Is Legal Positivism’s Separation Thesis Still Defensible

Despite the influential critiques of Lon Fuller and Ronald Dworkin, H.L.A Hart’s separation thesis remains defensible. Much of the debate surrounding the thesis stems from misunderstanding of what the thesis claims. While critics challenge the theory, their arguments rest on a conceptual error. Critics often conflate the influence of morality on law with its necessity. While moral values can guide lawmakers, they do not dictate the criteria for legal validity. Thus, Hart’s thesis can be viewed as a more modest claim, and once this distinction is drawn, the thesis remains defensible in a modified form. This distinction becomes clear when examining Fuller’s procedural critique directly.

Before focusing on the critiques, it is necessary to establish what Hart’s separation thesis asserts. Hart’s claim does not argue that law and morality are unrelated, nor does he argue that a well-functioning legal system reflects the moral values of society.[1] He states that “What law is from what the law ought to be”.[2] There is no necessary link between a rule being legally valid and morally correct. If a rule is made following the system’s rule of recognition, then it is still law, even if it is morally wrong.[3]

Hart also placed focus on the minimum content of natural law.[4] He delved into the idea of the most functioning legal systems placing bans on ideas such as violence, due to human vulnerability and need to live in cohesion. Hart never claimed law and morality are unrelated, he highlighted that moral merit is not a criterion of rules being ‘legally valid’.

Fuller’s response to Hart, argues that law possesses an ‘inner morality’. Alongside Dworkin, they both contend that for laws to be deemed just and legitimate, they must be rooted in moral principles.[5] Fuller raised eight rules which create a valid legal system, these being:[6]

1. Generality, meaning there must be rules or rules of law.
2. Publicity: rules made available for the public.
3. Retroactivity: retroactive laws which cannot be passed that punish past behaviour that was legal at the current time.
4. Clarity
5. Rules which do not contradict each other.
6. Practicability: laws must be written reasonably to allow people to be able to comply.
7. Consistency: laws must be stable and not constantly change.
8. Congruence: there must be congruence between the law as written and the law which is how it is declared.[7]

On this view, Fuller’s approach can be equally criticised. With using the Vagrancy Act 1824, which penalises individuals for circumstances which can be out of their control, this Act clashes with several of these principles.[8] These being the principles of practicability, clarity, congruence and generality. He places focus on the idea that law and morality do not need to be linked, and instead there should only be some normative standard. This would be morality being built into the law’s functioning and placing constraint on what can be considered to be valid law.

Nevertheless, this does not undermine Hart’s separation thesis. Fuller’s principles such as clarity, prospectivity and consistency are considered to be pre-existing conditions which are necessary for the functioning of the legal system. They help guide behaviour, rather than being inherently moral requirements. Fuller therefore, has not established a connection between morality and the law, he only showed the law can function more when its procedures are sound.[9]

Dworkin’s critique challenges Hart’s separation thesis more directly. Through the example of judges, he argues that Hart’s thesis fails to account for how judges decide hard cases. Rather than only relying on legal rules, courts often apply moral principles, and these can become binding.[10] Dworkin presented this through the case of Riggs v Palmer.[11] He presents many arguments. As Hart himself argued, the law consists of rules identified through social recognition, and where no rule applies judges can exercise discretion to create new law. Dworkin plainly rejected this. He contended even in difficult cases, judges do not invent new law, they apply existing legal principles which are already a part of the legal systems. This shows that legal validity does depend on moral soundness. He identified that the law in hard cases cannot be one without engaging in moral reasoning.

This can be seen to be a pressure point for the separation thesis. However, this does not mean that the separation thesis should be abandoned. This only means it should be refined. The fact that judges are able to treat moral principles as binding is a social factor of the legal system, rather than a necessary link between morality and law. This could link to the idea that morality has become relevant due to the system allowing it to become relevant, not because they are inseparable in general. This distinction defends the separation thesis.

