Natural law is a philosophical and jurisprudential concept holding that certain moral principles or legal norms are derived from nature, reason, or a higher order - and are universally binding on human beings independent of enacted or customary law. The precise source, content, and authority of natural law are subjects of longstanding dispute; definitions range from reason-based accounts rooted in classical philosophy to theological accounts grounding natural law in divine reason, to secular accounts locating it in human nature or evolutionary biology. Because the term carries distinct meanings across philosophical, theological, legal, and political contexts, its definition is itself contested - see natural-law-definition-debate for a structured treatment.
Natural law theory has been a continuous presence in Western moral and legal philosophy from antiquity through the present. Its classical formulation is associated with Aristotle's concept of a universal justice grounded in nature, and with Cicero's articulation of a right reason in agreement with nature. The tradition received its most systematic medieval treatment in Thomas Aquinas, who integrated Aristotelian natural philosophy with Christian theology, holding that natural law participates in the eternal law of God and is discernible through human reason.1) Aquinas's framework distinguishes the eternal law (God's rational governance of creation), natural law (the rational creature's participation in eternal law), human law (positive law derived from natural law), and divine law (revealed scripture).
During the early modern period, theorists including Hugo Grotius, Samuel Pufendorf, and John Locke reoriented natural law away from its explicitly theological grounding - Grotius famously suggesting natural law would hold etiamsi daremus non esse Deum (“even if we were to grant that God does not exist”) - toward a more secular, rationalist foundation.2) This development heavily influenced the constitutional and political thought of the American founding. The Declaration of Independence's appeal to “the Laws of Nature and of Nature's God” and to “unalienable Rights” is widely interpreted as drawing on this natural law tradition, though the precise philosophical commitments of the founders remain a matter of scholarly debate.3)
In the nineteenth and twentieth centuries, legal positivism - associated with Jeremy Bentham, John Austin, and H.L.A. Hart - challenged natural law by arguing that law and morality are conceptually separate, and that the validity of a legal rule depends on its social sources rather than its moral content.4) This debate between natural law and legal positivism remains central to contemporary jurisprudence. New Natural Law Theory, developed in the latter twentieth century by Germain Grisez, John Finnis, and others, has attempted to reconstruct natural law arguments on a non-theistic, reason-based foundation accessible to secular philosophical inquiry,5) though this project itself attracts criticism from both religious traditionalists and positivists.6)
Natural law arguments are invoked across a wide range of contemporary policy and legal debates, including discussions of constitutional interpretation, human rights, abortion, capital punishment, same-sex marriage, euthanasia, and international law. In the American conservative legal tradition, natural law - particularly in its Thomistic or founding-era forms - is frequently cited as grounding constitutional rights that positive law must not transgress.
Multiple distinct positions on natural law's foundations, content, and authority are represented in contemporary philosophy, theology, and jurisprudence.