Fairness and the proportionality principle

How should income be distributed in a way that respects both the egalitarian ideal that inequalities due to differences in opportunities should be eliminated and the liberal ideal that people should be free to pursue their own idea of the good life without interference from society? We show that reasonable interpretations of the egalitarian and the liberal ideal characterize what we refer to as the generalized proportionality principle. This principle states that an individual should have the share of total income that he or she would have had if everyone had the same opportunities and these opportunities were given by the average of the pre-tax income functions of all individuals in society. We argue that a redistribution mechanism based on this principle would eliminate unfair inequalities and preserve fair inequalities, and discuss when the generalized proportionality principle is equivalent to the simple proportionality principle.