The tradition in moral and political philosophy holding that there exists a moral order discoverable through reason, independent of human legislation, that grounds universal rights and obligations — developed from Stoic and Roman sources through Aquinas's theological synthesis, adapted by Grotius and Locke into the foundations of international law and constitutional government, and contested by legal positivism, which holds that law is whatever human institutions make it.
Natural law is the claim that some things are wrong regardless of what any government says — that there are moral rules written into the structure of human nature and discoverable by reason, to which human law must answer. This claim has grounded arguments for the rights of indigenous peoples against colonial conquest, for civil disobedience against unjust laws, for the Nuremberg trials' assertion that following orders was no excuse, and for contemporary human rights law. It has also been used to resist women's equality, to justify racial hierarchy, and to block legal change on the grounds that nature has already decided. The power of natural law is that it places morality above politics. The danger is that whoever controls the interpretation of nature controls what morality permits.