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Arrow's Impossibility Theorem

 

            In his essay, "The Arrow Impossibility Theorem," Eric Maskin discusses an assertion put forth by his former teacher, Kenneth Arrow. Arrow's theorem centers on his statement that, ".there is no good election method." Well, I will make the case that this is too strong a conclusion to draw; it's overly negative" (1). Two popular voting methods used in the United States are then described by Maskin, the plurality rule and majority rule. Maskin describes plurality rule as a voting method in, "which the winner is the candidate who is more voters' favorite candidate (i.e., the candidate more voters rank first) than any other. Thus, if there are three candidates X, Y and Z, and 40% of the electorate like X best (i.e., 40% rank him first), 35% like Y best, and 25% like Z best, then X wins because 40% is bigger than 35% and 25% - even though it is short of an over-all majority (2). He then gives his explanation of majority rule, which is, "the candidate who is preferred by a majority to each other candidate. For instance, suppose there are again three candidates, X, Y, and Z. 40% of voters rank X first, then Y, and then Z ; 35% rank Y first, then Z, and then X ; and 25% rank Z first, then Y, and then X. Based on these rankings, the majority winner is candidate Y, because a majority of voters (35% + 25% = 60%) prefer Y to X, and a majority (40% + 35% = 75%) prefer Y to Z" (2). After explaining these two voting methods, Maskin poses the question, "which voting rule is better to use" (3)? .
             Maskin proceeds to explain Arrow's Impossibility Theorem and how it attempts to answer the previously stated question. Arrow proposed a set of axioms and he intended that the best voting rule would be the one that fulfills every axiom. The axioms included that the election be decisive, there must be consensus, a requirement of non-dictatorship, and independence of irrelevant alternatives. Maskin then uses the 2000 Presidential election as an example to help illustrate the impossibility theorem, in particular, the election in Florida.


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