessary to place iron in the definition of saw.” Aquinas, Commentary, supra note 24 at 128 (II, L15, §274).
47. “Ordĭnātĭo: ōnis,’ f. [ordino]: a setting in order, regulating, arranging; an order, arrangement, regulation (mostly post Aug.).” EA Andrews, Charlton T Lewis & Charles Short, eds, Harper’s Latin Dictionary: A New Latin Dictionary Founded on the Translation of Freund’s Latin-German Lexicon (Harper Bros, 1841) at 1277, sub verbo “ordinatio”.
48. Cf RJ Henle, “General Doctrinal Background for the Treatise” in Aquinas, Treatise, supra note 10, 38 at 45 [Henle, “Doctrinal Background”]. This part of the definition must be interpreted analogically when the lawgiver is God, in part because His knowledge is not discursive: see e.g. Aquinas, Summa, supra note 1 at 77, 1004 (Pt I, Q 14, a 7; Pt I-II, Q 93, a, 1, ad 3).
50. See Aquinas, Summa, supra note 1 at 993 (Pt I-II, Q 90, a 1, ad 2). Aquinas alludes to Aristotle, “Nicomachean Ethics”, supra note 35 at 1811 (VII.3.1146b35-1147a9). See also Aristotle, “Movement of Animals” in Barnes, supra note 18, 1087 at 1091-92 (7.701a6-701b1).
51. Aquinas’ reply to the third objection in Summa, which I cited earlier, shows that he takes it to be necessary that law is based on reason. See Aquinas, Summa, supra note 1 at 993 (Pt I-II, Q 90, a 1, ad 3).
52. The common good in question changes when applied to eternal law, divine law, and natural law. For instance, concerning eternal law Henle writes: “God’s relationship to created things is not only in the order of formal causality [as exemplars]. There is need also of a final cause and this is the ordination of all things to the final cause (the end) of all created things. This is the ordination of all things to the Common Good of creation which is the happiness of all mankind.” RJ Henle, “Comment on Treatise Q 93, a1, ad 1” in Aquinas, Treatise, supra note 10, 200 at 201.
53. Deferrari et al explain ‘beatitudo’ and ‘felicitas’ are synonyms: see Roy J Deferrai, M Inviolata Barry& Ignatius McGuiness, A Lexicon of St. Thomas Aquinas based on The Summa Theologica and selected passages of his other works (Catholic University of America Press, 1948) at 106, sub verbo “beatitudo”. Since current understandings of ‘happiness’ are infected with subjectivism, I translate the terms as ‘genuine human happiness’ to try to capture their objectivity as the ultimate end.
54. Aquinas, Summa, supra note 1 at 994 (Pt I-II, Q 90, a 2).
55. Ibid. Henle comments, “St. Thomas’s answer that law is always ordered to the Common Good sharply distinguishes his philosophy of law from that of Positivists, Utilitarians, Realists and similar philosophies.… Laws which serve the interests of rulers or of privileged groups, may indeed be called laws secundum quid, but they are not laws in the full sense or simpliciter since they fail in an essential point.” RJ Henle, “Introductory Comment on Treatise Q 90, a2” in Aquinas, Treatise, supra note 10 at 127. Using the terminology of Timothy Endicott, Aquinas is employing a paradigm-based account of law; see Endicott, supra note 3 at 28-33.
56. Cf Aquinas, Summa, supra note 1 at 1013-18 (Pt I-II, Q 95, a 1 - Q 96, a 1).
57. In the case of eternal law, all actions and movements are subject to it and directed by it; see ibid at 1003(Pt I-II, Q 93, a 1).
58. Cf Aquinas, Commentary, supra note 24 at 114 (II, L11, §248).
59. Cf Aquinas, Summa, supra note 1 at 110, 1013, 1018 (Pt I-II, Q 94, a 4; Pt I-II, Q 95, a 1; Pt I-II, Q 96, a 2).
60. This limitation does not apply to eternal law; see ibid at 1006 (Pt I-II, Q 93, a 5, ad 3).
61. I thank an anonymous referee for raising this objection.
62. Cf Aquinas, Summa, supra note 1 at 664 (Pt I-II, Q 18, a 2, ad 2).
63. Ibid at 1016 (Pt I-II, Q 95, a 4).
64. Henle explains, “Promulgation is reducible to two categories of causes. Viewed as active promulgating, it is part of the activity of the lawgiver and so belongs to the efficient cause. Viewed as the result of the activity of the efficient cause, it is reducible to the formal cause, the state of being promulgated.” Henle, “Doctrinal Background”, supra note 48 at 87.
