The levelling down objection is the most serious objection to the principle of equality, but we think it can be conclusively defeated. It is serious because it pits the principle of equality squarely against the welfares of the persons whose welfares or resources are equalized. It suggests that there is something perverse about the principle of equality. In this paper, we argue that levelling down is not an implication of the principle of equality. To show this we offer a defence of, and partial elaboration of, what we call a common good conception of the principle of equality, which principle favours states in which everyone is better off to those in which everyone is worse off. We contrast this with what we call a purely structural conception of the principle of equality. The common good conception of equality involves two basic components: (1) in each circumstance there exists an ideal egalitarian distribution, which distributes equally all the available good in the distribution with the highest average welfare and (2) in evaluating how just the world is, it will matter how far the actual distribution is from the ideal distribution. The ideal egalitarian distribution in the circumstance is Pareto optimal and the approximation rule implies that Pareto superior states are less unjust than Pareto inferior states.
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