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Natural law, Aquinas and the Magisterium

Published online by Cambridge University Press:  01 January 2024


The Catholic Church claims that its ethical teaching, especially on sex, is based upon natural law. I first show that natural law theories prior to the Middle Ages provide no authority for the Church's teaching on sex. I then examine Aquinas's teaching on natural functions and natural law in the two Summae. I suggest that he partly anticipates Enlightenment thinking about law and morals. I compare his theory of natural law with that of Germain Grisez and John Finnis. Finally, I examine the notion of a principle of practical reasoning and indicate how such principles could be formulated to correspond to elements in human nature.

Original Article
Copyright © 2014 The Dominican Council

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1 Catechism of the Catholic Church (London, Geoffrey Chapman, 1999), s. 2357Google Scholar.

2 Catechism 2352.

3 Humanae Vitae 490–1, quoted in Veritatis Splendor 80.

4 Catechism 2353.

5 Catechism 1755.

6 Catechism 2390.

7 Compendium of the Catechism of the Catholic Church (London, Catholic Truth Society, 2006), s. 430Google Scholar.

8 Natural Law (London, Hutchinson, 1951), pp. 78, 119–20Google Scholar.

9 Natural Law and Natural Rights (Oxford, Oxford University Press, 2nd edition. 2011), pp. 18, 251.

10 Diels, /Kranz, , Fragments of the Presocratics (Dublin/Zurich: Weidmann, 1966), 87 B 44Google Scholar. The fragment is mistranslated in Freeman's, Kathleen Ancilla to the Pre-Socratic Philosophers (Oxford: Basil Blackwell, 1962)Google Scholar, which makes him speak of ‘laws’ implanted by nature.

11 Quoted by d’Entrèves, Natural Law p. 8.

12 Diels/Kranz, 22 B 114.

13 See Diogenes Laertius 2.22 and Barnes, Jonathan, The Presocratic Philosophers (London: Routledge, 1982), pp. 57–8Google Scholar.

14 Fragments of the Old Stoics, ed. Arnim, H. von, (Leipzig: 1903–5), 3. 68Google Scholar; Long, A.A. and Sedley, D.N., The Hellenistic Philosophers (Cambridge: Cambridge University Press, 1990), 60 AGoogle Scholar

15 Zeno, in Diogenes Laertius 7. 87.

16 Stobaeus 2.75.11–2.76.8; Long and Sedley 63 B.

17 Diogenes Laertius 7. 85–6. See also von Arnim 2. 1002.)

18 Diogenes Laertius 7. 33.

19 Plutarch, Stoic Self-refutations, 1044 F – 1045 A; Long and Sedley 67 F.

20 Two Concepts of Liberty (Oxford: Clarendon Press, 1958), pp. 1925Google Scholar.

21 See, for instance, 2.1–2; 4. 1.

22 Tusculan Disputations 5.40–1.

23 Cicero, De Finibus 3. 62–8.

24 Von Arnim 3.325, Long and Sedley 67 R; echoed in Cicero's De Republica 3. 325 (Long and Sedley 67 S)

25 Natural Law, Ch. 1.

26 De Republica 3. 33. Cicero is here speaking in the person of a Stoic, for his understanding of the god of Stoicism see his De Natura Deorum 1. 39.

27 Distinction 1, quoted by Aquinas ST 1a 2ae q. 94 a. 4.

28 Natural Law, p. 38.

29 London: Incorporated Catholic Truth Society, 2012.

30 The parts he mentions, the concupiscibilis and the irascibilis, are Plato's epithumêtikon and thumoeides.

31 De Legibus, 1619.

32 De Iure Belli ac Pacis, 1625.

33 De Iure Naturae et Gentium, 1672.

34 Pufendorf, De Iure Naturae 2. 3. 2.

35 Grotius, De Iure Belli 1.1.10; Pufendorf, De Iure Naturae 1. 2, and see Barbeyrac's Historical and Critical Account of the Science of Morality, Ch. 2.

36 On divine commands, Plato, Euthyphro 10–11; on human laws, D'Entreves p. 115, ius quia iustum.

37 Essay 2. 28. 5; my emphasis.

38 Essay 2. 28. 8.

39 De Iure Naturae 1. 2. 6–7.

40 Leviathan 1. 6.

41 Natural Law, p. 45.

42 Leviathan 1. 14.

43 De Legibus 1. 2. 5.

44 De Iure Belli 1. 1. 3-6

45 De Iure Naturae 2. 2. 3.

46 See Murray, Alexander, Reason and Society in the Middle Ages (Oxford: Clarendon Press 1978)Google Scholar.

47 Thelêma, Matthew 6.11

48 Grisez, Germain, Contraception and the Natural Law, (Milwaukee: Bruce, 1964)Google Scholar.

49 John Finnis, Natural Law, pp. vii, 53, 55, 76

50 Unlike Xenophon's Socrates (Memorabilia 3. 8. 3) but like Moore, G.E. in Principia Ethica (Cambridge University Press 1908), s. 50Google Scholar.

51 Grisez, p. 50; the principles of practical reason are ‘fundamental prescriptions’, p. 61; ‘we are careful not to commit the usual error of inferring from a preferred set of facts to an illicit conclusion that these facts imply obligation’, p. 65. Similarly Finnis, pp. 37, 47.

52 Treatise of Hume Nature, ed. Selby-Bigge, L.A. (Oxford: Clarendon Press 1888), p. 458Google Scholar.

53 ‘The first principle of practical reason’ in Aquinas, ed. Kenny, Anthony (London: Macmillan, 1970), p. 375Google Scholar.

54 See, for instance. Lemmon, E.J., Beginning Logic (London : Nelson, 1965), pp. 912Google Scholar.

55 This tendency is documented by Mary Midgley in Are You an Illusion? (Durham: Acumen 2014)Google Scholar.

56 I think they correspond in part to Plato's parts of the psyche: see my ‘Trisecting the Psyche’, Philosophical Writings (1996) pp. 92–106; and also Anthony Kenny, ‘Mental Health in Plato's Republic’, Proceedings of the British Academy 1969, Price, Anthony, ‘Plato and Freud’, in Gill, Christopher, ed., The Person and the Human Mind (Oxford: Clarendon Press, 1990)CrossRefGoogle Scholar and Burnyeat, Myles, ‘’The Truth of Tripartition’, in Proceedings of the Aristotelian Society 106 (2006), pp. 122CrossRefGoogle Scholar.