Abstract

Thick ethical concepts are characterized by having both a “world-guided”/descriptive and an “action-guiding”/prescriptive aspect. The purpose of this paper is to argue that if we conceive of rationality as a thick ethical concept we will be able to understand two things. First, why people are inclined to believe that rationality – even if defined in terms of rational requirements – actually is normative. The action-guiding aspect of the concept of ‘rationality’ is responsible for this. It is highlighted for example by the fact that accusing somebody of behaving irrationally works as a stand-alone criticism of an action or actor. Second, we can also understand why those recent arguments by Broome and Kolodny trying to show just how rationality is normative fail. They are proceeding solely based on a world-guided definition of rationality. This does not lead to a misapplication of the concept stricto sensu; but to a thin concept which necessarily fails to grasp the evaluative force of the concept of ‘rationality’. This is particularly insightful for economists who often tend to use ‘rationality’ as a standard for judging behavior.