Natural Law vs. Legal Positivism: Two Ways of Understanding Law

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Natural law and legal positivism are two theories of how law relates to morality. Natural law connects law to moral reason and the common good. Legal positivism says a rule is law because of how it was made and whether officials recognize it, and that a law’s merits do not determine whether it exists.

An unjust law is the test case. In his April 16, 1963, Letter from Birmingham Jail, Martin Luther King Jr. argued that a person who breaks an unjust law openly and accepts the penalty is expressing the highest respect for law. The two theories explain differently what authority such a law has and whether a person must obey it; neither demands obedience at any cost.

A law can be valid and still be unjust

Legal positivism holds that the existence and content of law depend on social facts, rather than the law’s merits. The relevant facts include the legislative enactments, judicial decisions and customs that a system’s officials recognize as authoritative. The first question is therefore institutional: what makes this rule part of this legal system?

This position does not treat justice as unimportant; it separates a law’s merits from the question of whether the law exists. A rule can meet the system’s criteria without becoming admirable, and a desirable policy does not become law merely because it is desirable. Legal validity, meaning a rule’s standing within the system, should not be confused with moral authority, meaning a justified claim to guide action.

Natural-law theory can also acknowledge a rule as legally valid by its social sources while judging it too unjust to obey or apply. Thomas Aquinas (1225 to 1274) was an Italian philosopher and theologian. Thomas Aquinas, the natural-law thinker King cites, never says simply that an unjust law is not law; he says it is not straightforwardly law, or is a perversion of law. So the disagreement cannot be reduced to one school noticing that governments make rules and the other refusing to notice.

What natural law connects to morality

Natural-law theory places positive law, the law established by human institutions, within practical reasoning about justice, peace and human wellbeing. Practical reasoning is reasoning about what to do, rather than merely about what has happened or what an official has ordered.

Aquinas defines law as an ordinance of reason for the community’s common good, promulgated, or made public, by the person or body responsible for that community. Under that definition, authority alone is not enough: the rule’s purpose and its appeal to reason matter too.

In Aquinas’s account, legislators have wide moral freedom to choose among alternative legal arrangements, and the one they adopt becomes legally and, presumptively, morally binding. That is a role for human judgment and lawmaking, not a claim that every legal detail can be read directly from a universal moral principle.

The Aquinas account distinguishes law addressed to human reasoning and choice from the physical and biological laws of nature. Natural law in this debate is therefore not a rule that whatever happens in nature is automatically right.

On Aquinas’s account, people can understand and follow the principles of practical reason and morality without regarding them as an appeal from a divine mind. Religious explanations can belong to the tradition without making a religious premise necessary for every moral argument it offers.

What legal positivism asks instead

The English jurist John Austin separates the question whether a law exists from the question whether it meets a standard of merit. That separation makes it possible to describe an institution’s rules without endorsing those rules.

Austin’s command theory describes laws as general orders from a sovereign, backed by a threat of force or sanction. The sovereign in this account is a person or group that most others obey and that does not similarly obey anyone else. This makes the pattern of command and obedience the central explanation of law, rather than the ruler’s moral right to rule.

A difficulty for command theories is that rules allowing people to make wills and contracts grant power and autonomy, rather than simply punish wrongdoing. A will-making rule does a different job from a prohibition: it provides a way to bring a legal result about. Reducing both jobs to threatened punishment loses that distinction.

H.L.A. (Herbert) Hart (1907 to 1992) taught philosophy at Oxford and later held its chair of jurisprudence. Hart, another positivist, instead rests a legal system’s ultimate test of validity on a social rule that its officials actually practice. He calls it the rule of recognition, and it sits alongside rules about who decides disputes and how laws may be changed. The question becomes what officials accept as the standards they must use, not merely whose orders people fear.

Legal positivism is not the doctrine that law is always clear and must be mechanically applied regardless of its merits. Knowing where legal authority comes from does not eliminate disagreement about what an authoritative text means.

Why moral principles remain part of the dispute

Some laws tell judges to reason morally. The U.S. Constitution’s ban on cruel and unusual punishment is an example: in deciding which punishments are lawful, judges are told to take morality into account.

