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"It is through conscience that human beings see and recognize the demands of the divine law. They are bound to follow their conscience faithfully in everything they do."
Religious Liberty, no 2.

Natural Law

from Oxford Companion to Christian Thought.
published by Oxford University Press 2000

by Adrian Hastings


Adrian HastingsThe concept of natural law may be Aristotle’s principal legacy to Christian thought but it was Aquinas who set out its character in theological terms and his teaching has domin­ated natural law thinking ever since. Nothing may provide the fault line between classical Catholic and Protestant approaches to ethical theory better than the former’s insistence upon natural law and its rejection or belittlement by the latter.

Aquinas defines natural law as a participation in the eternal law by rational creatures (ST I-II q. 91 a. 2). It signifies the very functioning of a person’s practical reason with its inbuilt commitment to seek­ing good and avoiding evil. In this the intellect is enlightened by the divine law which it can reject but not escape. From this first inbuilt quest of the good follow other primary principles of natural law relating to truth, justice, and the like. We do not discover the existence of natural law as an inference from the study of our bodily functions and needs, although such study undoubtedly helps iden­tify secondary principles and conclusions. The root idea of natural law is that we, being rational, are also inherently moral beings, and that the exercise of moral judgement reflects what God has made us, and necessarily opens to us an awareness of divine law, whether or not we recognize it as such. In its primary principles, natural law is absolutely immutable, but not so in its secondary principles. That is to say, people can reason­ably conclude in regard to some particulars that what is good or bad in one cultural condition is otherwise in another. Aquinas explicitly agrees that natural law can change in certain particulars (ST HI q. 95 a. 5). Thus polygamy could be against natural law in one society but acceptable to it elsewhere. In conditions of high infant mortality such as long prevailed almost everywhere, contraception could be morally unacceptable, but, in conditions of low infant mortality and high population increase, the opposite might be the case. While one of the best-known of encyclicals, Paul VTs Humanae Vitae (1968), denies that contraception is ever acceptable accord­ing to natural law, many upholders of natural law would disagree.

The importance of this concept is that it universalises morality, providing a common basis for people of all faiths and none, without wholly standardizing it. It thus grounds the concept of conscience, establishing a moral link between humanity and God, present even when the link itself is unrecognized; it upholds a unified moral context for the entire human creation and justifies the claim that grace perfects nature rather than destroying or ignoring it, while presupposing that the moral judgement is not wholly disrupted by original sin. It also provides a template for the polit­ical order, including a concept of the ‘common good’, implicit in the construction of positive law, and an ultimate justification for revolution when this is gravely ignored by a tyrannical ruler

The Thomist concept of natural law was enlarged and applied to establishing a basis for international relations by Francisco de Vi­toria, a Dominican theologian in 16th-century Salamanca, often called the 'father of international law'. Bartolome de Las Casas, another Dominican, the defender of the native American peoples against Spanish oppression, made use of Vitoria’s teaching notably in the famous debate held between him and Gines Sepulveda by royal command at Valladolid in 1551. While Sepulveda appealed to Aristotle's doctrine of‘slaves by nature' to justify the enslavement of Americans, Las Casas, following Vitoria, insisted on the natural rights of everyone. Christian 'natural law’ had thus moved far be­yond Aristotelian ‘natural law’. In the 17th century the Dutch jurist and theologian, Hugo Grotius, wrote his Law of War and Peace (1625), which further elaborated this system of ideas so that he has been accorded the same title as Vitoria. After Grotius natural law thinking was increasingly secularised and rewritten as a theory of ‘natural rights’, understood apart from God. The Universal Declaration of Human Rights (1948) was derived from this tradition, while John XXIII’s encyclical Pacem in Terris (1963) well represents its continued Catholic use for interpreting the political order.

The more these ideas were secularised and politicised, the less they appeared to belong to theology. For Luther and much Protestant thought their presuppositions were anyway unacceptable. Original sin had so corrupted human nature that, without the help of revelation and grace, human reason could not participate in divine law. In the 20th century Barth forcefully reasserted this view, rejecting natural law together with natural theology and natural religion as falsely pretending to bridge from the creature’s side the chasm between humanity and God. Many Protestants, however, have always retained a commitment to natural law from Grotius and Hooker, who used it in his argument against the Puritan appeal to the bible alone, through to Reinhold Niebuhr and William Temple’s Christianity and Social Order (1942).

There was a marked revival of natural law thinking among both theologians and jurists in the later 20th century, and with it a revival of the dispute as to whether it can be coherently conceived apart from God. Quite clearly not for Aquinas, but for many modem jurists it can. Some arguments against natural law, though frequently repeated, have little validity. It is said to include an unacceptable inference from ‘is’ to ‘ought’, but this is not the case. It does not infer ‘ought’ from anything but recognizes it as an inescapable element in the practical reason, a pre-inferential part of ‘is’. Again, it is said to be unworkable because it implies an ahistorical immobility in morality, but, as we have seen, this is simply a misunderstanding. Finally, it is said to provide an inadequate programme for a Christian ethic. That is true but irrelevant. Christian morality does not deny natural morality but it has to go far beyond it.

d’Entreves, A. P., Natural Law (1951).

Finnis, John, Natural Law and Natural Rights (1980)

Niebuhr, Reinhold, The Nature and Destiny of Man (1964).

Westerman,Pauline, The Disintegration of Natural Law (1998).