Drawn from extracts in MDA Freeman (ed), Lloyd’s Introduction to Jurisprudence (Sweet & Maxwell, 8th ed, 2007) 137–143; Michael Head and Scott Mann, Law in Perspective (UNSW Press, 2012) 199–204.

Natural law theory is often contrasted with positivist theory, and is the older of the two. Freeman explains that ‘the essence of natural law may be said to lie in the constant assertion that there are objective moral principles which depend upon the nature of the universe and which can be discovered by reason.’ Head and Mann state that there are five aspects that can be used to define natural law: nature; ethical or moral considerations; religious precepts; social contract; and human reason. They provide examples of lines of reasoning embodied in those approaches:

  • the derivation of principles from observations of human behaviour,
  • the view that humans have a predetermined ‘end’ that can be ascertained by reflecting on humanity’s nature and needs,
  • the assertion that propositions of natural law are ‘self-evident’, whether given by God or an inherent and natural product of human society, and
  • the flexible belief that natural law has some variable content that changes depending upon the time, place and circumstances, thus accommodating different social orders.

The consequence of natural law theory is the implication that ‘bad’ laws can be inherently defective and perhaps not even be laws by that fact, and that the duty of obedience to official authority has limits. Bentham, in Anarchical Fallacies and A Fragment on Government, criticised Blackstone for suggesting in his Commentaries that the common law contains ‘natural rights’. Bentham wrote that ‘the natural tendency of such doctrine is to impel a man, by the force of conscience, to rise up against any law whatever that he happens not to like.’

Plato (427–347 BC) propounded a model of social order based on human reason, that largely obviated the need for a legal code. In Plato’s view, the law should not merely compel behaviour, but persuade and educate in virtue. In Apology, Plato maintains a view that the state cannot demand that its citizens commit evil, and that the only honourable option is to refuse such a demand. On the other hand, in Crito he states that individuals are obliged to follow laws that cause them wrong: while they must not harm others, they must submit themselves to the injustice of the state. Head and Mann list (and criticise) Plato’s three reasons for obedience:

The parent-child analogy —this is much over-stretched, not least because societies are historically forged and contain conflicting interests, pursued by adults, whereas children are largely dependent on their parents.

Social contract, that is, those who disagree can leave. The right to leave society is often unrealistic, as it is today for many refugees.

Unrest will destroy the social fabric. The social fabric may be the cause of intolerable injustice and hence discontent.

Aristotle, Plato’s student, argued in Nichomachean Ethics (350 BC) that political justice consists of a natural element and a legal element. The natural element is a universal law that exists extrinsically from what people think. The legal element involves the intricacies of justice: for example, the value of a prisoners ransom. Aristotle explains that this natural element is that which is true without human modification — that which is not law merely by virtue of convention and expediency, but which is fundamental everywhere. Aristotle adopted Plato’s view on the role of the state in encouraging what Aristotle believed was the inherent potential for good in humans. Further, Aristotle suggested the existence of universal justice, and his tutoring of Alexander the Great is linked the rise of stoicism (a belief in a rationally observable ‘cosmic reason’) as a school of philosophical thought.

Cicero, in De Re Publica (54–51 BC), reinforced Aristotle’s view that ‘true law’ is that which is in agreement with nature and of universal and infinite application, and adopted the universalism of stoicism. In Cicero’s view, it is sinful to attempt to alter or repeal or abolish this law, and impossible to do so regardless. But Cicero goes further than Aristotle (who was accepting of cultural and geographic variations in law), foreseeing a time when the divine, the creator of the natural law, would enforce it over all. Positive laws (that is, human-made laws) must be struck down if contrary to natural law. Cicero distinguishes three types of law: positive law (lex vulgus), celestial law (lex caelestis) and natural law (lex naturae). Positive law is essentially the exercise of political power, while celestial law, when accessed through rational insight and inquiry, would produce the natural law, a proper model for making laws.

Emperor Justinian’s Institutes (forming part of his Corpus Juris Civilis, a sixth-century codification of Roman Law) explains that the law nature has been taught by nature to all living creatures, including humans. Justinian writes that the law of nature is the origin of matrimony (Justinian specifically calls this a union of male and female), procreation and child raising that is exhibited across all species. Justinian maintains that all peoples adopt a hybrid of universal legal principles (natural law, jus gentium) with law that is peculiar to the community itself (civil law, jus civile). Like Cicero, Justinian maintains that the natural law comes from the divine and cannot be changed.

The transition to Christianity under Emperor Constantine in 312 AD necessitated the consolidation of ancient Graeco-Roman philosophy with Judaeo-Christian traditions. The consequence was a theory of natural law based on divine commands given in codified law (that is, the Biblical scriptures), an immutable set of principles and laws that justified both obedience and disobedience in whichever circumstances might arise. Head and Mann state that Christianity was used to legitimise the Roman Empire, as it would later legitimise the feudal order. They also acknowledge that having such a body of unchangeable laws is difficult to reconcile with change, citing Aquinas’ theory’s inability to deal with changing economic requirements.

Early Judaeo-Christian natural law theory was pioneered by St Augustine of Hippo (345–430), who asserted that ‘a just law is no law’ and, drawing from Cicero, compared unjust governments with criminal gangs that must use force to maintain authority (though Head and Mann quickly add that this did not necessarily give rise to a right of rebellion). In Augustine’s theory, laws that were had to be coercively enforced without being just carried no moral force. The positive law (lex temporalis) could only be just when derived from the eternal law (lex aeterna).

