Historically OR has conceived of itself as a professional practice giving rational, objective advice rooted in the ethos of science. However, the claim of science to rationality and objectivity has wilted under the onslaught of relativist and post-modern attack. One proposed philosophy of science seeks to avoid such problems by adopting a strictly objectivist approach. Critical rationalism (CR), the philosophy originated by Karl Popper, attempts to eliminate all inductive, justificatory and merely subjective claims by the ruthless application of deductive logic. The philosophical development of the CR approach to practice is currently a work-in-progress; however, it is an approach that should on the face of it find favour with OR, particularly for those who want to claim that OR is logically rational. The paper, drawing on the work of David Miller, explores how such an approach can be applied in the OR context. It concludes that although as CR suggests it may be possible to drive out inductive and justificatory claims in OR, subjective choice is an essential element of managerial decision-making and cannot be ignored or assumed away. The paper identifies some of the challenges that confront philosophers of practice if OR is to take the insights of CR to heart, suggests some possible responses, and identifies areas for future research.