Glossary
Natural law
The view that there is a moral order discoverable by reason that binds all people and against which human laws can be measured.
Also called: law of nature, natural law theory
Natural law is a tradition of moral and legal thought holding that certain moral principles are built into human nature and can be known by reason, regardless of what any legislature decrees. In this view, human law gets its authority from its conformity to that higher standard, and a law grossly contrary to it is unjust.
Its roots go back to Aristotle and the Stoics, and it was developed systematically by Thomas Aquinas, who held that humans share in God's eternal law through reason. It influenced the common law, the founders' ideas of natural rights and Martin Luther King Jr.'s argument in the "Letter from Birmingham Jail" that an unjust law is no law at all. Catholic social teaching continues to rely on it, as do some secular philosophers.
Natural law figures in debates about abortion, marriage, religious liberty and the limits of government. Many conservatives treat it as a foundation for objective morality and defend it against moral relativism. Critics argue that it is too vague or religious, that people disagree widely about what nature requires, and that legal positivism, which separates law from morality, describes legal systems better. It overlaps with ordered liberty.
Last reviewed November 8, 2026