This essay will explore two of the most fundamental and competing theories in legal philosophy: natural law and legal positivism. The central question that divides these schools of thought is whether there is a necessary connection between law and morality. Natural law theorists argue that for a law to be valid, it must align with a higher moral code. In contrast, legal positivists maintain that the validity of a law depends on its source and how it was made, not on its moral content. This essay will explain the core principles of each theory, using key thinkers to illustrate their ideas. It will then compare their approaches, particularly in the context of unjust laws, before considering their relevance within the English legal system. It will be argued that while legal positivism offers a more accurate description of how laws are identified and applied in a modern state, natural law provides an essential moral benchmark for evaluating the justice of those laws.
The Theory of Natural Law
Natural law is one of the oldest concepts in legal jurisprudence, with its origins tracing back to ancient Greece. At its heart is the belief that there are universal moral principles that are inherent in nature and discoverable through human reason. These principles form a "higher law" against which man-made, or positive, law can be judged. The famous maxim often associated with natural law, first articulated by St Augustine, is lex injusta non est lex – an unjust law is not a law at all. This means that a rule that is profoundly immoral cannot be considered a valid law and carries no obligation to be obeyed.
Classical thinkers like Aristotle suggested that the purpose of law was to help citizens achieve a ‘good life’ by adhering to principles of natural justice. This idea was developed further in the medieval period by St Thomas Aquinas, who provided a comprehensive Christian framework for natural law. Aquinas (cited in Martin, 2017) distinguished between four types of law: Eternal Law (God’s plan for the universe), Divine Law (revealed in scripture), Natural Law (the part of Eternal Law discoverable by human reason), and Human Law. For Aquinas, Human Law, which is equivalent to positive law, is only valid insofar as it is derived from and does not contradict Natural Law. A government that enacts laws against the natural law (for example, laws that violate the principle of preserving human life) loses its moral authority to rule.
In the 20th century, following the atrocities of the Second World War, natural law theory experienced a revival. Lon Fuller, in his work The Morality of Law, offered a secular, procedural version of natural law. Fuller (1969) argued that law has an ‘inner morality’. For a system of rules to be properly called a legal system, it must satisfy eight key principles. These include that laws must be publicised, clear, non-contradictory, and consistently applied. For Fuller, a system like that of Nazi Germany, which used secret and retrospective laws, failed to meet these procedural requirements and therefore could not be considered a true legal system. He argued that this failure in procedural morality meant the system was not just bad law, but not law at all.
The Theory of Legal Positivism
Legal positivism emerged in the 19th century as a reaction against the dominance of natural law theory. Its central argument is the "separation thesis": the idea that there is no necessary logical connection between law and morality. For a positivist, the question of "what the law is" is separate from the question of "what the law ought to be". A law can be a valid law even if it is morally wrong. Its validity comes from its source, not its content.
One of the earliest and most influential positivists was John Austin. In The Province of Jurisprudence Determined, Austin (1832) defined law simply as the command of a sovereign, which is backed by the threat of a sanction. The 'sovereign' is the person or body that is habitually obeyed by the bulk of society and which does not itself obey any other authority. In the UK, this could be seen as the ‘Queen in Parliament’. For Austin, whether a law is good or bad is irrelevant to its status as law; as long as the command comes from the sovereign and is backed by a threat, it is a valid law.
A more sophisticated and widely accepted version of positivism was developed by H.L.A. Hart in The Concept of Law. Hart (1961) criticised Austin’s ‘command theory’ as being too simplistic, as it fails to account for laws that confer powers rather than impose duties (like the law of contract). Hart described law as a system of rules, comprising primary rules (which forbid or require certain actions) and secondary rules (rules about the primary rules). The most important of these secondary rules is the "rule of recognition". This is a social rule accepted and used by legal officials (like judges and civil servants) to identify which rules count as valid laws within their legal system. In the UK, the rule of recognition is, put simply, "whatever the Queen in Parliament enacts is law" (Elliott and Quinn, 2020). Hart did accept that law and morality often overlap—what he called the ‘minimum content of natural law’, such as rules against violence, which are necessary for human society to survive. However, he insisted that this was a factual observation, not a necessary condition for a law's validity. A law that breaches this minimum content is still a valid law, though it may be a morally evil one.
