The common law of judicial review of administrative action has treated broad discretionary powers in an impressively robust way, refusing to permit the existence of unfettered regulatory discretion, instead imposing boundaries of acceptability on potentially abusive official conduct. But what has been a success in the area of administrative law has become a pathology in constitutional law. When charged with ensuring that government action is “prescribed by law” – that is, foreseeable and predictable – common law courts’ tendency to ensure that discretionary powers have at least some limits has caused them to permit the use of extremely broad powers. On the logic of the common lawyer, although the powers are extremely broad, they are not unfettered and must as a result be “prescribed by law”. In the area of government surveillance, however, the common law approach is inadequate – and sometimes, unfortunately smug: broad powers are often used secretly, in ways that are neither foreseeable nor predictable. To meet these inadequacies, common lawyers need to show some humility, by devising methods of ensuring predictability and foreseeability in governmental action that transcend the boundary between administrative law and constitutional law. These methods, which rely in part on the use of soft law and on imposing a robust requirement of reasonableness on official action, can properly be described as public law, as they are unique neither to administrative law or constitutional law and thus free of the pathology mentioned above.