Book Symposium | The Principle of Legality: A Moral Theory

A book symposium organised by the Quain Centre of Jurisprudence Speaker: Dr Conor Crummey, Assistant Professor in Law (Maynooth University, School of Law and Criminology) Chair: Prof George Letsas, Professor of Philosophy of Law (UCL Laws) About the Book Symposium: It is a well-known tenet of public law that judges must interpret a statute consistently with common law rights and principles, unless that statute uses clear and express language to license the violation of such rights and principles. This is the ‘principle of legality’. But which rights and principles trigger the principle of legality? How ‘clear and express’ must statutory language be to license interference with common law rights? Does this method of interpretation apply only to statutes, or should it apply to interpretation of the scope of prerogative powers as well? What does the method of interpretation tell us about the relationship between the rule of law and parliamentary supremacy? This book develops a philosophical theory of the principle of legality to help answer these questions. This book challenges the prevailing notion that the principle of legality is a presumption about the intentions of the legislature. Drawing on debates in the philosophy of language and general jurisprudence, the book shows that these theories fail to account for the principle of legality in a satisfactory way. The book then deploys a non-positivist theory of general jurisprudence to show that judges invoking the principle of legality are engaging in a complex process of moral reasoning. The Principle of Legality: A Moral Theory (OUP, 2025) About the Speaker: Conor Crummey is Assistant Professor in Law at Maynooth University School of Law and Criminology. Prior to that, he was Lecturer in Law at University of Glasgow and Queen Mary University of London. He completed his doctorate at UCL Faculty of Laws. His work focuses on the theoretical underpinnings of constitutional law, with a particular focus on the connections between general jurisprudence and statutory interpretation in UK public law. It also addresses fundamental debates in general jurisprudence, in particular the question of how we understand the relationship between legal obligations and genuine moral obligations. UCL 200: UCL200 marks the bicentenary of University College London — 200 years since our founding in 1826 and our legacy of pioneering education, research, and community. Throughout 2026, UCL will host a vibrant programme of events and activities celebrating our founding values, our global impact, our communities, and our vision for the future. Visit the UCL200 website to explore the full programme and learn how you can get involved. To see how UCL Laws is contributing to this landmark year — with events, stories, and initiatives highlighting two centuries of legal scholarship and impact — visit the UCL Laws UCL200 page. Photo by Nigel Hoare on Unsplash