Michele Lombardi

Liberal Egalitarianism and the Harm Principle

This paper analyses the implications of classical liberal and libertarian approaches for distributive justice in the context of social welfare orderings. An axiom capturing a liberal non-interfering view of society, named the Weak Harm Principle, is studied, whose roots can be traced back to John Stuart Mills essay On Liberty. It is shown that liberal views of individual autonomy and freedom can provide consistent foundations for social welfare judgements, in both the finite and the infinite context. In particular, a liberal non-interfering approach can help to adjudicate some fundamental distributive issues relative to intergenerational justice. However, a surprisingly strong and general relation is established between liberal views of individual autonomy and non-interference, and egalitarian principles in the Rawlsian tradition.

Partially-Honest Nash Implementation: Characterization Results

This paper studies implementation problems in the wake of a recent trend of implementation of non-consequentialist nature, which draws on the evidence taken from experimental and behavioral economics. Specifically, following the seminal works by Matsushima (2008) and Dutta and Sen (2009), the paper considers implementation problems with partially-honest agents, which presume that there is at least one individual in society who concerns herself with not only outcomes but also honest behavior at least in a limited manner. Given this setting, the paper provides a general characterization of Nash implementation with partially-honest individuals. It also provides the necessary and sufficient condition for Nash implementation with partially-honest individuals by mechanisms with some types of strategy-space reductions. As a consequence, it shows that in contrast to the case of the standard framework, the equivalence between Nash implementation and Nash implementation with strategy space reduction no longer holds.

Uncovered Set Choice Rules

I study necessary and sufficient conditions for a choice function to be rationalized in the following sense: there exists a total asymmetric relation T (a tournament) such that, for each feasible (finite) set, the choice set coincides with the uncovered set of T restricted to that feasible set. This notion of ‘maximization’ offers testable restrictions on observable choice behavior.

Natural Implementation with Partially-Honest Agents

The paper proposes necessary and sufficient conditions for the natural implementation of(efficient) social choice correspondences (SCCs) in pure finite exchange economies when some ofthe agents are partially honest. A partially honest agent is an agent who strictly prefers to tellthe truth when lying has no better material consequences for her. Firstly, it is shown that ifthere is even one partially honest agent in the economy (and the planner does not know heridentity), then any SCC is Nash implementable by a natural price-allocation mechanism. Secondly,and in sharp contrast with the results of conventional models of natural implementation, it isshown that the equivalence relationship between natural price-allocation mechanisms and naturalprice-quantity² mechanisms no longer holds. Finally, and even more strikingly, the paper reportsthat the class of implementable SCCs by natural price-quantity mechanisms is significantly enlarged.

Natural implementation with semi-responsible agents in pure exchange economies

We study Nash implementation by natural price–quantity mechanisms in pure exchange economies when agents have intrinsic preferences for responsibility. An agent has an intrinsic preference for responsibility if she cares about truth-telling that is in line with the goal of the mechanism designer besides her material well-being. A semi-responsible agent is an agent who, given what her opponents do, acts in an irresponsible manner when a responsible behavior poses obstacles to her material well-being. The class of efficient allocation rules that are Nash implementable is identified provided that there is at least one agent who is semi-responsible. The Walrasian rule is shown to belong to that class.

Partially Honest Nash Implementation:A Full Characterization

Given the framework introduced by Dutta and Sen (2012), this paper offers a comprehensive analysis of (Nash) implementation with partially honest agents when there are three or more participants. First, it establishes a condition which is necessary and sufficient for implementation. Second, it provides simple tests for checking whether or not a social choice correspondence can be implemented. Their usefulness is shown by examining implementation in a wide variety of environments.

Treading a Fine Line: Characterisations and Impossibilities for Liberal Principles in Infinitely-Lived Societies

Abstract This paper extends the analysis of liberal principles in social choice recently proposed by Mariotti and Veneziani (2009a) to infinitely-lived societies. First, some novel characterisations of inegalitarian leximax social welfare relations are derived based on the Individual Benefit Principle (IBP), which incorporates a liberal, non-interfering view of society. This is surprising because the IBP does not explicitly incorporate any preference for inequality, nor does it assign priority to well-off members of society. Second, some impossibility results are derived that highlight a general tension between standard fairness and efficiency axioms in social choice, and a liberal Principle of Non-Interference that generalises IBP.

Minimal Covering Set Solutions

We study necessary and sufficient conditions for a multi-valued solution S to be rationalized in the following sense: there exists a complete asymmetric relation T (a tournament) such that, for each feasible (finite) set, the solution set of S coincides with the minimal covering set of T restricted to that feasible set. Our characterization result relies only on properties relating S across feasible choice sets.

Natural implementation with partially-honest agents in economic environments with free-disposal

We study Nash implementation by natural price-quantity mechanisms in pure exchange economies with free-disposal (Saijo et al., 1996, 1999) where agents have weak/strong intrinsic preferences for honesty (Dutta and Sen, 2012). Firstly, the Walrasian rule is shown to be non-implementable where all agents have weak (but not strong) intrinsic preferences for honesty. Secondly, the class of e¢ cient allocation rules that are implementable is identi…ed provided that at least one agent has strong intrinsic preferences for honesty. Lastly, the Walrasian rule is shown to belong to that class.

Liberal Principles for Social Welfare Relations in Infinitely-Lived Societies

This paper extends the analysis of liberal principles in social choice recently proposed by Mariotti and Veneziani (2009a) to infinitely-lived societies. First, a novel characterisation of the inegalitarian leximax social welfare relation is provided based on the Individual Benefit Principle, which incorporates a liberal, non-interfering view of society. This result is surprising because the IBP has no obvious inegalitarian content. Second, it is shown that there exists no weakly complete social welfare relation that satisfies simultaneously the standard axioms of Finite Anonymity, Strong Pareto, and Weak Preference Continuity, and a liberal principle of Non-Interference that generalises IBP.