The challenges which are posed by Fuller and Dworkin do not defeat the separation thesis presented by Hart. Fuller helps show that a functioning legal system satisfies certain procedural conditions, but regardless a system can still enact the eight principles and still create unjust law. This proves that this can create an effective legal system, rather than being a criterion of a valid law. Dworkin proves that judges in hard cases often reason from moral principles rather than principled law, which can reflect a social factor in the legal system not a connection between morality and law. These critics help show that morality can be relevant to legal validity, without proving that it must be relevant. Hart’s separation thesis therefore remains defensible when understood as he intended for it to be. This being not that law and morality are unrelated, but as the narrower claim that legal validity, does not depend on its moral merit.

To conclude,  the separation thesis, as Hart intended it to be, remains defensible. The critiques which this theory receives rest on the influence of morality on law, and its necessity to legal validity. However, the separation thesis still remains defensible, as it does not claim the law and morality are unrelated. It maintains that there is no necessary connection. Moral values may influence legislation and judicial reasoning, but Hart’s theory offers an account of legal validity, while acknowledging an influence of morality on law.

BIBLIOGRAPHY

CASES

Riggs v Palmer 115 NY 506 (1889)

BOOKS

Dworkin R, Taking Rights Seriously (Duckworth 1977)

Fuller L, The Morality of Law (rev edn, Yale University Press 1969)

Hart HLA, The Concept of Law (2nd edn, Oxford University Press 1994)

JOURNAL ARTICLES

Beehler R, ‘Legal Positivism, Social Rules, and Riggs v Palmer’ (1990) 9 Law and Philosophy [page]

Hart HLA, ‘Positivism and the Separation of Law and Morals’ (1958) 71 Harvard Law Review 593

Summers R, ‘”Is” and “Ought” in Legal Philosophy’ (1963) 13(51) Philosophical Quarterly 157

WEBSITES AND BLOGS

Geraghty L, ‘The Vagrancy Act: What Is It and Why Is It Being Scrapped?’ (The Big Issue, 2022) https://www.bigissue.com/news/housing/what-is-the-vagrancy-act/ accessed 9 July 2026

Golliher D, ‘What is the Philosophy of Law?’ (Maximum New York, 27 October 2023) https://www.maximumnewyork.com/p/fullers-eight-principles accessed 9 July 2026

LawTeacher, ‘Hart and Fuller Debate on Law and Morality’ (LawTeacher, 2021) https://www.lawteacher.net/free-law-essays/judicial-law/hart-and-fuller-debate-9262.php accessed 9 July 2026

[1] Hart, H.L.A,  The Concept of Law (2^nd edn, OUP 1994) ch 9.

[2] Hart, H. L. A,  Positivism and the Separation of Law and Morals (1958)

[3] Robert Summers, ‘“Is” and “Ought” in Legal Philosophy’ https://scholarship.law.cornell.edu/cgi/viewcontent.cgi?article=2423&context=facpub accessed 9 July 2026

[4] HLA Hart, The Concept of Law (2nd edn, Oxford University Press 1994) 193–200.

[5] Lon Fuller, The Morality of Law (rev edn, Yale University Press 1969)

[6] Daniel Golliher, ‘What is the Philosophy of Law?’ (Maximum New York, 27 October 2023) https://www.maximumnewyork.com/p/fullers-eight-principles accessed 9 July 2026.

[7] Ibid.

[8] Liam Geraghty, ‘The Vagrancy Act: What Is It and Why Is It Being Scrapped?’ (The Big Issue, 2022) https://www.bigissue.com/news/housing/what-is-the-vagrancy-act/ accessed 9 July 2026

[9] LawTeacher, ‘Hart and Fuller Debate on Law and Morality’ (LawTeacher, 2021) https://www.lawteacher.net/free-law-essays/judicial-law/hart-and-fuller-debate-9262.php accessed 9 July 2026.

[10] Ronald Dworkin, Taking Rights Seriously (Duckworth 1977)

[11] Rodger Beehler, ‘Legal Positivism, Social Rules, and Riggs v Palmer’ (1990) 9 Law and Philosophy