The Hart-Fuller Debate: A Clash of Ideologies
The fundamental conflict between natural law and legal positivism is most clearly illustrated in their differing responses to unjust legal systems, such as that of Nazi Germany. This became the subject of a famous debate between Hart and Fuller in the late 1950s. The debate centred on how to treat the actions of people who had acted in accordance with Nazi laws, which were procedurally valid at the time but were horrifically unjust.
Hart, representing the positivist position, argued that the Nazi rules were indeed laws, despite their immorality. He believed it was confusing and dishonest to deny them the status of law. Instead, he argued that one should acknowledge their legal validity but then decide, on moral grounds, not to obey or enforce them. The clearer approach, for Hart, is to say, "This is law, but it is too wicked to be obeyed". To simply say it is "not law" hides the difficult moral choice that needs to be made.
Fuller, from a natural law perspective, strongly disagreed. He argued that the Nazi regime's system of governance was so lacking in the 'inner morality of law'—it was so arbitrary, secret, and discriminatory—that it could not be called a legal system at all. The rules were not just wicked laws; they were a perversion of law itself. This view was shared by the German jurist Gustav Radbruch, who post-war declared that if positive law is "intolerably unjust", it ceases to be law. This "Radbruch Formula" was used by post-war German courts to prosecute individuals who had committed crimes while claiming they were just following orders under Nazi law, demonstrating the profound real-world implications of this theoretical debate.
Relevance in the English Legal System
In practice, the English legal system is predominantly positivist in its orientation. The core constitutional doctrine of Parliamentary sovereignty is a classic positivist concept. It holds that an Act of Parliament is the highest source of domestic law and that the courts cannot invalidate it on the basis that it is unfair, irrational, or immoral (Bingham, 2011). If Parliament passes a law following the correct procedure, judges must apply it. For example, in R v Jordan (1967), the court upheld the Race Relations Act 1965 against a challenge that it violated freedom of speech, showing a commitment to applying the law as enacted by Parliament.
However, elements of natural law thinking can still be seen. The principles of natural justice in administrative law (now often referred to as procedural fairness), such as the right to a fair hearing, reflect Fuller’s ideas about the procedural morality necessary for a functioning legal system. Furthermore, the Human Rights Act 1998 requires UK courts to interpret legislation, as far as possible, in a way that is compatible with the rights set out in the European Convention on Human Rights. This Act effectively incorporates a set of moral values into English law, forcing judges to evaluate statutes against these standards and thus constraining pure parliamentary sovereignty. This suggests that while positivism describes the formal structure, a concern for justice and fairness, akin to natural law principles, influences how that structure operates.
In conclusion, natural law and legal positivism offer two fundamentally different answers to the question "what is law?". Legal positivism, with its separation of law and morality and its focus on the source of legal rules, provides a clear and functional account of how law is recognised and applied in a modern, stable legal system like that of England and Wales. However, natural law's insistence that law must have a moral purpose serves as a crucial critical tool. It reminds us that legality is not the only standard by which to judge a rule, and it provides a theoretical basis for resisting and condemning legal systems that become instruments of profound injustice. The continuing tension between the two theories shows that the relationship between law and morality remains one of the most important and unresolved questions in the study of law.
References
Austin, J. (1832) The Province of Jurisprudence Determined.
Bingham, T. (2011) The Rule of Law. Penguin.
Elliott, C. and Quinn, F. (2020) English Legal System. 21st edn. Pearson.
Fuller, L. (1969) The Morality of Law. Revised edn. Yale University Press.
Hart, H.L.A. (1961) The Concept of Law. Oxford University Press.
Martin, J. (2017) The English Legal System. 8th edn. Hodder Education.
R v Jordan [1967] Crim LR 192.
