Hart’s first career was as a lawyer; he became Fellow and Tutor in philosophy at New College, Oxford (1945–52), then professor of jurisprudence at Oxford (1952–68), and Principal of Brasenose College (1973–8). He was the most influential legal philosopher of his time, whose book The Concept of Law (1961) set the agenda for a generation of jurisprudence. The work applies techniques from linguistic philosophy to a sophisticated defence of the view that law consists essentially in a system of rules located in social practices: a version of legal positivism. Hart also wrote, with A. M. Honoré, Causation in the Law (1959), a study of causation in questions of civil and criminal liability. A liberal in his political views, Hart became well known to a wider public through the debate with Lord Devlin over the Wolfenden report on the function of the law in the sphere of sexual behaviour, where his The Morality of the Criminal Law (1965) remains a classic defence of the liberal position on the limits of law in moral matters. Other works include Punishment and Responsibility (1968), Essays on Bentham: Jurisprudence and Political Theory (1982), and Essays in Jurisprudence and Philosophy (1983). The definitive biography is by Nicola Lacey (2004).