Definition for natural law


First this paper will provide a definition for natural law. Second this paper will explain the principles behind this legal theory. Third this paper will compare and contrast this perspective with the view put forward by Hart in this book Concept of Law (1961). Fourth, this paper will describe and justify the merits of Hart's definition. Last this paper will conclude it findings.

Definition For Natural Law

Natural law is not one single legal theory and the term natural law covers a large number of writers across a large historical period. In this essay it is therefore necessary to produce a short-hand or summary understanding of theory of natural law for the purposes of highlighting the key elements of the theory of HLA Hart. For these purposes it is useful to contrast natural law and positivist legal theories, in reaction to each of which Hart was writing.

Both natural law and legal positivism are theories of the relationship between the “is” and the “ought” operative in any legal system. At a very basic level natural law and positivism are distinguished in the sense that natural law derives legal obligations from a higher moral, ethical or religious norm. In this sense, natural law does not distinguish between law and morality. As Finch puts it, “the central claim of a theory of a law of nature is that what naturally is, ought to be. The Is implies the Ought as a necessary consequence of its existence.” Finch goes on to note:

“A central proposition of natural law doctrines is that the law of nature ought to be the governing law for all things and all activities, including mankind and human relations. The fundamental hypothesis or assumption behind this approach is that there is a law or a body of laws which governs all things, whether these be gravity, motion, physical and chemical reactions, animal instincts or the actions of man …. Natural law theory supposes that there is a ‘law' (or set of principles) of nature according to the tenets and principles of which all things, including man himself, ought to behave.”

The primary attraction of natural law to the modern thinker is that it makes room for the argument that there may in some circumstances be a higher duty than mere obedience to the laws of the state. Such an argument has been raised intermittently throughout history, but featured largely in the Nuremberg War Crimes Trials and so re-awakened interest in the natural law philosophy. Some human rights theories and charters also have a strong natural law basis.

It is possible to say, within a natural law context, that an immoral law is not in fact a law, because the supposed “law” does not correspond to the higher natural law. But it is impossible to say this from within a positivist perspective. The essence of positivism is the rejection of any higher metaphysical sense of a legal “ought”. As Finch puts it:

“Legal positivism certainly does not involve a rejection of the Ought in a moral sense as a subject unworthy of study or unrelated to law. It does, however, involve an explicit rejection of the Ought in a metaphysical sense as the direct product of a metaphysical non-positive Is. The Is of legal positivism consists in the existence of man-made law and its methods of study are strictly confined to this sphere of existence.”

Hence many positivists subscribe to the view that any “law”, no matter how unjust or immoral, is binding if it complies with a test of formal legal validity applying within the legal system in question. For example, a common example (first made by Dicey) is that the UK Parliament could validly enact a law ordering the execution of all blue-eyed babies, and that such a law would be valid and binding despite its barbarity or immorality.

Contrast With Hart's Theory Of Natural Law

Hart was writing in response to the theory of legal positivism developed by John Austin, who believed that law was the command of the sovereign, irrespective of its moral content. In his book “The Concept of Law” Hart developed a theory of a legal system as consisting of primary and secondary rules. Primary rules are the existing set of operative legal obligations imposing rights and duties on subjects. Secondary rules are rules regulating how primary rules are made and changed, including a rule of recognition, rules of changes, and rules of adjudication.

Hart's definition of classical natural law comprises two distinct elements: “[1] there are certain principles of human conduct, awaiting discovery by human reason, [2] with which man-made law must conform if it is to be valid.” Hart was willing to make a limited concession to the first element, writing that there was a minimum content of natural law which had a “core of good sense”, but did not accept the second thesis, that law which does not correspond to natural law is invalid.

Hart was unwilling to accept grandiose conceptions of the end of humanity which might form the basis of natural law, but did identify a “minimum content of Natural Law” derived from five truisms of human nature, each related to the desire of a human being to survive: (1) human vulnerability, (2) approximate equality, (3) limited altruism, (4) limited resources, and (5) limited understanding and strength of will.

Hart thought that it was possible to derive a “core of good sense in the doctrine of Natural Law” from these essential facts of human existence. This core of good sense revealed the following about the relationship between law and morality: (1) the coercive authority of the state rests on an assumption, internalised by at least some subjects, of the “moral value of the system”, (2) the principles of legal validity in any legal system will often explicitly incorporate substantive or moral principles, as for example in the United States, (3) the interpretation of legal rules by courts will often incorporate moral reasons, (4) moral reasoning forms the basis of much criticism of legal rules, and (5) the application of objective, generally binding rules to human conduct, irrespective of the content of those rules, is at least “the germ” of justice.

On the question of whether validly enacted legal rules which offended morality were properly described as “laws”, Hart felt that “nothing is to be gained in the theoretical or scientific study of law as a social phenomenon” by making such an exclusion. In his later work “Positivism and the Separation of Law and Morals” Hart stated:

“Proof that the principles by which we evaluate or condemn laws are rationally discoverable, and not mere ‘fiats of the will', leaves untouched the fact that there are laws which may have any degree of iniquity or stupidity and still be laws. And conversely there are rules that have every moral qualification to be laws and yet are not laws.”

Criticism Of Hart's Theory

Hart's work has been the subject of enormous commentary. His work has criticised on the basis that he did not personally have first-hand knowledge of the classical theorists of natural law, and thus misunderstood the classical law tradition, particularly the second element of his definition of natural law (that for law to be binding it must conform to the higher moral law). To be fair to Hart, it is necessary to understand him as a social scientist who was attempting to build a theory of legal systems based on his observations of the world as it is. From this perspective, I think that Hart's attempt to draw out a bare minimum content of natural law from his observations regarding the basic vulnerability of humanity, and the need of humanity to survive, deserves some credit. It seems clear to me that humans are basically vulnerable and confronted by a need to survive in a world of scarce resources.

However, Hart's solution to the problem of whether natural law, even when described in this minimalist fashion, is binding, is not convincing. In my opinion, if one were to accept Hart's definition of a law as a primary rule which is binding on a subject according to a secondary “rule of recognition”, and at the same time accept his notion of the minimum content of natural law, then there must be some internal limits on how far a law could go before it ran up against the minimum content of natural rights, and that limit would be the point where a subject could legitimately refuse to obey the law, because to do so would put his or her own survival at stake. While it might be argued that the duty to obey is logically distinct from the formal validity of a legal rule within Hart's system of primary and secondary rules, I don't think that the duty of a subject to obey a law can be separated in any practical or meaningful way from the “validity” of that law.


In my opinion Hart's reformulation of natural law theory as having a minimum content derived from certain brute facts of human existence and the human need to survive seems to be in conflict with his rejection of the second element of natural law i.e. that human law must conform to the higher moral law if it is to be binding.


Dicey, AV, Introduction to the Study of the Law of the Constitution, online edition available at

Finch, J, (1979) Introduction to Legal Theory, Sweet & Maxwell, London

Finnis, J, (1980) Natural Law and Natural Rights, Clarendon Press, Oxford

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

Hart, HLA, (2003) “Positivism and the Separation of Law and Morals”, in Patterson, D, Philosophy of Law and Legal Theory: An Anthology, Blackwell Publishing, Oxford, pp69-90

Ivison, D (2008), Rights, Acumen, Stocksfield

Orrego, C, (2004) “H.L.A. Hart's Understanding of Classical Natural Law Theory”, 24 Oxford Journal of Legal Studies 287