 ‘Equality’ can be used in the very same sense both to describe and prescribe, as with ‘thin’: “you are thin” and “you are too thin”. The approach taken to defining the standard of comparison for both descriptive and prescriptive assertions of equality is very important (Oppenheim 1970). In the descriptive case, the common standard is itself descriptive, for example when two people are said to have the same weight. In the prescriptive use, the standard prescribes a norm or rule, for example when it is said people ought to be equal before the law. The standards grounding prescriptive assertions of equality contain at least two components. On the one hand, there is a descriptive component, since the assertions need to contain descriptive criteria, in order to identify those people to which the rule or norm applies. The question of this identification – who belongs to which category? – may itself be normative, as when we ask to whom the U.S. laws apply. On the other hand, the comparative standards contain something normative – a moral or legal rule, such as the U.S. laws – specifying how those falling under the norm are to be treated. Such a rule constitutes the prescriptive component (Westen 1990, chap. 3). Sociological and economic analyses of (in-)equality mainly pose the questions of how inequalities can be determined and measured and what their causes and effects are. In contrast, social and political philosophy is in general concerned mainly with the following questions: what kind of equality, if any, should obtain, and with respect to whom and when? Such is the case in this article as well.