For nearly three decades, the U.S. Supreme Court has struggled with the proper treatment of administrative action that departs from agency precedent. Moving toward a stronger theoretical account of administrative change requires exploring an underappreciated feature of all administrative action: the agency’s chosen mode of reasoning. Agencies sometimes execute their regulatory mandates by weighing evidence, utilizing technical expertise, and making value judgments in a process reflecting what we refer to as prescriptive reasoning. At other times, agencies employ a more expository form of reasoning grounded in analysis of congressional intent or the constraints imposed by relevant judicial opinions. While prescriptive reasoning yields conclusions about optimal and responsive policy, expository reasoning exhibits a driving concern with what the law is. That distinction, combined with modern administrative agencies’ powers to render official pronouncements about the meaning of legal texts, activates fundamental rule-of-law interests that should limit an agency’s discretion to deviate from precedent by invoking expository arguments—in other words, by declaring that a legal pronouncement which meant X yesterday means Y today. This Article proposes a new theory and doctrine of administrative change that affords substantial deference where change is driven by prescriptive reasoning, but requires de novo scrutiny of reversals grounded in expository reasoning. The proposal strikes an appropriate balance between the need for agency flexibility and the paramount importance of a stalwart, vibrant rule of law.