This paper provides an exposition and explanation of the various ways in which value judgements can be instilled into an income tax system, or, if inherent in a pre-existing one, can be drawn out and understood. A putative EUwide income tax, additional to the national income taxes of the Member States, is used as a vehicle for the analysis. When the identification of equals is done using an appropriate ‘equivalent income function’, and the equal treatment command modelled in terms of it, the resultant tax will in general be differentiated between countries. A supplementary command, “equal progression among equals”, can be achieved if equals are defined as those at the same percentile point in the withincountry distributions, and if these distributions differ in logarithms only by location and scale. Differentiated proportional taxes could even be equitable in this scenario, the flat rate being higher in less unequal countries. The value judgements implicit in a given tax system can be exposed in terms of an equivalence scale which is in general “base dependent”.
