H. L. A. Hart

In The Concept of Law, published in 1961, Hart describes the rule of recognition as the social rule officials use to identify valid law. It is a central idea in modern legal positivism.

Hart argued that law is not just commands backed by threats from a sovereign. He distinguished primary rules of conduct from secondary rules about how legal systems create, change, and recognize law.

Hart and Lon Fuller debated the relation between law and morality in the late 1950s. Hart defended a positivist separation of legal validity from moral merit, while Fuller emphasized law's internal morality.

The book gives a compact framework for thinking about legal systems, obligation, and authority. It remains a starting point for debates between positivists, natural law theorists, and interpretivists.