Pioneering the modern literature on heuristics in cognition, Amos Tversky and Daniel Kahneman contended that ‘people rely on a limited number of heuristic principles which reduce the complex tasks of assessing probabilities and predicting values to simpler judgmental operations’ (Tversky and Kahneman 1974: 1124). Intense controversy has developed over the virtues and vices of the heuristics, most of them ‘fast and frugal’, that play a role in many areas (Gigerenzer and Todd 1999; Gilovich et al. 2002). But the relevant literature has only started to investigate the possibility that in the moral and political domain, people also rely on simple rules of thumb that often work well but that sometimes misfire (Baron 1994). In fact the central point seems obvious. Much of everyday morality consists of simple, highly intuitive rules that generally make sense but that fail in certain cases. It is wrong to lie or steal, but if a lie or a theft would save a human life, lying or stealing is probably obligatory. Not all promises should be kept.