Preference domains and the monotonicity of condorcet extensions

摘要

An alternative is a Condorcet winner if it beats all other alternatives in a pairwise majority vote. A social choice correspondence is a Condorcet extension if it selects the Condorcet winners and nothing else - whenever a Condorcet winner exists. It is well known that Condorcet extensions are not monotonic (hence, not Nash implementable) when all preferences are admissible, but are implementable when restricted to a domain in which Condorcet winners always exist. We fill the gap by studying the intermediate domains and find that monotonicity is violated on all such domains. (C) 2015 Elsevier B.V. All rights reserved.