In contrast to Augustine’s minimalistic view of positive law as being restricted to coercive discouragement of sin, St Thomas Aquinas’ Summa Theologica (1265–1274) brought much of the pre-Christian philosophy to Catholic theology, and embraced Aristotle’s view that positive law was a ‘natural’ part of society. Aquinas states what could be considered the fundamental principle of law: that ‘Law is a rule or measure of action in virtue of which one is led to perform certain actions and restrained from the performance of others.’ Aquinas holds that the first principle of human action is reason, referring to Aristotle’s work. Aquinas argues that the human will must be regulated by reason if it is to have the authority of law.

According to Aquinas, the object of law is the common good: the law exists to maintain and further the well-being of the community, again referring to Aristotle who said that ‘We call that legal and just which makes for and preserves the well-being of the community through common political community.’ Aquinas acknowledges that the community, either directly or through a representative, orders affairs so as to secure the common good, and that private persons cannot compel ‘right living’, merely provide unenforceable advice. It is the duty of the community or its representative to compel obedience and inflict penalties. In a domestic setting, Aquinas holds that the head of a family may likewise make rules and regulations, ‘but not such as have, properly speaking, the force of law.’

Drawing on the above, Aquinas offers a definition of law as ‘a rational ordering of things which concern the common good; promulgated by whoever is charged with the care of the community.’

Like Cicero, Aquinas compartmentalises law into four categories: ‘eternal law’ (lex aeterna), ‘divine law’ (lex divine), ‘natural law’ (lex naturalis) and ‘human law’ (lex humana). Eternal law is the rational guidance of created things by the divine — the will of God. This is founded on the premise that if law is the commands of reason promulgated by the ruler of a community, then the universe is governed by the divine reason of God as ruler. The divine law, by contrast, is that which has been revealed to humans through scripture. The natural law is the participation of rational creatures in the eternal law: by virtue of their capacity to control their actions and the actions of others, they share an amount of divine reason. Human law is the consequence of needing particularity, and must be arrived at by reason and derived from the natural law to be ‘good.’

In this model, human law compels observance of the morally-sound natural law; laws that radically depart from the natural law are not laws and the moral obligation to obey fails. However, some amount of injustice must be tolerated to avoid potentially worse destabilisation at the hands of rebellions. Head and Mann state:

In the battle against the rising capitalist class, this doctrine became more openly reactionary. In the Counter-Reformation, later Thomists [(adherents of Aquinas’ theories)] insisted that to challenge positive law was to sin against the eternal law of God. Thus, before they were ousted by Cromwell, the Stuarts claimed ‘the Divine Right of Kings’.

According to Aquinas, the ‘order of the precepts of the natural law corresponds to the order of our natural inclinations’ which, he maintains, is towards good. The natural law preserves human life, and opposes its destruction. Humans also have other natural inclinations shared with animals: sexual relationships and the rearing of offspring among similar tendencies. Humans have ‘a natural inclination to know the truth about God and to live in society.’

An aspect of the natural law is that ‘it is proper for man to seek to act according to reason’, which moves from general principles to matters of details. Aquinas divides reason into the practical and speculative, which go about this transition in different ways. Speculative reason ‘is principally employed about necessary truths, which cannot be otherwise than they are’ and ‘practical reason is employed about contingent matters, into which human actions enter.’ As one drifts further from generality, the conclusions of reason become increasingly open to exception.

Aquinas holds that there is an absolute truth which, although not equally known to all, remains universally true (for example, the sum of the degrees of the angles in a triangle). This truth only exists in speculative reason; in practical reason the conclusions will not meet a universal standard of truth or rightness. While all persons recognise the rightness of acting according to reason (as in the necessity of repaying debts), practical reason may lead to the conclusion an otherwise rational act is irrational (such as where it would lead to injury). The more particular the case, the more exceptions are likely to occur.

From this, Aquinas concludes that broadly the natural law contains general principles that are universal which ought to guide human action. Exceptions are the result of the principle that reason ought to be applied when directing all human action that subverts principles which, if applied, would lead to an injurious or irrational outcome. Unlike Cicero, Aquinas holds that the precepts of natural law can change according to the circumstances: in specific cases, as explained.

In Aquinas’ view, the natural human state includes and inclination towards virtue can only be perfected by practicing a ‘certain discipline.’ This depends upon the assistance of the community to guide its members. Aquinas believes that some are more readily inclined towards virtue than others, and while advice and guidance can assist the former, the latter must be restrained by force and fear. ‘When they are thus prevented from doing evil, a quiet life is assured to the rest of the community; and they are themselves drawn eventually, by force of habit, to do voluntarily what once they did only out of fear, and so to practise virtue.’ This is the ‘discipline of law’ and is the very impetus for the enactment of laws. Without restraint, reason becomes a weapon to exploit base desires and cruelty.

Aquinas quotes St Augustine’s Del Libero Arbitrio: ‘There is no law unless it be just.’ The validity of law depends upon its justice, and in human affairs just laws are those which accord with the rule of reason, the first rule of natural law. ‘Thus all humanly enacted laws are in accord with reason to the extent that they derive from the natural law.’ According to Aquinas, conclusions arrived at through speculative reason are sanctioned by natural and human law, but those arrived at through practical reason are sanctioned only by human law.