Robespierre 7 · CC BY-SA 4.0

H. L. A. Hart reshaped twentieth-century legal philosophy with The Concept of Law, arguing that legal systems function through a "rule of recognition" rather than simple commands backed by force — the book that made him the leading exponent of modern legal positivism. During the Second World War he worked in British intelligence alongside Alan Turing, and as Oxford's Professor of Jurisprudence from 1952 he conducted a famous public debate with Patrick Devlin over whether law should enforce morality, and mentored the next generation of legal theorists, including Ronald Dworkin and Joseph Raz.