The Principle of Legality

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. This theory makes sense of these cases in a way that prevailing theories do not, and provides us with satisfying answers to the difficult questions about legality outlined above. This includes answers to some of the most pressing and controversial questions in contemporary public law scholarship.