So much of importance hinges on judgments about someone's rationality that it is nearly disgraceful how unclear we are about this concept. Judgments of irrationality are used to justify paternalistic intervention into people's lives and, as a result, mental institutions are replete with people who are in cages because their actions are ‘contrary to reason'. Furthermore, when someone engages in extremely dangerous or bizarre behaviour simply because he enjoys it, this is seen by many as proof of at least some degree of irrationality. The idea appears to be that imprudent acts are irrational.