James Griffin (1986, 1997, 2000) and Ruth Chang (1997) have argued that alternatives (and values) can be comparable when it is neither true that one is better than the other, nor true that they are exactly equal in value. The relation which holds between them has gone under various names: the alternatives are ‘roughly equal in value’ (Griffin) or ‘on a par’ (Chang). In this paper, I give a formal analysis of this relation. This analysis allows us to distinguish between two slightly different notions of ‘at least as good as’. It is argued that the distinction between these notions is important for discussions of rationality, as is the distinction between ‘rough equality’ or ‘parity’ and incomparability.

Irrational people create problems not only for themselves and those around them, but also for those who study them. They cause trouble for social scientists because their actions are inexplicable, at least according to generally accepted models of explanation. Explanations in the social sciences normally assume the form of rationalizations: actions are explained by showing that, relative to what the subjects believe and desire, the actions were done for good reasons. Conversely, when good reasons cannot be found for why someone acted as they did, their behavior remains inscrutable. Irrational people, therefore, stymie social scientists because their actions do not reveal the rationality needed to produce adequate explanations.