View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Research Papers in Economics DOCUMENTO CEDE 2005-63 ISSN 1657-7191 (Edición Electrónica) NOVIEMBRE DE 2005 CEDE ARROW’S IMPOSSIBILITY THEOREM IS NOT SO IMPOSSIBLE AND CONDORCET’S PARADOX IS NOT SO PARADOXICAL: THE ADEQUATE DEFINITION OF A SOCIAL CHOICE PROBLEM DANIEL CASTELLANOS* Abstract In this article, we do two things: first, we present an alternative and simplified proof of the known fact that cardinal individual utility functions are necessary, but not sufficient, and that interpersonal comparability is sufficient, but not necessary, for the construction of a social welfare function. This means that Arrow’s impossibility theorem is simply a consequence of forcing the individual utility functions to be ordinal. And second, based on this proof, this article establishes two necessary conditions for the adequate definition of a social choice problem. It is shown that, if these two conditions are satisfied, a number of desirable properties for a social choice are satisfied, including transitivity. This means that Condorcet’s paradox is simply the result of a social choice problem that is not well defined. Key words: Condition of independence of irrevelant alternatives, social choice, social welfare function, cardinality and interpersonal comparability, Arrow’s impossibility theorem, Condorcet’s paradox. JEL classification: I30, D60, D61. * BBVA Colombia and Universidad de los Andes. E-mail:
[email protected]. I deeply thank Enrique Pinzón and Carmen Helena Botero for helping me translate this article into English. I thank Dr. Gustavo Pineda for providing, through the surgery he performed in my knee and its sequels, that almost take my life, the adequate conditions for thinking about the issues here considered.