Positivists disagree about what that means. Inclusive positivists say moral considerations become part of the law because the system’s recognized sources make them so. Exclusive positivists say such a law only refers to moral principles, and that law itself stops at its social sources. Both positions can recognize that a judge reasons morally; they explain the legal status of that reasoning differently.

Ronald Dworkin (1931 to 2013) was a legal philosopher. Ronald Dworkin challenges positivism by arguing that judges often rely on principles of justice and fairness that social or conventional rules cannot explain. He also argues that officials routinely dispute the basic criteria of legal validity in their own system. If officials disagree about which standards count as law, pointing to agreement among officials cannot by itself explain the dispute.

An unjust law tests the distinction

King was arrested in Birmingham on April 12, 1963, after defying a court injunction against protests during the campaign against segregation. A city ordinance required a permit for public demonstrations on city streets, and a state court had ordered the protesters not to hold them. King wrote his 1963 letter while confined in the Birmingham city jail. In it, he distinguishes a just law that uplifts human personality from an unjust law that degrades it. He draws on Aquinas’s moral standard for human law and argues that segregation laws are unjust because of their degrading effects. His standard judges what a rule does to people, rather than stopping at the fact that an authority has adopted it.

King argues that an unjust law should be broken openly and lovingly, with a willingness to accept the penalty. Accepting imprisonment, in his argument, can arouse the community’s conscience about an injustice while expressing respect for law. Resistance here is a public moral claim with a specified discipline, not a declaration that personal dislike makes every rule disappear.

Positivists do not have to believe that the law must always be obeyed. Hart says law may create a presumptive duty to obey that is limited by fairness, so there is no obligation to obey unfair or pointless laws. Joseph Raz (1939 to 2022) was a legal philosopher. Joseph Raz goes further and denies even a presumptive duty to obey the law, including in a just state. For a positivist, calling a rule law describes its institutional standing; it is not a final answer to King’s moral challenge.

In Aquinas’s account, laws that are unjust in certain ways lack moral authority, yet they can sometimes still oblige a person in conscience, but only so far as disobeying would cause disorder or set an example that leads others into wrongdoing. Neither tradition amounts to an automatic instruction to obey everything or to disobey whatever seems unjust.

Where these ideas meet U.S. government

The Declaration of Independence, dated July 4, 1776, describes unalienable rights endowed by a Creator and governments established to secure them. It says governments derive their just powers from the consent of the governed. That language places a standard of legitimate government beyond the mere fact that a ruler holds power.

The Declaration claims a right to alter or abolish government that destroys those ends, while warning against changing established government for light and transient causes. It does not supply a substitute for every institutional rule that a government needs.

The Constitution’s supremacy clause identifies the Constitution, federal laws made in pursuance of it, and treaties under U.S. authority as supreme law. It binds state judges to that authority despite conflicting provisions in state constitutions or laws. The Constitution also requires federal and state legislative, executive and judicial officials to support it by oath or affirmation. These provisions rank the sources of legal authority and bind officials to them, so a legal question is not settled by moral conviction alone.

Article V provides amendment procedures: proposals come from two thirds of both houses of Congress or a convention called on applications from two thirds of state legislatures. Ratification requires three fourths of state legislatures or state conventions, with Congress choosing the ratification mode. The process makes change part of the legal system itself. The founding documents therefore illustrate why moral justification and recognized legal procedures can matter at the same time, without assigning the entire U.S. system to one philosophical school.

How to compare the theories without confusing them

For natural law, the challenge is connecting legal authority to defensible moral reasons without treating a preferred answer as a complete legal code. John Locke (1632 to 1704) was a philosopher and political theorist. One objection, which John Locke addressed, is that natural law cannot be discovered, because not everyone who has reason knows it and people disagree about its content. Locke replied that having reason is not the same as using it. That reply defends the possibility of moral knowledge; it does not supply a procedure for settling every dispute. If the moral standard is disputed, making it a test of law raises a further question: whose account of that standard should an institution accept?

For positivism, the challenge is explaining how socially grounded rules account for moral principles and disagreement within legal practice. An account that explains why a rule is recognized has answered an important question, but it has not automatically answered every question about justice or resistance.

Philosophers disagree about the grounds of a moral obligation to obey, and some deny that even a reasonably just legal system has all the authority it claims. Law’s official voice can tell people what a system demands; whether that demand deserves their allegiance still requires an argument.