Subsidiarity is often implicitly conceived as an organizational model or a Weberian ideal type. The purpose of this paper is to show that, in contrast, subsidiarity is a principle in the sense of the tradition originating from Thomas Aquinas. Considered as an ideal type, subsidiarity may be perceived as impossible to apply because of its ideal status, abstracted from the circumstances. Here, we will demonstrate the consequences of the fact that subsidiarity is one of the common principles of practical moral (...) reasoning of particular prudence. Because it is a principle, subsidiarity does not have a visualizable substance or prescribe an organizational model, unlike the ideal type. It thus avoids the indiscriminate application of organizational models to contexts that are not appropriate, and in the context of tension between external consultants and managers, it rehabilitates the prudence of leaders who know the circumstances of their organization. (shrink)