65. In eternal law, divine law, and natural law, the proper authority is God; see Aquinas, Summa, supra note 1 at 996,998 (Pt I-II, Q 91, a 1, a 2, a 4).
66. Aquinas acknowledges that custom can obtain the force of law, and so serve as the efficient cause of human laws: see ibid at 1023(Pt I-II, Q 97, a 3). Cf Sciaraffa, supra note 3 at 406.
67. Of course, I acknowledge proper human authorities may be mistaken about what promotes the common good or, because of personal corruption, issue laws that are not based on reason. Such laws are laws secundum quid, not laws simpliciter.
68. Cf Aquinas, Summa, supra note 1 at 1010, 1021, 1694 (Pt I-II, Q 94, a 4; Q 96 a 6; Pt II, Q 120, a 1).
69. Ibid at 995 (Pt I-II, Q 90, a 4). As Joseph Raz notes, “The law must be open and adequately publicized. If it is to guide people they must be able to find out what it is. For the same reason its meaning must be clear. An ambiguous, vague, obscure, or imprecise law is likely to mislead or confuse at least some of those who desire to be guided by it.” Raz, supra note 45 at 214.
70. See e.g. Aquinas, Summa, supra note 1 at 1010-25 (Pt I-II, Q 94 aa 4-6; QQ 95-97). While my focus is on human law, let me note that Aquinas would agree with Jonathan Crowe that even the natural law can change over time although perhaps not for all the reasons Crowe gives: see ibid at 1011 (PT I-II, Q 94, a 5); Crowe, supra note 3.
71. The Oxford English Dictionary: Volume II C, (Oxford University Press, 1961) at 524 sub verbo “clothes”.
72. See Aquinas, Summa, supra note 1 at 1022 (PT I-II, Q 97, a 1).
73. Danny Priel raises a counterexample to the claim that human law necessarily orders human actions:
In most countries in Europe there used to be a practice of trying animals that caused harm. In these cases pigs, dogs, horses, rats, worms, beetles, and many other animals that caused harm to humans or property had been prosecuted and often condemned to death for their “crimes”. These trials were conducted with what seems from remaining court records like the same mix of solemnity and ritual found in criminal trials of humans. There was a judge, a prosecutor, an appointed counsel for the defence; witnesses were questioned; and if convicted the animals were subjected to “human” punishment like hanging. The trials were not concerned only with questions of identity, but also with issues of culpability, and in some cases the animals were even acquitted for lack of the requisite mens rea.… So we have here what look like legal norms addressed at certain individuals. These individuals were not the owners of the animals but the animals themselves.… But how are we to treat these laws? The animals in these cases could not be guided by the law, and therefore these laws did not have the capacity to guide those they were directed at. So are we to conclude … that guidance is not a necessary feature of law? Or perhaps that these are laws only because they belong to a legal system that includes other norms that are capable of guiding action of human beings? I am not sure how these questions should be answered. Priel, supra note 5 at 183-84 [footnotes omitted].
I think Aquinas would answer that human actions are the material cause of human laws simpliciter. Human laws applied to brute animals are laws secundum quid.
74. Aquinas, Summa, supra note 1 at 1009 (Pt I-II, Q 94, a 2).
75. RJ Henle, “Comment on Treatise Q 94, a2, co §3” in Aquinas, Treatise, supra note 10, 247 at 248.
76. Henle, “Doctrinal Background”, supra note 48 at 87.
77. See e.g. ibid at 87, 263.
78. Aquinas, Summa, supra note 1 at 1470 (Pt II, Q 64, a 6).
79. Ibid at 1479 (Pt II, Q 66, a 5).
80. Aquinas, Treatise, supra note 10 at 269 (Q 94, a 5).
81. See Aquinas, Summa, supra note 1 at 1014 (Pt I-II, Q 95, a 2). Finnis discusses the derivation of human (positive) law from natural law in Finnis, supra note 3 at 281-90.
82. Finnis offers a very helpful example:
If material goods are to be used efficiently for human well-being … there must normally be a regime of private property.… This regime will be constituted by rules assigning property rights in such goods, or many of them, to individuals or small groups. But precisely what rules should be laid down in order to constitute such a regime is not settled (‘determined’) by this general requirement of justice. Reasonable choice of such rules is to some extent guided by the circumstances of a particular society, and to some extent ‘arbitrary’. The rules adopted will thus for the most part be determinationes of the general requirement—derived from it but not entailed by it even in conjunction with a description of those particular circumstances. Ibid at 285-86.
83. See Aquinas, Summa, supra note 1 at 1022 (Pt I-II, Q 97, a1).
84. See ibid at 1012 (Pt II, Q 94, a 6).