This chapter introduces the central technical apparatus to describe official action and thus, also, to describe the mechanics of judicial review of official action implicit in the traditional terminology of ‘ultra vires', that is, acting ‘beyond one's powers'. Officials are reposed with powers in virtue of rules of two types, which I call rules of competence and rules of conduct. These are not just labels of convenience, they explain the constitution of office and the inherently legal and limited nature of official vires. They box out the ‘space’ in which an official (i) can and (ii) may act lawfully, which space I call ‘Spielraum'. This concept relates to a modified Hohfeldian schema of jural relations which removes the temptation of "residual liberties" as a valid category of the official legal position.

This chapter provides some more detail on the rules of competence and rules of conduct that empower officials to act as such and constrain the scope of their action. The logic of empowerment, and the fundamental distinction between ability and permission, provides a profound insight into the two traditional ‘limbs’ of the ultra vires rule – the ‘narrow’ limb concerned with competence, jurisdiction, or vires in the strict sense, and the ‘broad limb’ concerned with the manner, form, and purpose of an exercise of a competence that the official clearly does have. Not only does this provide a simple and powerful explanation for the ultra vires review of non-statutory executive powers; it provides the foundation for a general theory of judicial review based in the courts’ inherent (common law) jurisdiction to police the bounds of, and constraints upon, officials’ vires – whether statutory or non-statutory.