Priority, solidarity and egalitarianism

Using the axioms of “priority” and “solidarity” (solidarity in the influences of the changes in population or resources on the original members) in a variable and potentially infinite population model, Moreno-Ternero and Roemer (2006) establish an axiomatic characterization of index-egalitarian rules. We show that similar characterization results can be established in a fixed and finite population model, when their solidarity is replaced with the axiom of agreement. This axiom requires that when there is a change in agents’ characteristics (output functions) or total resources, all agents who remain unchanged should be influenced in the same direction: all unchanged agents get more, all get less, or all get the same amount as before. We also show that agreement can be replaced with the combination of resource monotonicity and separability and that the priority axiom in Moreno-Ternero and Roemer (2006) can be replaced with an alternative formalization of Parfit’s priority view.