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Natural-law theory

Justifying the state's use of force to coerce compliance with its laws has proven a consistent theoretical problem. One of the earliest justifications involved the theory of natural law. This posits that the nature of the world or of human beings underlies the standards of morality or constructs them. Thomas Aquinas wrote in the 13th century: "the rule and measure of human acts is the reason, which is the first principle of human acts". He regarded people as by nature rational beings, concluding that it becomes morally appropriate that they should behave in a way that conforms to their rational nature. Thus, to be valid, any law must conform to natural law and coercing people to conform to that law is morally acceptable. In the 1760s, William Blackstone described the thesis:

But John Austin (1790–1859), an early positivist, applied utilitarianism in accepting the calculating nature of human beings and the existence of an objective morality. He denied that the legal validity of a norm depends on whether its content conforms to morality. Thus, in Austinian terms, a moral code can objectively determine what people ought to do, the law can embody whatever norms the legislature decrees to achieve social utility, but every individual remains free to choose what to do. Similarly, H.L.A. Hart saw the law as an aspect of sovereignty, with lawmakers able to adopt any law as a means to a moral end.

Thus the necessary and sufficient conditions for the truth of a proposition of law involved internal logic and consistency, and that the state's agents used state power with responsibility. Ronald Dworkin rejects Hart's theory and proposes that all individuals should expect the equal respect and concern of those who govern them as a fundamental political right. He offers a theory of compliance overlaid by a theory of deference (the citizen's duty to obey the law) and a theory of enforcement, which identifies the legitimate goals of enforcement and punishment. Legislation must conform to a theory of legitimacy, which describes the circumstances under which a particular person or group is entitled to make law, and a theory of legislative justice, which describes the law they are entitled or obliged to make.

There are natural-law theorists who have accepted the idea of enforcing the prevailing morality as a primary function of the law. This view entails the problem that it makes any moral criticism of the law impossible: if conformity with natural law forms a necessary condition for legal validity, all valid law must, by definition, count as morally just. Thus, on this line of reasoning, the legal validity of a norm necessarily entails its moral justice.