The paper argues the underlying reasons of personal progressive income tax, showing how compensatory arguments were used to counterbalance the regressive effects of indirect taxes, which put a great burden on the poors, and how the theory of "sacrifice" felt by the taxpayers was the keystone for treating everyone as equals. Tax systems, in Italy as else-where, have nevertheless evolved out of the theoretical scheme of progressive income tax: it should apply to comprehensive income, but in fact it applies only to "earned" income. The result is an heterogeneous mix of special proportional taxes on capital incomes, while progressivity is bound to labour income. That’s why giving up with graduated rates, in fa-vour of a flat tax with exemption of basic income, could fulfill horizontal equity principle and ease off the working class.
Keywords: Progressive Taxation, Flat Tax, Personal Income Tax, Comprehensive Income, Horizontal Equity