Abstract: A requirement for public reasoning pervades the modern state. Much of the story of administrative law, indeed, might be understood as an effort to calibrate the requirement of bureaucrats to provide reasons for their actions. The dominant view among scholars and policymakers elevates the value of reason-giving, illustrated for example by a requirement for reason-giving in proposed bipartisan legislation to protect Special Counsel Mueller from politically-based removal. Yet legal and administrative “realists” have long doubted the efficacy of public reasons, and some argue we ought to be more tolerant of laxity in reasoning. Both central and contested, official reason-giving remains surprisingly unexamined empirically. Neither the boosters nor the skeptics have responsive evidence to support their positions that official reason-giving matters, or not. Drawing from the traditions of experimental economics, this article presents responsive evidence on this issue, reporting results from novel experiments that examine whether reason-giving reduces abuses of fiduciary responsibilities. The results from these exercises suggest that a requirement for reason-giving powerfully deters abusive behavior, notably increasing fidelity to fiduciary standards, but principally if reason-giving is subjected to reasonableness review, as through judicial review. The study informs on-going debates over the proper role of reason-giving and judicial review in the modern state.