Introduction
The debate between H.L.A. Hart and Lon L. Fuller, which unfolded in the pages of the Harvard Law Review in 1958, is a cornerstone of modern jurisprudence. It represents a classic clash between legal positivism and natural law theory, centring on the fundamental question of the relationship between law and morality. The debate was sparked by the legal and moral problems arising from the Nazi regime in Germany, particularly how a new legal system should deal with the legacy of "evil laws". This essay will explain the core arguments of both Hart and Fuller. It will first outline Hart's positivist defence of the separation of law and morals, before examining Fuller's response, which insists on a necessary "inner morality" of law. By analysing their disagreement over the "grudge informer" case, this essay will show the practical implications of their theories. It will conclude that while Fuller’s perspective has strong moral appeal, Hart's positivism provides a clearer and more practical framework for defining and identifying law.
Hart’s Legal Positivism and the Separation Thesis
H.L.A. Hart was a leading proponent of legal positivism. The central idea of his theory is the "separation thesis": the assertion that there is no necessary connection between law and morality (Hart, 1958). For Hart, the question of what law is must be kept separate from the question of what law ought to be. A law does not cease to be a law simply because it is considered morally wrong. The validity of a law within a particular legal system depends on whether it has been created in accordance with the rules of that system, not on its moral content.
Hart argued that mature legal systems are characterised by a union of primary and secondary rules. Primary rules are those that impose duties or grant powers to citizens (e.g., the criminal law), while secondary rules are rules about the primary rules themselves (Wacks, 2020). The most important of these is the "rule of recognition," a social rule accepted by officials that specifies the criteria for legal validity in a given system. For example, in the UK, the rule of recognition would identify Acts of Parliament and judicial precedents as valid sources of law. A law is legally valid if it meets these formal criteria, regardless of its justice or injustice.
Applying this to the problem of Nazi laws, Hart contended that these statutes, however morally reprehensible, were legally valid at the time because they were enacted according to the rules of the Nazi legal system. He acknowledged that citizens might face a moral dilemma: a law may be legally valid, yet so evil that there is a moral duty to disobey it. However, he insisted that this is a moral, not a legal, question. To deny the legal status of Nazi statutes simply because they were immoral would be to confuse the distinction between law and morality. Hart (1958, p. 618) believed this confusion would lead to intellectual dishonesty, suggesting it is clearer to say, "This is law; but it is too wicked to be obeyed."
For dealing with those who had acted under these evil laws, such as the "grudge informers" who used Nazi statutes to settle personal scores, Hart proposed a stark but honest solution: retrospective legislation. He argued that if the post-war state wanted to punish these individuals, it should do so by passing a new law that retroactively criminalised their actions. While Hart admitted that retrospective law is itself an undesirable thing, he believed it was the lesser of two evils. It would be a transparent moral and political choice made by the new legislature, openly confronting the moral problem instead of pretending that the Nazi laws were never "law" in the first place (Hart, 1958, p. 619).
Fuller’s Natural Law and the “Inner Morality of Law”
Lon L. Fuller provided a robust challenge to Hart’s position from a natural law perspective. Fuller rejected the positivist separation thesis and argued for a necessary connection between law and morality. However, his was a procedural, rather than substantive, natural law theory. He was not primarily concerned with the moral content of individual laws but with the moral quality of the system that produces them. He proposed that for a system of rules to be properly called a "legal system," it must adhere to a set of principles which he termed the "inner morality of law" (Fuller, 1958).
Fuller (1958, p. 645) outlined eight principles that constitute this inner morality. A legal system must have rules that are: (1) general, (2) publicly promulgated, (3) prospective (not retrospective), (4) clear and understandable, (5) not contradictory, (6) not impossible to obey, (7) reasonably stable over time, and (8) administered in a way that is congruent with the rules as announced. A total failure in any one of these principles, or a substantial failure across several, would mean that the system is not merely a "bad" legal system, but not a legal system at all. It is a system of arbitrary power, not of law.
From this perspective, Fuller argued that the Nazi regime, particularly in its later years, had so fundamentally violated these principles—through secret laws, retroactive statutes, and a complete disregard for consistency—that it had forfeited its claim to be a legal system. The rules it produced were not "law" in any meaningful sense. Therefore, the Nazi statutes under which grudge informers acted were legal nullities.
This leads to a different solution to the post-war problem. According to Fuller, a post-war court would not need retrospective legislation to punish the informer. The court could simply find that the Nazi statute provided no legal defence because it was not a valid law to begin with. The woman was not acting under the authority of "law" but was taking advantage of a system of terror. Fuller (1958, p. 660) argued that this approach maintains fidelity to law by recognising that the essential requirements of legality had been abandoned by the Nazi regime. It avoids the moral compromise of using retrospective legislation by denying legal status to the evil system from the outset.
A Comparison of the Two Positions
The "grudge informer" case, based on a real German court decision, brings the abstract debate into sharp focus. Hart sees the problem as a choice between two evils: letting the informer go unpunished or using a retrospective statute. He prefers the latter because it is open about its moral and political aims. Fuller, by contrast, sees no such dilemma. For him, the Nazi rule was not law, so the informer’s defence fails on legal grounds. The court is not creating a new crime; it is simply refusing to recognise the validity of the immoral "law" she relied on.
Fuller’s position has a powerful intuitive appeal. It provides a theoretical basis for resisting tyrannical regimes and aligns with the idea that law should serve justice. His eight principles of legality are also widely recognised as essential components of the modern concept of the rule of law (Ratnapala, 2017). However, a weakness in Fuller's argument is its potential for uncertainty. Deciding when a system has crossed the line from a "bad legal system" to a "non-legal system" is a subjective judgment. Who is to decide when the failure to adhere to the eight principles is substantial enough to nullify the entire system? This could give judges wide and unpredictable discretion to invalidate laws they find morally or politically objectionable, disguised as a legal ruling.
Hart’s positivism, while morally less comfortable, offers greater clarity and certainty. It provides a clear test for legal validity based on the rule of recognition. This prevents judges from invalidating laws based on their personal morality. The problem of evil laws is pushed into the political and moral arena, where Hart believes it belongs. His solution, retrospective legislation, is politically controversial but legally transparent. It forces a society to confront its past and make a conscious, public decision, rather than leaving the matter to the judiciary to resolve through a redefinition of "law".
In conclusion, the Hart-Fuller debate highlights a fundamental tension in legal theory between the certainty of law and its moral purpose. Hart’s positivism prioritises a clear, formal definition of law, separating it from the complexities of moral judgment. Fuller’s natural law theory insists that law cannot be divorced from morality and must meet certain procedural standards to be worthy of the name. While Fuller’s eight principles provide a valuable blueprint for a just legal order, his overall theory risks blurring the line between legal analysis and moral judgment. Hart’s approach, though it leads to difficult moral choices, ultimately offers a more stable and predictable account of what law is, thereby preserving the distinct character of legal obligation while still allowing for moral critique and, where necessary, civil disobedience.
References
Fuller, L.L. (1958) 'Positivism and Fidelity to Law – A Reply to Professor Hart'. Harvard Law Review, 71(4), pp. 630-672.
Hart, H.L.A. (1958) 'Positivism and the Separation of Law and Morals'. Harvard Law Review, 71(4), pp. 593-629.
Ratnapala, S. (2017) Jurisprudence. 3rd ed. Cambridge: Cambridge University Press.
Wacks, R. (2020) Understanding Jurisprudence: An Introduction to Legal Theory. 6th ed. Oxford: Oxford University Press.
