Legal Unreasonableness: In Need of a New Justification?

Over the past decade, the High Court of Australia has made significant changes to the administrative law ground of unreasonableness, yet has given few indications of what values and functional considerations precipitated this shift. This is not unusual. The High Court has a reputation for preferring rules-based reasoning to values-based reasoning in administrative law (and beyond). But this does not mean that values and functional considerations are not important in shaping, and in explaining, the new legal unreasonableness test. This article analyses the changes that have occurred in unreasonableness – both in rhetoric and in application – and seeks to illuminate what this says about, and means for, Australian administrative law values. It explores the return, in the rhetoric of some judges, to relying on abuse of power as a justification and threshold for unreasonableness, and argues that other administrative law values better explain the new legal unreasonableness test.